Faculty Bibliography

RATIONALE AND OBJECTIVES: To investigate the potential of a novel manganese-based magnetic resonance (MR) contrast agent, EVP 1001-1 for the evaluation of myocardial ischemia. METHODS: MR imaging with EVP 1001-1 was performed on 6 Yorkshire pigs, and T1 relaxation times were calculated. One animal served as a control, 2 were subjected to an acute coronary artery occlusion and 3 provided a model of chronic ischemia. RESULTS: Administration of the agent in the control and acute coronary occlusion model demonstrated a short plasma half-life (approximately 1.5 minutes) and rapid myocardial uptake in nonoccluded regions, with long retention times in the myocardium (>1 hour) and no evidence of redistribution. In the chronic ischemia model, differential enhancement was observed between normal and ischemic tissue, particularly under dobutamine-induced stress. CONCLUSIONS: These properties suggest the use of EVP 1001-1 for steady-state imaging of myocardial perfusion. Contrast administration could be performed under stress conditions outside the scanner, with high-resolution MR images reflecting the stress condition acquired after the stress has subsided

PURPOSE: To examine whether the noninvasive technique of blood oxygenation level dependent magnetic resonance imaging (BOLD MRI) can detect changes in renal medullary oxygenation following administration of a nitric oxide (NO) synthase inhibitor, N(G)-nitro-L-arginine methyl ester (L-NAME). Hypertension is associated with endothelial dysfunction and is characterized by a lack of response to endothelial-dependent vasoactive substances, including nitric oxide synthase inhibitors. We hypothesized that the magnitude of the change would be reduced in the kidneys of hypertensive subjects relative to normal controls. MATERIALS AND METHODS: To test this hypothesis, data were obtained in spontaneously hypertensive rats (SHR, n = 6). Wistar-Kyoto rats (WKY, n = 7) were used as normotensive controls. RESULTS: As expected, WKY rats showed a significant response to L-NAME (R(2)* increasing from 23.6+/-1.5 Hz to 32.5+/-2.2 Hz, P < 0.05), while SHR exhibited a minimal change in medullary oxygenation (R(2)* measuring 31.9+/-2.8 Hz pre- and 35.5+/-2.2 Hz post-L-NAME). The baseline R(2)* in SHR is found to be comparable to post-L-NAME values in WKY rats, suggesting a basal deficiency of nitric oxide in SHR. CONCLUSION: Based on the differential effect of NO synthase inhibition on medullary oxygenation, BOLD MRI can distinguish hypertensive from normal kidney. Our results are consistent with previously reported observations using invasive methods

PURPOSE: To evaluate the T1 efficacy of EVP-ABD, a new manganese (Mn)-based contrast agent, for vascular and liver tissue enhancement in comparison with currently approved agents. MATERIALS AND METHODS: Ten Yorkshire pigs (body weight, 26 -46 kg) were used for the efficacy evaluation, nine for kinetic T1 evaluation (three each agent) and one for post EVP-ABD imaging. With a fast imaging scheme to monitor T1 values of blood and liver, 10 micromol/kg EVP-ABD was injected intravenously and compared with gadopentetate dimeglumine (Magnevist, GdDTPA) and mangafodipir trisodium (Teslascan, mangafodipir trisodium) at routine clinical dosages. All were imaged with 3D T1 Gradient Recalled Echo (GRE) sequence (TR/TE/alpha = 3.8/1.6/25 degrees ) prior to and 10 minutes post injection using a 1.5-T whole-body scanner. Additional high-resolution 2D liver images (TR/TE/alpha = 50/4.6/40 degrees ) and arterial phase images of the upper aorta were acquired from the pig for post EVP-ABD imaging. RESULTS: At 10 micromol/kg, EVP-ABD provided a dramatic decline in blood T1, comparable to 0.1 mmol/kg GdDTPA, followed by a rapid return to blood baseline T1 values. In addition to the blood enhancement phase, EVP-ABD achieved a 70% reduction in liver T1 within 2 minutes postadministration, with an imaging window of at least 2 hours. A substantially improved signal-to-noise ratio (SNR) was observed in both the 2D and 3D liver images postcontrast. CONCLUSION: EVP-ABD demonstrated peak vascular enhancement similar to GdDTPA and prolonged specific liver enhancement exceeding mangafodipir trisodium. EVP-ABD has favorable T1 enhancing characteristics with the potential to allow for a comprehensive liver evaluation

Band artifacts due to bulk motion were investigated in images acquired with fast gradient echo sequences. A simple analytical calculation shows that the width of the artifacts has a square-root dependence on the velocity of the imaged object, the time taken to acquire each line of k-space and the field of view in the phase-encoding direction. The theory furthermore predicts that the artifact width can be reduced using parallel imaging by a factor equal to the square root of the acceleration parameter. The analysis and results are presented for motion in the phase- and frequency-encoding directions and comparisons are made between sequential and centric ordering. The theory is validated in phantom experiments, in which bulk motion is simulated in a controlled and reproducible manner by rocking the scan table back and forth along the bore axis. Preliminary cardiac studies in healthy human volunteers show that dark bands may be observed in the endocardium in images acquired with nonsegmented fast gradient echo sequences. The fact that the position of the bands changes with the phase-encoding direction suggests that they may be artifacts due to motion of the heart walls during the image acquisition period

Magnetic resonance ventilation-perfusion (V/Q) imaging has been demonstrated using oxygen and arterial spin labeling techniques. Inhaled oxygen is used as a paramagnetic contrast agent in ventilation imaging using a multiple inversion recovery (MIR) approach. Pulmonary perfusion imaging is conducted using a flow-sensitive alternating inversion recovery with an extra radiofrequency pulse (FAIRER) technique. A half Fourier single-short turbo spin echo (HASTE) sequence is used for data acquisition in both techniques. V/Q imaging was performed in ten of the twenty volunteers, while either ventilation or perfusion was imaged in the other ten. This V/Q imaging scheme is completely noninvasive, does not involve ionized radiation, and shows promising potential for clinical use in the diagnosis of lung diseases such as pulmonary embolism