Computer-aided detection (CAD) is widely used and accepted as a
solution for marking potential abnormalities on mammography, breast MRI,
chest, prostate exams, and more. Over the years, clinical studies have
found evidence that CAD marks too many false positives, casting doubt on
the efficacy of the technology.
Nonetheless, many radiologists
say they won’t do reads without CAD; what gives the technology its
staying power may be less a matter of absolute science than a matter of
The CAD controversy
The proportion of
screening mammograms in the United States using CAD increased from 39%
in 2004 to 74% in 2008, according to Rao et al.1 Yet,
questions surrounding the efficacy of using CAD for breast imaging
prompted a recent study by Fenton et al, to investigate “whether CAD
improves breast cancer detection when used by community radiologists.”
researchers designed a nonrandomized, retrospective study to evaluate
an “association between CAD use during film-screen screening mammography
and specificity, sensitivity, positive predictive value, cancer
detection rates, and prognostic characteristics of breast cancers
(stage, size, and node involvement).”2
analyzed 1.6 million film-screen mammograms conducted at Breast Cancer
Surveillance Consortium facilities in 7 states from 1998 to 2006. The
results found that false-positive readings following CAD implementation
increased 0.5%, and the researchers concluded that “CAD use during
film-screen screening mammography in the United States is associated
with decreased specificity, but not with improvement in the detection
rate or prognostic characteristics of invasive breast cancer.”2
the clinical trial was very large, enrolling 684,956 women, many
mammography experts saw significant flaws in the study methodology,
analysis, and presentation of results. The study looked only at
film-screen mammograms, not digital mammograms, which have supplanted
film-screen as today’s standard of care.
“[The study] is not
completely relevant today because it is based on film-screening
mammography, and approximately 80% of the facilities currently in the
United States are digital,” indicated Stamatia Destounis, MD, Managing
Partner at Elizabeth Wende Breast Care (EWBC) in Rochester, NY.
presented in a negative way, the study results actually demonstrate the
effect CAD should have when used over a period of several years; upon
introduction, recall rates and cancer detection rates will both
increase, as previously unseen cancers are detected. After several
years, recall rates and detection rates return to baseline, with the
same percentage of cancers being detected,though at an earlier stage.
the study actually found that CAD showed a decided advantage in
detection of ductal carcinoma in situ (DCIS), one of the earliest
indicators of breast cancer.
How to use CAD
more than 30 peer-reviewed articles published in major scientific
journals have shown positive results from historically controlled
studies using CAD in a screening environment, the study by Fenton et al,
has caused quite a stir—putting into question a widely adopted tool.
Fenton study may be most beneficial by opening discussion on an
important question—how is CAD software designed for use in screening
From the perspective of many leading radiologists
specializing in mammography, CAD is designed to work like a second pair
of eyes, reviewing a patient’s mammogram after the radiologist has
already made an initial interpretation. “CAD is another look. It does
not interpret the mammogram for you,” said Dr. Destounis.
common sense that a second pair of eyes is going to help you pick up
something you might miss. CAD highlights findings that are potentially
important,” said Robin Shermis, MD, MPH, Medical Director of The Toledo
Hospital Breast Care Center, ProMedica HealthCare in Toledo, OH.
the controversy surrounding the efficacy of CAD for mammography,
radiologists continue to view CAD as an essential instrument in their
At EWBC, a renowned breast center that performs an
estimated 80,000 mammograms annually, CAD has been another useful tool
in their screening process since July of 2000. Radiologists there are
specialists in mammography, and they have 2 CAD solutions at their
disposal: R2 ImageChecker CAD by Hologic and iCAD for mammography.
is another tool we use every day in our clinical practice,” said Dr.
Destounis. “Overall, CAD is very good at marking calcifications. For
masses, and especially architectural distortion, lesions that may be
visible on one view, sometimes it marks it, sometimes it doesn’t. It may
not mark a mass on both views, so you have to jump on those based on
one view.” She added, “We rely on the mammogram as our gold standard and
utilize CAD as another tool.”
