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November 19 , 2007

Computer Assist — MRI CAD and Cancer Detection
By Kathy Hardy
Radiology Today
Vol. 8 No. 23 P. 34

Early breast cancer detection through screening is known to reduce mortality rates. The treatment of prostate cancer, the second leading cause of cancer death in men, can be less invasive and more exact than ever before. The revolutionary modality enabling patients with these two types of cancer to share similar success stories is computer-enhanced imaging—MRI combined with computer-aided detection (CAD) software.

Breast MRI has been used as an alternative to mammography for the past 15 years. Studies from the early 1990s show that MRI detected more cancerous lesions than mammography. Used more prevalently in the past five years, advanced breast MRI enables radiologists to image both breasts simultaneously. High spatial resolution, thin section imaging is performed and requires both a dedicated bilateral breast coil and a high field-strength magnet. These technical parameters are considered to be the minimal requirements to perform an adequate breast MRI study. Overall, breast MRI is considered more sensitive than mammography.

The False Positive Problem
However, according to David R. Gruen, MD, a radiologist and assistant chief of the medical staff at Norwalk Hospital in Connecticut, it is that high level of sensitivity that can result in more false positives and require biopsies for confirmation as to whether a lesion is malignant or benign.

“The difference between mammography and breast MRI is that from breast MRI, we get detailed information about how a lesion enhances, not just how it looks,” Gruen says. “With MRI, we evaluate the morphology—what a lesion looks like—in great detail. We also evaluate how it takes up contrast and how that contrast leaves the lesion—its ‘kinetics.’ If a lesion looks bad or enhances in a suspicious way, our attention is called to the lesion. All this information goes into reaching a conclusion as to what’s good and what isn’t. With CAD, we can better, more accurately, and more quickly analyze what we find. This is the wave of the future as imaging becomes more sensitive.”

The screening process for prostate MRI also becomes more specific with CAD, but the chances of a false positive diagnosis are less likely than with breast MRI.

“The nature of breast tissue allows for the potential development of more lesions that can enhance,” says A. Joseph Borelli, Jr, MD, president and medical director at MRI at Belfair in Bluffton, S.C. “In the prostate gland, there are fewer pathologies that will enhance. Essentially, if you see something in the peripheral zone of the prostate gland that enhances preferentially (ie, more rapidly than surrounding tissue), it is almost always malignant.”

With prostate screening, MRI is considered a sensitive tool for the noninvasive evaluation of cancer. Once a patient has been diagnosed with prostate cancer, MRI is used for staging and determining the extent of the disease.
“Because of its low cost and high sensitivity, the prostate-specific antigen [PSA] test is a good screening tool for prostate cancer,” Borelli says. “If the PSA level comes back elevated, then the patient typically undergoes a biopsy. MRI is prescribed after the biopsy for the staging of the cancer and evaluation for minimally invasive therapy.”

Improving Specificity
Determining a lesion’s behavior is where something such as CAD comes in. Confirma Inc.’s CADstream analysis software adds a level of specificity to MRI screening. CADstream automatically creates lesion characterizations with 3D renderings and data calculations for each lesion within the study. CADstream enables radiologists to see 3D renderings of volumes, lesion diameter measurements, lesion location, automatic detection of curves within the volume, and morphology characterizations. With CADstream, image processing and analysis functions currently performed manually by an MRI technologist and radiologist are automated. All processed data are saved and presented with the original images for radiologist interpretation.

Breast MRI specialists were early adopters of CAD technology. With CAD, a heightened level of specificity works to assist radiologists in determining whether a lesion found by the highly sensitive MRI screening process is malignant or benign.

With CAD, screeners are looking for a cell pattern or array that is indicative of cancer. Unlike CAD for mammography, CAD for MRI doesn’t “flag” anything, Gruen says. “It really functions as a ‘computer-aided visualization’ tool by postprocessing the data to compare pixel signal intensity values before and after contrast,” he says. “CAD allows us to more accurately and reproducibly evaluate how lesions enhance and washout, which are markers of potential cancers.”

With the CAD process, different types of lesions turn different colors. Red indicates a washout pattern of enhancement, blue persistent enhancement, and yellow plateau enhancement. “You can see what the kinetics of a lesion are by the color,” Gruen says. “CAD with MRI identifies everything in the breast and identifies what the enhancement looks like.”

