Tuesday, October 09, 2007

COMMON POSITIONING PROBLEMS: The Solutions!

OBJECTIVES:

No matter which modality we are using, no matter whether we are practicing screening or diagnostic mammography, no matter what: We still have to position our patients so that all the breast tissue is demonstrated.

That is always a challenge and all the help that comes our way is useful. Here are some tips regarding positioning dilemmas with some handy remedies. I hope they are helpful.


THE CC PROJECTION: “IF”

  1. The nipple is not in profile

If the nipple is not in perfect profile:

  1. Elevate the IMF a little higher

  2. Lift and pull the breast straight onto the bucky

  3. Use both hands to handle the breast

  4. (Hint): The nipple points toward the missing tissue



  1. The medial Cleavage is not open and visualized

If the medial cleavage is not visualized properly:

  1. Position from the medial side

  2. Lift and drape opposite breast over the edge of the bucky

  3. Do not press the patient’s face against the face protector

  4. Place her head beside and beyond the tube



  1. The lateral aspect or ‘Tail-of-Spence’ is not demonstrated

If the lateral aspect of the breast is not seen:

  1. The Patient’s arm should be relaxed by side

  2. Her palm should be supinated with her shoulder externally rotated

  3. Control your patient’s posture with your hand around her back on her contra-lateral shoulder

  4. She should be relaxed forward bent slightly at the waist

Release the breast to the compression with forward and medial orientation of your hand



  1. The pectoral shadow is not visible at the chest wall and/or the PNL is not within 1cm of the PNL on the MLO

If the ½ moon of pectoral shadow is not seen at the chest wall of the CC view and/or the PNL is of an inadequate length:

  1. Elevate the IMF until the tissue no longer moves easily along the chest wall
  2. Identify the edge of the pectoral muscle visible just under the clavicle
  3. Loosen the skin over the clavicle so the tissue moves easily
  4. Compress parallel to the pectoral edge just under the clavicle
  5. Release hand in a forward medial motion



THE MLO PROJECTION: “IF”

  1. The pectoral muscle is not demonstrated to or below the level of the nipple

If the pectoral muscle is not seen to the level of the nipple or below:

  1. Adjust your tube angle parallel to the obliquity of the patient’s pectoral muscle

  2. Move the breast medially and anteriorly from the lateral border until the pectoral pouches out next to the sternum

  3. Compress the projection parallel to the pectoral axis along the sternal edge



  1. The pectoral muscle is not relaxed and convex in shape

If the pectoral shadow does not appear convexly shaped:

  1. DO NOT rest your patient’s arm along the top edge of the bucky
  2. Patient’s shoulder should be open, relaxed
  3. The corner of the bucky high up and well back in the axilla
  4. Patient’s arm should be slightly bent hanging loosely down the back of the bucky
  5. Relaxed hand…NO gripping the handle



  1. The breast is not ‘up & out’ and/or the retro mammary space is not visualized behind the parenchyma

If the retro mammary space is obscured by parenchyma and the breast is not adequately ‘up & out’:

  1. Move the breast from the lateral edge medially

  2. Ensure the breast mound moves freely in your grip

  3. Support the breast tissue from the inferior border using you entire hand

  4. Immobilize the breast tissue on the bucky in the ‘up & out’ position using the edge of your hand to support the pectoral axis along the sternum

  5. Release the breast to compression with a distinct out and away motion



  1. The Infra-mammary Fold is not clearly seen curving to the abdomen un-obscured by wrinkles, folds or belly


If the IMF is not open and fold free:

  1. Support the breast and always release with and up & out motion

  2. Have the patient tilt her hips slightly backwards

  3. Do not release your hold on the breast until the projection is immobilized by the compression

  4. Gently run your thumb and finger down behind the breast along the IMF/belly border to clear folds, wrinkles and tummy


  1. Nipple is not in profile

If the nipple shadow is not in perfect profile:

  1. Make sure the patient’s feet are directly facing the bucky

  2. Control the breast from the mobile lateral border only

  3. Immobilize the breast parenchyma parallel to the pectoral muscle until the compression holds the projection

  4. (Hint): The nipple points toward the missing tissue

SUMMARY

Mammography is a sensitive, complicated and difficult specialty. All our patients vary as to body habitus, temperament and compliance. It is essential we demonstrate all the tissue, see it clearly and know that all the borders of the breast are verified.

Breast Imaging is an area of DI where we work autonomously much of the time. We are responsible for checking and correcting our own work. I hope these tips will assist in the arduous task of perfecting your technique and knowledge.

Friday, September 14, 2007

Are We Sensitive To Our Diverse Ethnic Environment?

OBJECTIVES:

Women from minority groups have been traditionally under served in mammography. The most common barriers facing this community are insufficient education concerning personal health care and little or no access to familiar, locally based heath care providers.

We are beginning to surmount some of these obstacles by providing government funded, neighborhood based, free breast screening and establishing community outreach programs to minority neighborhoods. But even when minority patients are able to gain access to conveniently located, low-cost mammography, language and/or cultural barriers make it difficult for them to receive full benefit from the procedure. It is of great urgency that the experiences and values of minority women be better understood so we can provide them with full use of prevention and early detection services.

BEFORE THE SCREENING

Our medical care system is modeled on middle class values and middle class education levels. Many low-income minority patients are completely unfamiliar with mammography. Our patient needs careful explanation and education about screening from someone who understands her language AND her socio-cultural background.