Breast MRI makes it work
purpose and function differ across applications. CAD for breast MRI,
for example, serves primarily as a workstation to read cases more
As a workflow tool, breast MRI CAD helps radiologists
manage the large sets of data, it calculates critical measurements,
corrects for motion artifacts, characterizes abnormalities on the
images, and conveys information to the referring physicians and
patients. These automated steps save the radiologists time, enhancing
their overall performance.
Toggling through the large MRI datasets
can result in lengthy reads. To better manage the data files, CAD for
breast MRI presents simultaneous axial, sagittal, and coronal views of
acquisitions or postprocessed image sets using multiplanar
reconstruction (MPR). Users can set up side-by-side comparisons of
pre-and postcontrast images. Color maps illustrate dynamic enhancement
curves for contrast washout,showing how contrast is taken up and
released by the breast tissue.
At The Toledo Hospital Breast Care
Center, where doctors conduct up to 7 breast MRI exams a day,
mammography interpreters rely on the Aurora CAD workstation.
allows you to quickly go through breast tissue and organize your
thoughts about findings to decide what may or may not be important.It
allows you to look at all 3 planes nearly simultaneously, to quickly,
efficiently, and accurately read a case to the point that we actually
read our cases in real-time,” said Dr. Shermis. “With the color-coded
CAD properties, we are able to interpret a scan quickly and go over the
results with the patient right there.”
If the doctors need a
second look with an ultrasound and then need to do a biopsy, Dr. Shermis
explained, they can perform an ultrasound and biopsy on the same day as
CAD provides 3-dimensional registration to compensate
for patient motion between data acquisitions. This contributes to more
accurate orthogonal and oblique views of lesions for MPR, maximum
intensity projections (MIP), and surface-rendering views.
MPR, you look at findings in the axial, coronal, and sagittal planes.
You can get a really good feel for the morphology of a lesion and where
it is located. It gives you subtracted views that isolate the areas of
contrast enhancement, and you can get these subtracted views in a planar
fashion or in 3-dimensions,” said Dr. Shermis.
feature, available on the ONCAD system from Invivo, analyzes MR images
to detect invasive and noninvasive suspicious lesions. It also
delineates the extent of disease by measuring margin sharpness, a
characteristic related to blooming, to help determine the degree of
CAD for lung: A new era
area of skepticism has surrounded screening for lung cancer. For years,
no clinical study had found a significant correlation between mortality
rates and screening for lung cancer with either x-ray or computed
tomography (CT). But that uncertainty may be clearing up, ushering in a
new era for lung screening and CAD.
In 2005, results from the
Prostate, Lung, Colorectal and Ovarian (PLCO) Cancer Screening Trial
found screening for lung cancer with chest x-rays can detect early lung
cancer but also can produce many false-positive test results, causing
needless extra tests.3
Nonetheless, it remains common practice to look for incidental findings and use CAD when reading chest x-rays.
take chest x-rays for patients preoperatively; some have pneumonia. But
no matter what they are done for, you always look for other findings to
make sure there are no abnormal lymph nodes and there are no lung
cancers that are not expected,” said Patricia Shapiro, MD,a Diagnostic
Radiologist at SouthCoast Medical Group, Savannah, GA, where doctors use
CAD for mammograms, breast MRI, prostate exams, and chest x-rays.
2010, SouthCoast Medical Group performed 3,100 chest x-rays using
OnGuard 5.1, a CAD solution designed to identify nodules that may be
early-stage lung cancer.
In Dr. Shapiro’s experience, the software
is capable of detecting nodules < 9 mm, although labeling indicates
it is designed to detect nodules between 9 and 30 mm. The false positive
(FP) rate for OnGuard is 1.3 FP per image.
