Faculty Bibliography

PURPOSE: To investigate the MRI characteristics of an intracellular manganese-based contrast agent, EVP 1001-1 (Eagle Vision Pharmaceutical Corp.), in a canine model of myocardial infarction. MATERIALS AND METHODS: Three dogs were imaged 14-37 days following permanent ligation of the left anterior descending coronary artery (LAD). Measurements of the longitudinal relaxation rate R(1) were made prior to EVP 1001-1 administration (20 micromol/kg i.v.) and for one hour thereafter. Triphenyl tetrazolium chloride (TTC) staining was used to document infarction. RESULTS: In normal myocardium, EVP 1001-1 produced a substantial increase in the longitudinal relaxation rate, which remained fairly constant over the postcontrast imaging period (DeltaR1= 1.47 +/- 0.58 sec(-1) (mean +/- SD) at 35 minutes, P < 0.05). In the infarct, the response to EVP 1001-1 was small or negligible (DeltaR1= 0.27 +/- 0.28 sec(-1)). This resulted in a significant postcontrast difference in relaxation rate between normal and infarcted tissue (R1(normal) - R1(infarct) = 1.08 +/- 0.26 sec(-1), P < 0.05). The infarct remained clearly delineated in all animals throughout the steady-state imaging period, and qualitatively matched TTC results. CONCLUSION: The persistent enhancement pattern revealed by MRI following EVP 1001-1 administration may be beneficial for identifying and characterizing myocardial infarction

PURPOSE: To investigate the tendency of proton MR signal intensity (SI) gradients to be steeper in the supine than in the prone body position, and to quantify the relation between gravity-related and isogravitational changes of SI on proton MR images of the lung. MATERIALS AND METHODS: In eight healthy volunteers, MR images were obtained in the supine and prone positions using a multiple inversion recovery turbo spin-echo (TSE) sequence. The variation in SI along the gravity-dependent direction and within isogravitational planes was measured on a pixel-by-pixel basis. Ratios of slopes were calculated for comparisons among volunteers. Comparisons of ratios were made using Fisher's exact test. Isogravitational variability was compared with the mean SI, the signal-to-noise ratio (SNR), and the image noise. RESULTS: The average ratios of slopes showed that the overall SI gradient was steeper in the supine than the prone position, with a substantial difference in the supine/prone ratios between inspiration (1.21) and expiration (1.72). In both the supine and prone positions, gravity-dependent gradients were steeper in expiration than in inspiration (P = 0.001). The SI variability along the gravitational direction was larger than the isogravitational variability. The isogravitational variability in turn was larger than the image noise but smaller than the mean SI of the MR images. CONCLUSION: Gravity-dependent gradients in proton MR SI are steeper in the supine than in the prone position. The magnitudes of these gradients were larger than the isogravitational signal variability, showing that MRI is sensitive to gravitationally induced effects

A method for estimating T1 using a single breath-hold, segmented, inversion recovery prepared, true fast imaging with steady-state precession (sIR-TrueFISP) acquisition at low flip angle (FA) was implemented in this study. T1 values measured by sIR-TrueFISP technique in a Gd-DTPA-doped water phantom and the human brain and abdomen of healthy volunteers were compared with the results of the standard IR fast spin echo (FSE) technique. A good correlation between the two methods was observed (R2=0.999 in the phantom, and R2=0.943 in the brain and abdominal tissues). The T1 values of the tissues agreed well with published results. sIR-TrueFISP enables fast measurements of T1 to be obtained within a single breath-hold with good accuracy, which is particularly important for chest and abdominal imaging

Diffusion tensor imaging (DTI) was used to derive in vivo tissue status measurements of subcortical brain regions that are vulnerable to injury in human immunodeficiency virus (HIV)-infected patients. Quantitative measurements, including the mean diffusivity (MD) and fractional anisotropy (FA), were determined in lateralized basal ganglia (caudate and putamen) and centrum semiovale in 11 well-characterized HIV patients and in 11 control subjects. DTI measurements were examined for patterns of relationship with markers of clinical and cognitive progression. DTI measures acquired in subcortical regions were significantly correlated with loss of function in specific cognitive domains. Significant relationships were identified between measures for putamen and verbal memory (MD), visual memory (FA), working memory (FA), and overall cognitive impairment (MD). Measures for caudate (FA) were significantly correlated with visual memory. Measures for centrum semiovale were significantly correlated with visual memory deficits (MD) and visuoconstruction (FA). Relationships between anisotropy measures and anemia (basal ganglia) and CD4 counts (centrum semiovale) were also observed. Findings from this investigation indicate that DTI is a sensitive tool for correlating neuroanatomic pathologic features with specific cognitive deficits in patients with HIV infection.