Minority women tend to wait for a crisis before seeking health care. The concept of preventive action is foreign to them. One way of emphasizing the need for early detection and prevention in these communities is to stress the importance of their lives on the lives of their children and grandchildren. Point out that keeping their health by early detection and intervention will keep them with their families longer. It will help keep them productive and active in the community for many happy years.

Many minority women have no idea that they are at risk from breast cancer. The perception is that breast cancer is a ‘white woman’s’ disease. They do not recognize themselves in the health promotions. The concept of increased risk to women of color must be reinforced before the screening begins so that our patient will relate to what is happening to her.

In many minority communities there are important taboos concerning anyone other than a spouse touching a woman’s breast. This patient must be carefully informed before the procedure that the mammographer will be touching and maneuvering her breasts. She must know that she will have to disrobe. It is important to tell her why all this is to take place. Always politely ask permission before any touching or positioning of the breast begins.

Fear of pain during mammography is widespread among minority women. They have extraordinary concerns about this. Even though, statistically, minority patients related less pain during mammography than their Caucasian counterparts. Therefore, even if the fear seems unfounded, it is important to take extra time and precautions when explaining the amount of pressure and the importance of breast compression to women from minority communities.

DURING THE SCREENING

Self-introduction and discourse with minority women must be handled discretely. When calling a minority patient her given name should never be used without the patient’s permission. Introduce yourself formally, using your first name, last name and title. Always use a formal greeting such as ‘Miss’, “Mrs.” or ‘Ms.’ and never resort to slang expressions such as ‘sweetie’, ‘dearie' or ‘sweetheart’. Many ethnic groups interpret this behavior as a racial or cultural slur. When greeting your patient always start with some polite introductory inquiry into the weather, the health of her family or children. Make any request to disrobe quiet polite and discrete. A gentle “Would you mind removing your blouse and bra for a few moments?” is considered respectful.

It is a common belief among minority groups that the use of any x-ray equipment will cause cancer. It is also widely held that pressing or excessive manipulation of the breast will cause ill health of various sorts including cancer. She must be assured that the mammogram will not cause any breast problems and that the mammographer will make every effort to be quick, efficient and sensitive.

The technologist must be prepared to see and accept cultural practices different from her own. Tips of acupuncture needles, circular suction cup marks from ‘steam cups”, freely injected silicon, tattooing, ritual scarring or tiger balm plasters are all common practice within certain communities. React to these customs with respect and treat your patient with dignity.

Women of various ethnic backgrounds may be hypersensitive about the size or shape of their breast tissue. It doesn’t matter whether your patient thinks she is too big or too small. It doesn’t matter whether she feels she is too tall, too short, too fat, too thin, too simple or too sick. We must treat EVERY patient as if she is the easiest client we have ever had. Take all the responsibility for doing the test. Never suggest that the patient is making it difficult. Just keep up a continuous stream of confidence boosting conversation. Speak softly, pleasantly and congenially; your attitude will travel through your voice.

Among the refugee community we may find a serious barrier to breast examination that we thank heavens, do not have to deal with often. Many women from refugee backgrounds have suffered rape, humiliation, abuse and torture. These women have braved great anxiety just to get to your facility they deserve all the respect and quiet dignity we can muster. Treat these patients gently; do not rush them through. Try to give them as much time and explanation as they need to get used to the idea of the test. Don’t push them beyond their tolerance. Have a list of counselors and help groups available but do not force information on them. Allow them to back out of the examination and try again later if necessary. Be alert to all the body language, don’t force eye contact, be receptive and always use appropriate family and friends for support if available.

Finally, many ethnic societies have a pathological fear of the word ‘CANCER’. In some cases the word itself is so disruptive that it inhibits the entire mammogram. Rather than compromise the whole breast imaging session, I suggest using ‘breast health’, ‘preventative testing’ or ‘early detection of problems’. In most situations, open and honest dialogue about cancer, its detection and prevention is the best way. However, if the mere word is going to drive your patient out of the department in panic, use a milder alternative.

AFTER THE SCREENING

Because so many minority women have such a limited knowledge of mammography, there may be a distorted perception of what happens after a screening mammogram. These women may think that the mammographer will come and tell immediately if she has cancer or not. If nothing is said she may misinterpret that to mean the test was negative, or worse, positive and run in frenzy to her physician. It is important to have a chat with this type of patient before she leaves the department and make sure she is comfortable with what happened to her and what will happen next.

Ideally, after the mammogram, there should be a meeting with the mammographer, the interpreter, the patient and her family to explain the facility’s physician reporting system and follow-up procedures. She should understand when and how her next appointment should be made and whom she can contact for information or further explanation.

CONCLUSION:

Every woman deserves individual attention, an appreciation of past experience, respect for her distinct belief systems and clearly conveyed instructions and explanations. Women from culturally diverse communities present us with a challenge in this area. With a little time, sensitivity and armed with the knowledge we need to deal with these patients we can make their medical experience valuable and pleasant.

Tuesday, August 14, 2007

Digital Tomosynthesis of the Breast

OBJECTIVES:

"Will tomosynthesis replace conventional mammography?" This is a provocative question and one that we must be consider. Dr. Daniel Kopans, director of breast imaging at Massachusetts General Hospital described positive experiences with tomosynthesis in 400 volunteers at MGH.

As new technologies emerge and are tested the breast imager must learn change and adapt or be left behind.

What is Tomosynthesis?

