Jane Lowers

Under the best of circumstances, 3T imaging of the prostate with a body coil can approximate the level of detail and sensitivity available at 1.5T with an endorectal coil. Researchers hope that with a 3T-oriented endorectal coil they will finally be able to take advantage of 3T's higher resolution in a challenging portion of the anatomy.

Three studies presented at the ECR Sunday morning compared 1.5T and 3T imaging, and, overall, the researchers gave the nod to 1.5T, based on coil availability. Dr. Dirk Beyersdorff from Charité Hospital in Berlin imaged 24 patients at both field strengths, comparing an endorectal coil at 1.5T with a body coil at 3T. The 1.5T images were clearer, and peripheral and extracapsular lesions were easier to identify consistently.

"Until a 3T coil is available, 1.5T will remain the gold standard," Beyersdorff said. "The endorectal coil is the most important advancement we are waiting for."

A similar study of 30 patients at the University of Modena, Italy, found that 1.5T imaging could identify six of seven extracapsular tumors, compared with five of seven for 3T. The overall sensitivity and specificity for 1.5T were 85% and 83%, respectively, compared with 71% and 83% for 3T. 

Commercial release of a 3T endorectal coil from Medrad is expected later this year, said session moderator Dr. Hedvig Hricak, chair of radiology at Memorial Sloan-Kettering Cancer Center. At the University of Nijmegen, Netherlands, which has worked with an experimental version of the coil, sensitivity for prostate masses increased from 68% to 87% for experienced readers, according to lead researcher Dr. Jurgen Fütterer. 

Despite the presumed clarity of 3T endorectal coil imaging, it won't be the answer for everything, Hricak said. While it may serve an important role in initial staging, body coil imaging will be the preferred technique for planning and monitoring radiation therapy so that the coil does not interfere with mapping the shape and location of the prostate and surrounding tissue.

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Prostate imagers await 3T endorectal coils

Whether it scans in four slices or 16, CT is the method of choice for detecting pulmonary emboli, researchers said at the RSNA meeting. Even four-slice technology boasts a negative predictive value greater than 99%, better than ventilation/perfusion (V/Q) studies or conventional pulmonary angiography. 

Differences among four-, eight-, and 16-slice scanners appear marginal so far, but few data are available to solidify any claims of superiority for 16, except in speed. Researchers at Stanford University clocked lung scan times at 26.6 seconds for four-slice, 9.25 seconds for eight-slice, and 5.45 seconds for 16.

Dr. Alessandro Napoli and colleagues at Stanford reviewed CT studies for 1240 consecutive patients referred for suspected pulmonary emboli. Overall, 20% of cases were deemed positive, with 41% of emboli found in the segmental arteries, 27% in lobal regions, 17% in subsegmental arteries, and 15% on the main branches. 

While there was no statistically significant difference in detection rates among the three generations of scanners, readers said that eight- and 16-slice studies yielded more and clearer diagnostic data. The 16-slice scanner may eventually prove better at finding subsegmental emboli, but only a small number of cases were included in the study.

If a CT study is negative, it is safe to forgo further examination. Researchers at the University of South Carolina conducted a metastudy of 14 published papers with 3283 patients who had undergone CTA to evaluate suspected pulmonary emboli, had negative findings, and had stopped anticoagulation therapy based on those findings. Fourteen developed fatal pulmonary embolism, 23 demonstrated nonfatal embolism, and 52 showed evidence of deep venous thrombosis during follow-up. 

The studies produced 95% to 100% negative predictive value (NPV), with an average of 99.1%. NPV for mortality was 99.4%. Whether the CTAs were performed on single-slice or multislice CT made no significant difference. By comparison, conventional pulmonary angiography has an NPV of 98.4%, and V/Q studies average 88%.

Whether it scans in four slices or 16, CT is the method of choice for detecting pulmonary emboli, researchers said at the RSNA meeting. Even four-slice technology boasts a negative predictive value greater than 99%, better than ventilation/perfusion (V/Q) studies or conventional pulmonary angiography.

Report from RSNA: CTA nails down role of gold standard for pulmonary embolism

How well a patient can count, remember word lists, or perform other basic tests may not indicate how far Alzheimer's dementia has progressed biologically, researchers said at the RSNA meeting. 

The Mini-Mental Status Exam has been the standard diagnostic tool for Alzheimer's disease for years, relying on a series of simple cognitive tests to calculate a score for degree of mental impairment. In 58 patients who also underwent PET or SPECT imaging, however, the MMSE showed little correlation with imaging evidence of advanced disease. 

Many patients with near-normal MMSE scores showed pronounced bilateral defects on imaging, while others with extremely low MMSE scores showed only moderate PET or SPECT perfusion defects, according to Amitha Rao, a third-year medical student at the University of Kansas, who completed the research under the direction of radiologist Dr. Reginald Dusing.

Patients were excluded from the study if they showed evidence of non-Alzheimer's dementias, vascular defects, or other conditions that could mimic symptoms or invalidate imaging findings. Two readers, board-certified in both radiology and nuclear medicine, interpreted the studies.

The lack of correlation between the two types of tests adds muscle to the theory that adding PET or SPECT may speed the diagnosis of Alzheimer's, Rao said. 

PET has secured limited Medicare reimbursement as an imaging agent in dementia cases, but only to rule out non-Alzheimer's dementias that can not be distinguished clinically from Alzheimer's. 

How well a patient can count, remember word lists, or perform other basic tests may not indicate how far Alzheimer's dementia has progressed biologically, researchers said at the RSNA meeting.

Report from RSNA: PET, SPECT findings challenge office test results for Alzheimer's disease

Breast tomosynthesis may be a work-in-progress in the RSNA exhibit halls, but researchers are already considering ways to incorporate computer-assisted detection algorithms to improve its efficacy.

Researchers from the University of Chicago and the University of Michigan presented papers Tuesday morning that evaluated several techniques for reconstructing suspected tumors from the multiple slices of tomographic acquisition or from the compiled volume data set. Both groups worked with the GE Digital Breast Tomosynthesis prototype developed by Dr. Daniel Kopans at Massachusetts General Hospital.

The Michigan researchers produced an area of 0.87 under the ROC curve with 80% sensitivity and two false positives per case, using a set of synthesized data. Looking only at projection views, the area under the ROC curve dropped to 0.82. Both were based on 26 cases with 23 masses, including 13 malignancies. 

"We achieved fewer false positives with 3D views than with 2D, and the information fusion is more effective," said lead researcher Heang-Ping Chan, Ph.D.

Chicago researchers evaluated only projection views. A standard tomosynthesis scan involves 11 low-dose conebeam projections through the breast at 5-degree angles spread over an arc. The projections intersect with each other at various points and allow the software to confirm areas of suspected masses from more than one angle. For the Chicago trial, any region that was intersected by six or more projections was considered a positive finding. Among 21 cases of confirmed breast masses, the team achieved a sensitivity of 86%, but with six false positives per case.

In addition to projection views and reconstructed volumes, CAD could also be developed to look for suspicious findings across the 50 to 80 reconstructed image slices that could be produced for each set of breast data, the authors said.

Jane Lowers

Articles

Prostate imagers await 3T endorectal coils

Report from RSNA: CTA nails down role of gold standard for pulmonary embolism

Report from RSNA: PET, SPECT findings challenge office test results for Alzheimer's disease

Breast tomosynthesis attracts CAD research