“If CAD for x-ray lung
picks up a suspicious nodule,” Dr. Shapiro said, “I am much more likely
to bring the patient back for a CT scan. It adds confidence to a
decision that I may have made already.”
Dr. Shapiro admitted it is
harder to pick up lesions with chest x-rays, but on chest CT screenings
they have picked up Stage 1 lung cancerson a number of patients.
“Picking up Stage 1 lesions is ‘the Holy Grail,’” she said.
Holy Grail may be in reach according to new findings from the National
Lung Screening Trial (NLST), a multicenter, randomized,and controlled
trial. Conducted by the American College of Radiology Imaging Network
(ACRIN) and the National Cancer Institute’s Lung Screening Study Group,
the NLST enrolled 53,000 current and former heavy smokers aged 55 to 74
at 33 sites across the U.S. The study measured the effect of low-dose CT
screenings compared to chest x-ray on lung cancer mortality. It found a
relative reduction in mortality from lung cancer with low-dose CT
screening of 20.0% compared to x-ray on lung.4 The clinical trial demonstrated for the first time that the early detection of lung cancer can save lives.
there is no reimbursement in the U.S. for lung screenings, these
findings may sway some insurance companies to cover screening for lung
cancer using CT, and CAD as an add-on. A cost-effectiveness analysis
using the NLST data is under way and is designed to “guide decisions
about the best use of finite health care resources.”5
Some of the commercially available CAD for CT lung solutions include syngo LungCAD and syngo LungCARE CT by Siemens Healthcare as well as VCAR by GE Healthcare. syngo LungCAD, for example, is designed to assist radiologists in the detection of solid pulmonary nodules, while syngo LungCARE
CT is a tool to support physicians in confirming the presence or
absence of lung lesions and to provide automatic segmentation and
volumetric measurements of lung lesions.
Wish lists for CAD
CAD established as a permanent fixture in the radiology toolset, many
radiologists are looking toward the future and have identified areas
where they would like to see improvements. Dr. Destounis, for one,
expressed a desire for CAD systems that provide “[i]mproved specificity,
less false positives, [and] only show marks for cancer or identify
which abnormalities are the more serious ones so I can pay more
attention to them.” In addition, she said she would like to see temporal
comparisons of CAD over years screened. “If we could do temporal
comparisons, we may be able to identify any subtle change in the films
over years,” she said. “I think CAD has a lot of information to give us,
and we should be able to capture this information and review it for
each patient.” An important advancement for CAD for breast MRI,
according to Dr. Shermis, would be the capability to distinguish whether
an abnormality is new. “It may be helpful to show if a finding were
different from prior findings. CAD for MRI, for my personal preference,
may be better for postprocessing when there is patient movement—when it
looks like an enhancing lesion, but is really not an enhancing lesion,”
The takeaway message from Dr. Destounis is that CAD “is
not supposed to replace the radiologist, yet it is helpful, and it can
always get better.”
- Rao VM, Levin DC, Parker L, et al. How widely is computer-aided detection used in screening and diagnostic mammography? J Am Coll Radiol. 2010;7:802–805.
- Fenton JJ, Abraham L, Taplin SH, et al. Effectiveness of computer-aided detection in community mammography practice. J Natl Cancer Inst. 2011:103;1152-1161.
- National Cancer Institute. Chest x-rays can detect early lung cancer but also can produce many false-positive results. J Natl Cancer Inst. http://www.cancer.gov/newscenter/ pressreleases/2005/plcolungbaseline. Accessed August 29, 2011.
- The National Lung Screening Trial Research Team. Reduced lung-cancer mortality with low-dose computed tomographic screening. N Engl J Med. 2011;365:395-409.
- Largest randomized lung cancer screening trial demonstrates screening with low-dose CT reduces lung cancer deaths. American College of Radiology. http://www.acr.org/ HomePageCategories/News/ACRNewsCenter/NLST-Results.aspx. Updated June 29, 2011. Accessed August 31, 2011.