Digital tomosynthesis creates a 3-dimensional picture of the breast using X-rays. Currently, digital tomosynthesis is available only for research purposes. Digital tomosynthesis of the breast is different from a standard mammogram in the same way a CT of the chest is different from a standard chest x-ray. One is 3-dimensional; the other is flat. Tomosynthesis is a 3D digital technique that removes the effect of superimposed tissue. The principle is to reduce noise of overlapping normal breast tissue, improving detection of breast cancer.

"Looking at a 2D mammogram is like trying to look through a book with clear pages-you can see the letters but it is very hard to read them. It is much better if you can read each page individually," Kopans said.

Digital tomosynthesis takes multiple X-ray pictures of each breast from many angles. The breast is positioned the same way it is in a conventional mammogram, but only a little pressure is applied—just enough to keep the breast in a stable position during the procedure. The X-ray tube moves in an arc around the breast while 11 images are taken during a seven-second examination. Then the information is sent to a computer, where it is assembled to produce clear, highly focused 3-dimensional images throughout the breast. Early results with digital tomosynthesis are promising. Researchers believe that this new breast imaging technique will make breast cancers easier to see in dense breast tissue.

Made possible by a grant from the United States Army and the engineering expertise of the General Electric Company, a Tomosynthesis scanner was built and installed at MGH.


A

B

A) Tomosynthesis slice with patent lesion

B) Standard 2D LMLO view with obscure lesion


Standard 2D CC view with obscure lesion

Tomosynthesis slice with patent lesion

Preliminary Studies:

Breast cancer death rates that were constant for 50 years suddenly started to decline in the early 1990s, as the benefits of mass screening became evident. Such benefits are now well accepted, but there is still room for improvement. Out of 100 women with breast cancer today, 80 cases will be detected. Of the cancers that are identified, 68 (85%) will be seen with mammography, while 12 will be detected in clinical breast exams. Yet 20 will go unobserved. Mammography screening is good for detecting cancers that grow moderately quickly, but can miss very fast-growing cancers. Mammography is excellent and beneficial, but we need to continue to research better, faster and more accurate methods of breast cancer detection.

LESION VISIBILITY

In a pilot study of 40 women at MGH (a subgroup of the 400 volunteers), breast tomosynthesis helped improve lesion visibility compared with conventional mammography. With breast tomosynthesis, radiologists were able to see masses and architectural distortion better than with conventional mammography. In the pilot study, six out of seven malignant lesions identified on ultrasound that were occult on mammography were identified by tomosynthesis. At the special focus session, Rafferty presented an image of a young woman with very dense breast tissue and a palpable mass. A malignancy was not visible on the mammogram but was evident on ultrasound as well as on a breast tomosynthesis image. A second malignancy in the same breast was occult on mammography and ultrasound but was demonstrated by tomosynthesis. The reduction of noise from overlapping tissue (using tomosynthesis) also proved to be beneficial in imaging women with fatty tissue.

REDUCING RECALLS

Up to one-quarter of women recalled for follow-up after a mammogram ultimately turn out to have no abnormality. Researchers at Dartmouth Hitchcock Medical Center found that tomosynthesis could dramatically reduce the rate of false-positive mammograms. In a study of 98 patients with abnormal mammograms in 99 breasts, tomosynthesis as a screening follow-up tool was equivalent or superior to diagnostic mammography in nearly 87% of cases. There were 112 screening abnormalities in the study group. If tomosynthesis had been used as an adjunct to mammographic screening, the recall rate could have been cut by 40. On the basis of this very small study, tomosynthesis is equivalent or superior to mammography for diagnosis. It will offer recall reduction and better reflects the reality of the breast, translating into a more accurate diagnosis. Because of the very small scope of this study it is only indicative and must be backed up by larger clinical trials.

It took 20 seconds to acquire a tomosynthesis image and one minute to reconstruct the image. Two views were taken in most cases. Tomosynthesis proved superior to diagnostic mammography in 37 cases, equivalent in 49 cases, and inferior in 13 cases. Tomosynthesis was deemed inferior in some cases which involved calcifications; in addition, quality may have been affected by the lengthy acquisition time and motion artifact. Of the total number of potential abnormalities, five were cancers. Three cancers were detected by both mammography and tomosynthesis, and two cases were occult for both techniques.

The Challenge: This digital technique enabling physicians to “page through” the interior of the breast without obstruction by surrounding superimposed tissue has been hampered in the past because the method was computationally intense and took far too long for use in a clinical setting. Many of the tomosynthesis clinical trials to date have been disadvantaged by these challenges.

Is there a Possible Solution? Designers at Mercury Computer Systems implemented an iterative reconstruction algorithm called Maximum Likelihood Expectation Maximization which initially produced very high quality images. Engineers mapped the algorithm to a specialty graphics processor with a unique programmable rendering pipeline. Careful construction of the software port was required to overcome memory, bandwidth and instruction set limitations while optimizing run-time performance. The latter was reduced from five hours to five minutes. In pre-clinical testing, digital breast tomosynthesis permitted physicians to find cancers earlier and more easily, and to differentiate benign versus malignant lesions while simultaneously reducing false positives.

