Why isnt PEM used instead of MRI for breast cancer detection

Why isn\'t PEM used instead of MRI for breast cancer detection? Are there clear draw backs to PEM vs MRI?

Solution

PEM, the breast application of a high-resolution PET scanner, has emerged since its FDA clearance in 2003 as a viable advanced imaging technique to help with presurgical planning and staging, to evaluate axillary lymph nodes, to monitor response to neoadjuvant chemotherapy and to look for recurrent disease. A biopsy capability using existing MRI vacuum-assisted techniques was approved in 2008 and has a high adoption rate. PEM produces a 3-D tomographic view of the breast in 12 images per view. Early studies comparing the results of PEM with pathology showed a sensitivity of 90 percent as well as a high specificity of 86 percent in evaluating known breast cancer or suspicious lesions. Other studies have shown that PEM has a positive predictive value for biopsy of 83 percent when compared to 74 percent for MRI with no statistically significant difference in sensitivity and specificity. A larger prospective multicenter study showed PEM and MRI to be equally sensitive and specific for detection of primary lesions, but PEM was more specific than MRI for detection of secondary smaller lesions and had a higher PPV. PEM’s higher specificity shows a potential to reduce false positives compared to other advanced breast imaging modalities. PEM requires a high-resolution PET scanner and injection of 5 mCi of 18F-FDG, a minimum of 60-minute uptake time with a fasting glucose level of <140 mg/dl. No specific timing is required, as the radiotracer is not impacted by hormonal perturbations. It should be performed by a dedicated team, which can include either radiologists experienced in mammography and image-guided biopsy techniques or nuclear medicine physicians. The availability of PEM-guided vacuum-assisted biopsy is essential for centers performing PEM to confirm lesions not seen on any other modality, given the scanner’s 1.6 mm resolution. As this technology is PET, new breast cancer-specific radiotracers, such as fluorine-18 16?-fluoroestradiol (FES), and tracers developed to identify proliferating and non-proliferating tumors, like [18F] fluorothymidine (18F -FLT) and Cu-64, are currently used on this device to monitor response to neoadjuvant chemotherapy. These radiotracers are available only in clinical trials under IND in the U.S., but are in clinical use with PEM in other countries. Dose is also a concern with PEM. Since it is typically deployed after an initial diagnosis of cancer, the risk-to-benefit ratio should be adjusted accordingly. Recent studies have validated a reduced dose of 5 mCi of FDG per exam, resulting in 350 mrem of radiation exposure to the patient or about half the average U.S. yearly exposure. Dose to the technologist with PEM is lower than with BSGI/MBI, as patients are imaged post-void, one hour after injection. In the United States, PEM is not currently deployed as a screening tool and may only be used post-diagnosis. BSGI/MBI is often used both pre- and post-diagnosed, and many centers have taken advantage of Henda’s Law to deploy the technology for problem-solving equivocal mammograms in dense-breasted patients.

source: http://www.itnonline.com/article/pros-and-cons-molecular-breast-imaging-tools