Prostate Applications
Each MRI consists of 2,000 to 3,000 images. “So if you’ve completed 10 MRIs in a day, that’s 20,000 to 30,000 images to review,” Gruen says. “How do you review and manage this huge amount of data? How do you monitor the changes that may occur from month to month and evaluate which are clinically significant? CADstream gives you the ability to manage all the data.”

With prostate MRI, “You need analysis of the rate of initial enhancement vs. the rate of latent enhancement,” Borelli adds. “To do this manually is almost impossible. CAD gathers data on a pixel-by-pixel basis for the prostate gland. Then it registers the data in 3D to eliminate artifacts from motion.”

CAD’s role in prostate MRI differs from breast MRI in that it is meant to confirm where malignant lesions exist in the prostate gland for their effective removal. Identification of malignant lesions when CAD is combined with prostate MRI is 95% accurate, Borelli says.

“This is important,” he says. “The data on where the lesion is located needs to be reliable to make sure when you go in to remove malignant lesions we’re not leaving any cancer behind.”

Down the road, Borelli sees the exact pinpointing of cancerous lesions as vital for doctors to assess alternatives to removing the entire prostate gland. “Much like a lumpectomy can be performed on a woman with breast cancer, we could remove just the malignancy from the prostate gland rather than perform a complete prostatectomy,” he says.

Maintaining a steady imaging process is just as important and can be an issue during a lengthy prostate study, which can take as long as 10 minutes, Borelli says. During that time, a patient can shift and even the slightest movement within proximity of the prostate gland can alter the screening results.

“If the gland should move during the course of screening, a computer with CAD can reregister the data in 3D, basically shifting the gland back into its proper position,” he says. “It makes the data fit properly into the image. You couldn’t do this manually with the data.”

Breast Imaging With CAD
According to Gruen, a particular challenge for interpreting breast MRIs is the assessment of a lesion’s morphologic and kinetic features at multiple imaging series. One key analysis function performed with CAD is automatic kinetic assessment. The detailed information on lesion kinetics provided with computer-aided evaluation generates detailed data for all pixels in the lesion. This differs substantially from data obtained with conventional manual placement of a region of interest, which only provides kinetic information for portions of a lesion.

“Data are postpresented into an easy-to-read format to quickly look at morphology,” he says. “You can see the lesions—look at their shape, size, and location—to see if they are benign. Without CADstream, it’s much more difficult to identify lesions and what the enhancement curves look like. It’s a vital visualization tool in the breast MRI process.”

While MRI is a standard procedure when it comes to treating patients with prostate cancer, breast MRI is not always the first line of defense in the fight against breast cancer. The American Cancer Society (ACS) recommends MRI be used for women with an increased risk of breast cancer and recommends annual screening using MRI in addition to mammography for women with a 20% or greater lifetime risk of the disease.

Based on data gathered since 2003, this includes women with a strong family history of breast or ovarian cancer and women treated for Hodgkin’s disease.

Gruen notes that some women without a family history of breast cancer, particularly those with dense breast tissue that is not easily screened with routine mammography, are also prime candidates for breast MRI. However, with the ACS recommendations based solely on family history, insurance coverage for breast MRI becomes an issue for women with strong individual risk factors, but no family history.

“For women at risk of breast cancer, you need to conduct breast MRI frequently, and you need to have CADstream to interpret the findings accurately,” he says. “Using CADstream can decrease false positives by 25% and results in fewer biopsies.”

Moving Forward
Borelli, who is the chairman of the Committee on MRI Accreditation of the American College of Radiology, notes that his experience with MRI and CAD goes back to its use with breast imaging approximately three years ago. After seeing its success with diagnosing breast cancer, he modified the process to make it applicable to prostate screening nearly eight months ago. Since that time, he has become involved in the research phase of prostate MRI and CADstream and is now conducting clinical evaluation of the Confirma product.

While breast MRI and prostate MRI have taken the lead in the area of CAD implementation, Borelli contends that this is just the beginning. “In my mind, you could apply this technology throughout the body,” he says. “All malignancies have a preferential blood supply, which is what dynamic contrast-enhanced MRI combined with CAD targets.”

— Kathy Hardy is a freelance writer and editor based in Phoenixville, Pa.