New and Better Tools:

  • Digital Breast Tomosynthesis imaging system, co-developed by Massachusetts General Hospital and Mercury Computer Systems

  • GE Healthcare (Waukesha, WI) Senographe 2000 Digital Mammography System

  • NVIDIA (Santa Clara, CA) Quadro graphics processor Maximum Likelihood Expectation Maximization algorithm, co-developed by Brandeis University

Is the Solution Effective? The ensemble of observed results, software implementation and acceleration hardware has confirmed that digital breast tomosynthesis improved cancer screening accuracy, lowered costs, increased patient comfort and reduced exposure to ionizing radiation. Deaths from breast cancer dropped twenty percent over past decade, largely due to widespread screening mammography. Digital breast tomosynthesis’ superior ability to display lesions which otherwise might be masked could reinforce early detection and further reduce death rates. The Massachusetts General Hospital-Mercury Computer Systems technique sped up image reconstruction by a factor of sixty.

CONCLUSION:

Before digital breast tomosynthesis can be sanctioned for general use, it must be shown to be more effective in saving lives than conventional mammography. In light of the preliminary studies done in clinical settings such as MGH where digital breast tomosynthesis pinpointed seven cases which were not seen with mammography. Along with much engineering research making the new modality faster, clearer and easier to use; clearly, the stage is set to validate the technology and to propel digital breast tomosynthesis from a research tool into wide-spread clinical practice. Embracing change enhances knowledge and knowledge is power. Claim your power!

Sunday, March 04, 2007

QC for DIGITAL MAMMOGRAPHY: As Discussed in the DMIST Trial

OBJECTIVES:

For a QC program to be practical and able to be followed by all facilities, some pragmatic decisions about the usefulness of individual tests and scope and extent of site survey testing must be made. It was found in the DMIST trial, that the testing process was quite time consuming and that, while some of the information was relevant to the initial characterization of digital systems, it was of limited use for QC purposes. In addition, if one test was the same as a number of other, that test should be used first, and only if the system fails the initial test should it be necessary for the physicist or service person to perform further, more selective diagnostic tests. In this work, the tests used in DMIST are considered in three categories: A) THE PERFORMANCE OF THE IMAGE ACQUISITION SYSTEM, B) the dose and image quality, and C) the image display system. The objective of each test was reviewed briefly and the pass/fail criteria are presented. Based on experience from DMIST, the utility of the test is discussed and modifications to the method of carrying out the test, including its elimination from the program and/or changes to the pass/fail criteria, are recommended. The intent is to develop a harmonized set of tests, and also allow for cross-vendor validation of system compatibility.
  1. THE IMAGE ACQUISITION SYSTEM
Unit evaluation, breast thickness accuracy, maximum compression force, viewing conditions:

Objective: To ensure that all locks, detents, angulation indicators, and mechanical support devices for the x-ray tube and breast support assembly are operating properly and that the DICOM header information is correct. The overall safety of the equipment is verified, and problems that might interfere with general operation are detected. A nonexclusive list of items to be checked regularly by the technologist covers most areas of outwardly observable physical faults. The physicist does a more thorough evaluation.

Pass/fail criteria: A number of the items on the list are subjective with suggested performance targets. Evaluation requires diligence and discernment on the part of the technologist. Where tests have objective measures, pass/fail criteria are similar to those for SFM systems through MQSA.

DMIST results: There were very few significant problems found at physics inspections, but it should be noted that these facilities were highly motivated, and had regular reinforcement of QC policies. The most common failure identified by physicists was the absence of posted technique charts. This was justified in most cases because the computer displayed a recommended technique, and there were no manual techniques used at those facilities. The most common problems seen by the technologists were those related to viewing conditions and monitors.

Effectiveness: Regular checks by the technologist ensure that monitors are appropriately cleaned and that viewing conditions are appropriate. Some mechanical problems were found and service visits were scheduled to prevent downtime.

Recommendation: DMIST recommended that this test set be retained, and that it be performed weekly by the technologist. The physicist should perform a thorough inspection on each annual visit. Additional items which must be documented include: checking DICOM image header compliance for proper labeling, date, time, and time zone, all of which might get changed when software is upgraded. It is especially important that indicated breast thickness is accurate, as this affects technique selection and resultant breast dose.

CR Imaging plate fogging:

Objective: To confirm that computed radiography CR plates are not fogged by radiation in their storage location.

Pass/fail criteria: There should be no evidence of fogging on the image. The shadow of a coin taped to the front of a cassette and left in place through a full day of imaging should not be visible even at the narrowest display window setting.

DMIST results: No evidence of imaging plate fogging was seen.

Effectiveness: There is a low probability of failure.

Recommendation: This test is not recommended to be performed for routine QC.

Collimation and alignment:
Proper collimation of the x-ray field is necessary to ensure there are no unexposed portions of the image receptor and that patients are not needlessly exposed to stray radiation. Proper alignment of the edge of the compression paddle with the chest-wall edge of the image-receptor holder assembly is necessary for proper positioning and compression of the breast. Note that for CR, the image receptor is used with a number of different x-ray units and it is the alignment of the unit that is being evaluated in the following tests.
  1. X-ray field, field indicator and image field congruency.

  2. Objective:
    To evaluate whether the field as indicated by the machine, positioning light or other indicator matches the true x-ray field and whether the x-ray field is congruent to the image receptor.

    Pass/fail criteria: The sum of the x-ray field-indicator misalignments in the left-right and anterior-posterior directions should not exceed 2% of the source-to-image receptor distance (SID). The x-ray field should cover the entire displayed area, and no edge of the x-ray field should extend beyond the image receptor by more than 2% of the SID. Additionally, the x-ray field must not extend beyond the shielded area provided by the breast support except at the chest wall side.

