Presented at the UCSF Department of Radiology Progress in Radiology conference series Presentation date: May 30, 2001 in HSW-301

 

Presenter: Miriam A. Bredella, MD, PhD
Abstract Title: Use of FDG-PET and MR Imaging for Evaluating Therapy Response in Musculoskeletal Sarcomas
Authors: Miriam A. Bredella, MD, PhD, Gary R. Caputo, MD, James O. Johnston, MD, Lynne S. Steinbach, MD
Abstract:
Purpose: To investigate the potential of FDG-PET to distinguish viable tumor from post-therapeutic changes in areas of equivocal MR imaging findings in patients with musculoskeletal sarcomas.

Materials and Methods: The study group comprised 12 patients (8 men, 4 women, aged 9-53y, mean age 23y) with a history of bone or soft-tissue sarcoma who had undergone various treatments (surgery, chemo-, or radiation therapy) and presented with clinically suspected recurrent or residual tumor. All patients underwent Gd-DTPA-enhanced MR imaging and whole body FDG-PET. Imaging results were correlated with histologic findings and/or clinical long term follow-up.

Results: In nine patients MR imaging findings were equivocal in differentiating between post-therapeutic changes and tumor recurrence. Subsequent FDG-PET demonstrated increased uptake, consistent with recurrent tumor in five cases. This was confirmed by biopsy. Four patients showed no increased uptake on FDG-PET and were closely monitored clinically. No tumor recurrence was found in these patients. One patient demonstrated MR imaging findings of recurrent tumor that was confirmed by FDG-PET and histology. Two patients underwent limb salvage procedure prior to MR imaging and MR images were deemed inadequate for interpretations secondary to extensive metallic artifacts. In these cases FDG-PET was helpful in the evaluation of tumor recurrence.

Conclusion: FDG-PET provides an useful adjunct tool to MR imaging in distinguishing viable tumor from post-therapeutic changes in patients with bone and soft tissue sarcomas.

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Presented at the UCSF Department of Radiology Progress in Radiology conference series Presentation date: May 30, 2001 in HSW-301

 

Presenter: Benjamin M. Yeh, MD
Abstract Title: Comparison of Gadolinium-enhanced 3D MRA and 3D Reconstructions with Spin-Echo MRI for Coarctation of the Aorta.
Authors: Benjamin M. Yeh, MD, Gautham P. Reddy, MD; Ming Yang, MD; Michael B. Gotway, MD; Daniel N. Heller, MD, MS; Charles B. Higgins, MD
Abstract:
PURPOSE: Prior reports have demonstrated the accuracy of spin echo MRI for evaluation of the severity of coarctation of the aorta. The purpose of this study was to compare contrast-enhanced 3D MRA to spin echo MRI for assessment of coarctation severity.

METHOD AND MATERIALS: We performed MRI on 20 patients to assess for coarctation of the aorta. Eleven of the patients had prior surgical coarctation repair. All patients underwent ECG-gated spin echo MRI as well as gadolinium enhanced breathhold 3D MRA. We reconstructed the MRA data into whole volume maximum intensity projection (MIP), volume rendered (VR), and thin sliding maximum intensity projection (thin MIP) images. Each image set was reviewed independently by 2 blinded observers (reader A and reader B). Severity of stenosis was defined as the diameter of the narrowest segment of the aorta divided by that of the descending aorta. Stenosis of at least 40% was considered to be anatomically significant. As a standard of reference, in 15 examinations we assessed functional significance of the coarctation by comparing flow in the proximal descending aorta and distal descending aorta using velocity-encoded cine (VEC) MRI. RESULTS: For reader A the mean percent stenosis defined by each technique and reconstruction was similar. For reader B, thin MIP underestimated the severity of the coarctation compared to the other sequences. In general, there was good agreement between readers for mean stenosis for each sequence, except for thin MIP where there was significant difference between the readers. Comparing each imaging technique with spin echo MRI, the MIP and volume rendered images showed the best correlation. Using VEC MRI as a gold standard for hemodynamically significant coarctation, all imaging techniques and reconstructions show 100% specificity. The least variability and greatest overall sensitivity were seen with spin echo MRI and MIP reconstruction.

CONCLUSIONS: Whole volume MIP and volume rendered images correlate most closely with spin echo MRI for evaluation of anatomic severity of coarctation. The specificity for detecting anatomically hemodynamically significant stenosis was 100% for all sequences compared with velocity encoded cine MRI. Spin echo and MIP MRA show the highest overall sensitivity and the best reproducibility for detecting anatomically significant stenosis.

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Presenter: Tuong Huu Le, M.D., Ph.D.
Abstract Title: Functional MRI of Human Auditory Cortex Using Block and Event-Related Designs
Authors: Tuong Huu Le, Sandy Patel, Timothy P. L. Roberts
Abstract:
PURPOSE: Functional MRI studies of the human auditory cortex using block and two event-related designs were compared. The ability of fMRI to resolve the tonotopic organization was evaluated.

METHODS: Nine healthy adult volunteers participated in the study. Pure tones (900ms duration; 200Hz, 1000HZ, and 3000Hz; 70 dB SPL) were presented mono-aurally to the right ear. Axial gradient-echo EPI images (GE-LX2 1.5T, TE = 69ms,  = 90 degrees, in-plane resolution = 1.56mm x 1.56mm, slice thickness = 5mm) were acquired through the Heschl's gyrus. Gradient switching noises were attenuated by 60-65 dB when using earmuffs in combination with ear foam inserts. The effect of gradient noises was eliminated in the silent event-related (sEfMRI) design by using a long TR. Block design (# slices = 7, TR = 2s, ISI = 1.1s), sEfMRI design (# slices = 4, TR = 20s, ISI = 20s), and conventional event-related (cEfMRI) design (# slice = 1, TR = 1.5s, ISI = 30s) were compared. Images were compensated for gross motion artifacts using the automated image registration (AIR) method. Actiation maps were created using t-test. Sources of activation were defined as the center of a four-voxel cluster with the highest statistical significance (p<0.01).

RESULTS: Based on the cEfMRI study, the average duration of the BOLD response was 4.2, 3.8, and 4.2s for 200, 1000, and 3000Hz tones, respectively. The corresponding average times for the BOLD signal to reach peak intensity were 4.9, 4.5, and 4.9s; and the average times for the BOLD response to return to baseline were 13.9, 13.6, and 14.8s. The mean signal-to-standard deviation ratio for the sEfMRI study was 40:1. Empirically derived Z scores in the sEfMRI design revealed that 6 averages were required to detect a 5% signal change with a 99% confidence, and 26 averages were required to detect a 2% signal change with the same confidence. Block design failed to demonstrate tonotopy, but both event-related designs provided statistical significant evidence for tonotopy when the stimulus frequencies were about 4 octaves apart. Low frequency (200Hz) tones were more laterally represented than high frequency (3000Hz) tones in both cEfMRI (p=0.04) and sEfMRI (p=0.04) designs. The cEfMRI design also demonstrated anterior-posterior orientation from 200Hz to 3000Hz tones (p=0.05). The tonotopic separation between 200Hz and 1000Hz tones in the sEfMRI designs reached near statistical significance (p=0.08).

CONCLUSIONS: Event-related design was superior to block design in the evaluation of tonotopy. The sEfMRI design provided the best spatial specificity and was immune to the effects of scanner noises.

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