    DMIST results: There were some inconsistent results in the different units. The high failure rates for the Fischer system arise from discrepancies between the points when x-ray exposure begins and ends during the scan, adjustable by the service engineer and the field markings printed on the tabletop at the factory. There is no radiation hazard associated with this failure, provided that the x-ray detector or surrounding shielding absorbs the full area of the primary x-ray beam.

    Effectiveness: Accurate indication of the active image area is necessary for correct patient positioning. From experience with film/screen systems, this test is useful for detecting gross errors in collimation adjustment or damage to the collimator device.
    Recommendation: We recommend that the collimation tests be performed annually, and whenever major components that could affect alignment of collimation, x-ray tube, collimator parts, detector assembly and/or scanning drive are repaired or replaced. In the future, this test will need to be done with a fluorescent screen, self-developing film, or an electronic “edge of field” imager because most facilities will not have access to a film processor.

  3. Compression paddle and image receptor—Excluded tissue at chest wall.

  4. Objectives: To ensure that the compression paddle is in the appropriate position and to determine the amount of tissue that is not imaged by the mammographic unit when a patient is positioned as closely to the unit as possible. A phantom was imaged to assess the amount of tissue excluded from the image at the patient’s chest wall.
    Pass/fail criteria: The edge of the paddle is not to be visible in the image. Not more than 7 mm should be excluded.

    Effectiveness: On some units, the paddle extension is adjustable, and improper alignment could result in poor positioning of the breast. If the edge of the compression paddle extends too far beyond the image receptor edge, the patient’s chest is pushed away from the image receptor and some breast tissue will be excluded from the image. If the edge of the compression paddle does not extend far enough, the breast tissue will not be properly pulled away from the chest wall, resulting in poor compression at the chest wall, and the vertical edge of the compression paddle could obscure clinical information. Mechanical support structures or clearance for the chest-wall edge of the detector may result in un-imaged tissue.

    Recommendation: It is recommended that the collimation test be performed annually and following service to the x-ray tube or collimator or whenever the alignment of the breast support to the detector is adjusted. The 7 mm limit for missing tissue was found to be satisfactory in that all systems could be adjusted to achieve compliance.
KV Accuracy and reproducibility:

Objective: This test evaluates the kilovoltage provided by the generator.

Pass/fail criteria: The measured kV must be within 5% of the nominal kV and the coefficient of variation between four successive exposures at the same kV setting must be less than 0.05.
DMIST results: Only one measurement exceeded the 5% limit.

Effectiveness: Given the stability of modern x-ray generators, kV accuracy and reproducibility need not be tested as part of routine QC. Furthermore, noninvasive test instruments estimate kilovoltage based on beam quality and are less precise than voltage meters that are connected directly to the generator circuitry. Measurements of the half-value layer (HVL) of the x-ray beam will detect any gross problems with kV output, but for this to be effective as an alternative to measurement of kV, it is necessary to have more stringent criteria for the value of HVL and its consistency over time.

Recommendation: It is recommended that a measurement of HVL be used as an assessment of beam quality. KV should not be measured as a routine practice, but only by a service engineer using appropriately calibrated equipment at installation and when the generator is serviced.

Tube output, linearity, output rate, and reproducibility:

Objective: This test ensures that tube x-ray output rate, linearity, and reproducibility meet MQSA requirements over a range of clinically relevant settings of kV, x-ray target, and beam filter.

Pass/fail criteria: For generator linearity, the output (mR/mAs)measured across a range of mAs settings was required in DMIST to remain within 10% of the mean tube output and increase monotonically with increased kV settings. The exposure output rate at 28 kV for those systems with Mo/Mo target filter combinations was required to be at least 800 mR, 7 mGy air kerma, as specified by MQSA for film/screen systems. Output reproducibility requires the COV for four successive exposures to be less than 0.05.

DMIST results: There were five failures of tube output linearity in 143 testing instances. Two of the four failures were attributable to measuring the output at low mAs settings, well below the manufacturer’s current recommended range of operation. One of the errors is consistent with an operator data transcription error. None of the measurements of tube output, output rate, and output reproducibility indicated a failure.

Effectiveness: Modern x-ray generators used in FFDM systems are universally of high-frequency design and incorporate internal feedback and correction circuitry that maintain virtually constant kV and mA during exposures. Exposure time is also controlled electronically and is highly reliable. X-ray tube output was found not to vary over long time periods.

Recommendation: DMIST believes that it is still worthwhile to include the measurement of x-ray tube output under different tube target/filter/kV combinations as part of a routine QC program as an overall performance check, and also because these data are necessary for computing estimated mean glandular dose. However, all current mammographic x-ray sources easily meet the requirement for output rate, and performance of that test is not recommended. Testing mR/mAs and HVL will provide a warning of generator and spectral problems and will prompt diagnostic testing. It is not recommended to directly evaluate output linearity and exposure linearity. Image noise tests will provide a surrogate test for problems related to linearity and/or reproducibility.

Detector linearity and reproducibility:

Objective: To evaluate the linearity of the detector response, the ratio of mean pixel value (MPV) to measured entrance exposure is tested for constancy.
Pass/fail criteria: The acceptance criterion for detector linearity is that at any point over a range of mAs, with other technical parameters constant, this value does not vary from its mean by more than 10%. For CR plates, sensitivity is deemed to pass if the S-number is within 15% of the target value. The limit on the COV for detector reproducibility measurements is 0.05.
Effectiveness: Tests of linearity and reproducibility are helpful for characterizing detector response, but once the mammography unit is installed are of marginal utility.

Recommendation: DMIST suggests that it should not be necessary to measure short-term detector reproducibility and linearity as part of routine QC. Instead, detector linearity and reproducibility should be measured only as a diagnostic tool, when irregularities are observed: shift of measured MPV or “S-numbers” on signal measurements obtained from the technologist’s weekly uniform phantom image.

Logging of this information could be automated and unacceptable deviations could be used to trigger a warning message, prompting investigation of whether the deviation arose from the x-ray generation system or from the detector.

Half-value layer:

Objective: This test evaluates the effective energy of the x-ray beam. The HVL of the x-ray beam should be high enough to avoid excessive dose to the breast, while not so high that subject contrast is reduced to an unacceptable degree. The test also ensures that the x-ray beam quality is consistent with the target, filter, and kV selected, and enables the calculation of mean glandular dose.

Pass/fail criteria: At a given kV setting in the mammographic kilovoltage range (below 50 kVp), the measured HVL with the compression paddle in place must be within the range set out in the ACR Quality Control Manual.7 For the upper limit, additional values of the constant, (c) have been defined. For W/Mo target/filter combination, c=0.28 and for W/ Al, c=0.32.
DMIST results: Of 396 measurements of HVL, no failures were recorded. The half-value layer showed little variation for any of the units.

Effectiveness: If the HVL for film/screen units is excessive, subject contrast will be reduced. For FFDM, with the capability of contrast manipulation, minor changes in HVL will have much less impact on image contrast than with SFM systems. Nevertheless, if kV is not measured routinely, HVL provides a check for variations in beam quality. In addition, knowledge of the HVL is required to estimate mean glandular dose.

Recommendation: This test should be performed annually. The HVL should be evaluated for each filter and for at least one kV that is typical of clinical operating techniques. DMIST recommend that HVL tables should be provided by the manufacturer for each FFDM model to facilitate dose calculations and to allow verification of correct HVL. These tables should specify the expected HVL under typical target/filter/kV combinations for clinical use. After initial testing, if the HVL is compliant with the manufacturer’s specification, the measured value should be adopted as the reference value and changes from that value tracked. The currently permitted range of HVL is very wide, and designed to accommodate a range of equipment designs; sensitivity to changes in HVL will be easier to detect if there is an established operating point. In the DMIST measurements, it was found that HVL varied typically by no more than 3%. A requirement that HVL be constant within 6% seems to be reasonable.

Focal spot:

Objective: This test ensures that the spatial distribution of x-ray emission from the focal spot in contact or magnification mode does not unduly degrade spatial resolution of the image.
Pass/fail criteria: The limiting effective spatial resolution in line pairs/mm for a bar pattern, placed 4.5 cm above the breast support table, was measured on a mammographic SFM receptor placed on the breast support surface. The MQSA film/screen criteria were employed; the minimum required limiting resolution was; 11line pairs/mm with the pattern bars perpendicular to the anode-cathode axis and 13line pairs/mm with the pattern bars parallel to the anode-cathode axis. Where magnification capability was available, systems were tested according to the same criteria using the small focal spot with the resolution pattern placed 4.5 cm above the magnification stand.

DMIST results: All but 5 of 246 measurements met the MQSA requirements. Of those that failed, three were taken using the magnification stand, and were just outside the limits. There was no measurable reduction of overall spatial resolution on mammographic units which failed this test.

Effectiveness: For contact mammography, the effective resolution provided by the focal spot is considerably higher than the resolution limit imposed by the digital detector and therefore has little influence on the overall MTF of the system. A test of system MTF is considered to be a more sensitive, objective, and relevant measurement of resolution, and is capable of detecting problems with the focal spot, synchronization errors, and other factors affecting system resolution. As more facilities switch to digital imaging, the film and processors needed to make this test will become unavailable.

Recommendation: The separate measurement of focal spot resolution using film/screen images need not be performed, except as a diagnostic test to evaluate resolution problems detected using the MTF test.

Saturday, February 03, 2007

Digital Mammographic Image Screening Trial: What do the studies indicate?

OBJECTIVES:
There have been several very relevant studies, clinical trails and research projects carried out with regard to full field digital mammography. The results of these endeavors have had significant impact on our professional lives.

These studies showed that digital mammography was significantly better that film mammography in screening women who were under age 50, or women of any age who had very dense breasts, digital mammography allows improvement in image storage and transmission because images can be stored and sent electronically. Secondary goals of some of these projects have been to measure the relative cost-effectiveness of both digital and film technologies, and the effect on participant quality of life due to the expected reduction of false positives.

Death rates from breast cancer have been declining since 1990, and these decreases are believed to be the result, in part, or earlier detection and improved treatment. One of these improvements is certainly digital imaging.

How is digital mammography different from film mammography? Both digital and film mammography use X-rays to produce an image of the breast.
In
film mammography, which has been used for over 35 years, the image is created directly on a film. While standard film mammography is very good, it is less sensitive for women who have dense breasts. Prior studies have suggested that approximately 10 percent to 20 percent of breast cancers that were detected by breast self-examination or physical examination are not visible on film mammography. A major limitation of film mammography is the film itself. Once a film mammogram is obtained, it cannot be significantly altered; if the film is underexposed, for example, contrast is lost and cannot be regained. Digital mammography takes an electronic image of the breast and stores it directly in a computer. Digital mammography uses less radiation than film mammography if used correctly by qualified mammography technologists. Digital mammography allows improvement in image storage and transmission because images can be stored and sent electronically. Radiologists also can use software to help interpret digital mammograms. One of the obstacles to greater use of digital mammography is its cost, with digital systems currently costing approximately 1.5 to 4 times more than film systems.

How was Digital Mammographic Image Screening Trial conducted?
The Digital Mammographic Imaging Screening Trial (DMIST) is the most important digital trial to date. It was begun in October 2001and enrolled 49,528 women, who had no signs of breast cancer, at 33 sites in the United States.

On the appointment day, women provided background health information and filled out brief questionnaires. They also had both digital and film mammograms taken on that day, each with a minimum of two views of each breast. Two different certified radiologists interpreted the conventional and digital mammogram exams for each individual patient. All radiologists who participated read both types of mammograms, and each radiologist read approximately an equal number of mammograms of each type. Participants were asked to return in one year for their annual mammogram. At that time, a mammogram was performed as part of routine health care. Women, who were not able to return to the same site as in year one, were asked to submit films from another institution for review by study radiologists.

Why was DMIST important?

For women, breast cancer is the most common non-skin cancer and the second leading cause of cancer-related death in the United States. Death rates from breast cancer have been declining since 1990, and these decreases are believed to be the result, in part, of earlier detection and improved treatment. DMIST was performed to measure relatively small, but potentially clinically important, differences in diagnostic accuracy between digital and film mammography. While any differences that were detected might be relatively small, they could improve breast cancer detection for all or some groups of women.

Digital mammography is a newer technology that is becoming more common. Currently, approximately 8 percent of breast imaging units provide digital mammography. Past trials of digital mammography have shown no difference in diagnostic accuracy between digital and film mammography. The U.S. Food and Drug Administration (FDA) trials and three smaller screening trials showed no significant difference in the performance of digital mammography vs. film mammography. These studies were limited, however, because they each included only one type of digital detector and had relatively small numbers of patients, perhaps limiting their ability to detect small differences in diagnostic accuracy.

Who were the women who enrolled in DMIST?
Over 49,500 women who were requesting their usual breast cancer screening mammogram were recruited at 33 sites in the United States and Canada. The women had no breast cancer symptoms, and they agreed to undergo a follow-up mammogram at the same participating site or provide their mammograms from another institution for review one year from study entry. All women reviewed and signed the study consent form.

The following women were ineligible:
  • pregnant women
  • women with breast implants
  • women who had undergone a screening mammogram in the past 11 months
  • women with a focal dominant lump, which is defined as a single lump felt by a woman or her doctor
  • women with a bloody or clear nipple discharge
  • women with a history of breast cancer treated with lumpectomy
Breast cancer status for DMIST participants was determined through available breast biopsy information within 15 months of study entry or through follow-up mammography ten months or later after study entry.

Who organized the study and how much did it cost?

The American College of Radiology Imaging Network (ACRIN) coordinated the study. ACRIN is a Cooperative Group sponsored by the Division of Cancer Treatment and Diagnosis at the National Cancer Institute (NCI). Enrollment began in October 2001. On Nov. 14, 2003, DMIST reached its targeted 49,500 participant recruitment goal. ACRIN is a network of physicians, scientists, and medical institutions that have joined together to conduct clinical trials of new medical imaging technologies. The total cost of the digital mammography trial was about $26 million.

Which digital mammography equipment was included in DMIST?

General Electric Medical Systems, Fuji Medical Systems, Fischer Imaging, and Hologic digital mammography systems were tested in the trial. Of these, all except for the Fuji system are already FDA-approved and available for clinical use in the United States.

How important is reader training in interpreting digital mammography?

Breast cancer has a very similar appearance on digital and film mammograms, but the display of the images on monitors instead of film requires additional reader (radiologist) training. Under the federal law that governs mammography in the U.S. (the Mammography Quality Standards Act) radiologists who switch from interpreting film to interpreting digital mammography must undergo some additional training.

STUDY RESULTS
What were the main results of DMIST?
DMIST showed that, for the entire population of women studied, digital and film mammography had very similar screening accuracy. Digital mammography was significantly better in screening women who fit any of these three categories:
  • under age 50 (no matter what level of breast tissue density they had)
  • of any age with heterogeneously (very dense) or extremely dense breasts
  • pre- or peri-menopausal women of any age (defined as women who had a last menstrual period within 12 months of their mammograms)
There is no apparent benefit of digital over film mammography for women who fit ALL of the following three categories:
  • over age 50
  • those who do not have dense or heterogeneously (very dense) breast tissue
  • those who are not still menstruating
In addition, there was no statistically significant difference in the accuracy of digital mammography compared to film according to digital mammography machine type, race, or breast cancer risk. These results suggest that for women who fall into three subgroups (women under age 50, women with heterogeneously dense or extremely dense breasts, and pre- and peri-menopausal women), digital mammography may be better at detecting breast cancer than traditional film mammography. Approximately 65 percent of the women in DMIST fit into one of the three subsets that showed a benefit with digital mammography.

Some earlier studies had suggested that digital mammography would result in fewer false positives than film mammography, but the rates of false positives for digital mammography and traditional mammography were the same in DMIST.

How many of the study participants were diagnosed with cancer?

During the course of the study, including initial screening and follow-up, 335 women were diagnosed with cancer. In general, cancers detected by either film or digital mammography were similar in histology (microscopic structure) and stage (how advanced they were). However, lesions detected by digital mammography and missed by film in women under age 50, in women with heterogeneously dense or extremely dense breasts, and in pre- and peri-menopausal women, included many invasive cancers and medium and high grade in situ lesions. Many of these cancers were confined to the breast at diagnosis; that is, they had not yet spread to the lymph nodes under the arm. These are precisely the lesions that must be detected early to save more lives through screening. In situ lesions in the breast are those confined to the breast duct without invading the surrounding breast tissue and are known as DCIS, or ductal carcinoma in situ.

Neither digital nor film mammography found all the breast cancers in the study population. Women who develop lumps, breast changes, or symptoms after screening mammography should report them to their physician even if their mammogram showed no signs of breast cancer.

Was the screening mammography performed in DMIST, both digital and film, accurate?

Both digital and film mammography had sensitivities (the ability to tell if a cancer is present) for breast cancer of 70 percent in the overall study population using the conventional methods for measuring sensitivity in a breast cancer screening trial. The sensitivity for women with dense breasts was only 55 percent for film mammography while the sensitivity for digital mammography was 70 percent. The overall rate of 70 percent is within the expected rate of detection. Specificities, or the ability to tell correctly that a cancer is NOT present when the breasts are normal, were high for DMIST, just as would be expected of screening mammography. Using one year follow-up interval, specificities for both digital and film mammography were 92 percent for the overall population.

Do the trial results suggest that women's lives will be saved if they undergo digital mammograms and they are in one of the three groups that showed a benefit with digital mammography?

DMIST was not designed to study breast cancer mortality, as that would have been a much longer and more costly study. The improved diagnostic accuracy of digital mammography in the subgroups of women found in DMIST may not translate into saved lives. However, the types of lesions that were found by digital mammography and not by film in these subgroups of the women were the types of cancers that can lead to death -- that is, invasive cancers without evidence of metastasis to axillary lymph nodes (lymph nodes under the arm and next to the breast that is affected by cancer) at the time of diagnosis and medium and high-grade in situ lesions (DCIS).

Randomized clinical trials that have studied mortality have shown a reduction in mortality from breast cancer with the use of screening mammography, ranging from 18 percent to 30 percent depending on the age of the women. DMIST results indicate that screening with digital mammography will detect at least as many breast cancers as film mammography over the whole population, and more advanced or serious breast cancers in women in the three subsets of the population. This suggests that at least as many -- and possibly more -- lives will be saved with digital mammography as are now saved by screening with film mammography.

Do the trial results indicate that ALL women should get digital mammograms instead of film mammograms for breast cancer screening?

No. The study results indicate that only women who fit in ANY of these three categories would benefit from digital mammography instead of film mammography:
  • under age 50 (regardless of level of breast tissue density)
  • of any age, with heterogeneously (very dense) or extremely dense breast tissue
  • pre or peri-menopausal women of any age (defined as women who had a last menstrual period within 12 months of their mammograms).
According to the results, women who fit ALL of the following three categories would not benefit from digital mammography instead of film mammography:
  • over age 50
  • those who do not have dense or heterogeneously (very dense) breast tissue
  • those who are no longer menstruating.
At present, only 8 percent of the mammography units in the United States have digital systems, whereas approximately 40 percent of women undergoing screening mammography have dense breasts. It will be impossible for all women who have dense breasts to receive digital mammograms, at least for the near future. As more digital mammography systems become available, more women in the groups who are likely to benefit from digital mammography will have access to this technology.

What were the secondary goals of this trial and what were those results?

Secondary goals included:
  1. measurement of the relative cost-effectiveness of both digital and film technologies, as digital mammography costs 1.5 to 4 times more than film mammography
  2. the measurement of the effect on participant quality of life due to the expected reduction of false positives
The results of these parts of the study are still under analysis and will be presented at a later date. In fact, even though a reduction in false positives with digital mammography was expected, none was found in DMIST. The effect of false positive results on quality of life will be reported at a later date.

Reader (radiologist) studies also were conducted using the mammograms obtained in DMIST. What were the studies and what were the results?

Seven controlled reader studies were used to measure the following:
  • diagnostic accuracy of softcopy (displayed on a computer monitor) vs. printed film display for digital mammography
  • effect of disease prevalence (percent of trial participants who actually had breast cancer) on reader interpretation performance
  • effect of breast density on the diagnostic accuracy of digital mammography vs. film mammography
  • diagnostic accuracy of each of the four individual digital mammography units vs. film mammography
The analysis of the reader studies has not been completed at this time.

Are there other possible advantages of digital mammography over film mammography?

Digital mammography offers other advantages over film, including improved ease of image access, transmission, retrieval and storage, and lower average radiation dose without a compromise in diagnostic accuracy. In addition, digital mammograms are less likely than film mammograms to be lost.

What levels of radiation are used for digital mammography vs. film mammography?

In DMIST, digital mammograms required approximately three quarters the radiation dose of film mammography. However, the dose in film mammography is quite low and poses no significant danger to patients.

CONCLUSIONS:

Our professional life is never static. Mammography is a fluid, fast paced arena; changing and growing with every new technologic discovery. Digital Imaging is here and here to stay. The clinical trials are a tedious and laborious process. They take years to implement, study and complete. The tally is in on Digital mammography and the answer is a new and valuable tool in our fight against breast cancer. Learn and grow and serve our health care consumer better.