PURPOSE: To demonstrate a differential response following administration of a free radical scavenger, tempol, in kidneys of hypertensive compared to normotensive rats. MATERIAL AND METHODS: Data were obtained in spontaneously hypertensive rats (SHR, N = 5). Wistar-Kyoto rats (WKY, N = 6) were used as normotensive controls. RESULTS: Consistent with prior reports, SHRs show a significant response to tempol (R(2)*decreased from 40.56 +/- 0.66 second(-1) to 28.58 +/- 0.6 second(-1) in medulla, P < 0.05), while WKY rats exhibit a minimal change (R(2)* measuring 22.36 +/- 4.38 second(-1) pre-tempol and 21.57 +/- 4.78 second(-1) post-tempol, in medulla). The post-tempol R(2)* in SHR was found to be comparable to pre-tempol values in WKY rats, suggesting an improved medullary oxygenation in SHRs. CONCLUSION: Based on both baseline R(2)* values and the differential effect of the free radical scavenger on renal medullary oxygenation, BOLD MRI can distinguish hypertensive from normal kidney in rats

BACKGROUND AND PURPOSE: Quantitative MR imaging strategies may have considerable potential for in vivo assessment of neuropathologic changes associated with HIV. This investigation evaluated the prognostic significance of whole brain histogram-derived diffusion tensor imaging indices with respect to severity of cognitive impairment and measures of clinical status in cases of HIV. METHODS: Quantitative indices derived with diffusion tensor imaging, including whole brain fractional anisotropy and the apparent diffusion coefficient, were compared for six patients with HIV and eight control volunteers. Relationships between whole brain indices and specific measures of dementia severity and clinical status were examined. RESULTS: Whole brain fractional anisotropy was reduced in patients with HIV and was significantly associated with severity of dementia, as indicated by several widely used clinical and functional status measures. Summary fractional anisotropy measures were more prognostic of dementia status than were apparent diffusion coefficient measures. CONCLUSION: Findings from this investigation support the use of diffusion tensor imaging for noninvasive MR imaging measurement of neuropathologic changes in studies of HIV-associated cognitive impairment.

Steady-state free precession (SSFP) cardiac cine images are frequently corrupted by dark flow artifacts, which can usually be eliminated by reshimming and retuning the scanner. A theoretical explanation for these artifacts is provided in terms of spins moving through an off-resonant point in the magnetic field, and the theory is validated using phantom experiments. The artifacts can be reproduced in vivo by detuning the center frequency by an amount in the range of half the inverse repetition time (TR). Since this offset is similar in magnitude to the frequency difference between the water and lipid peaks, a likely cause of the artifacts in vivo is that the center frequency is tuned incorrectly to the lipid peak rather than the water peak

Use of a parallel imaging technique to improve temporal and spatial resolution at three-dimensional contrast-enhanced magnetic resonance (MR) angiography was investigated. Thirty experiments were performed in five groups of healthy subjects. In groups 1-3, the technique was used to improve imaging speed by a factor of two or four while maintaining spatial resolution. Contrast agent concentration was two to four times higher than at standard MR angiography, to take advantage of the faster imaging speed. In groups 4 and 5, the technique was used to double spatial resolution in the phase-encoding direction while maintaining imaging speed and contrast agent concentration. At a two to four times faster imaging speed, signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) almost equaled those at standard MR angiography, likely a result of increased contrast agent concentration. The use of parallel imaging to achieve higher spatial resolution was also proved feasible, but with substantial reduction in SNR and CNR

PURPOSE: To estimate the reproducibility of BOLD MRI measurements in the evaluation of intrarenal oxygenation levels. MATERIALS AND METHODS: In this study, the reproducibility of semiquantitative BOLD MRI measurements performed on a 1.5 T scanner with a multiple gradient-echo sequence in the renal medulla and cortex, and their response to furosemide and waterload, were assessed in eight healthy young subjects (25.6 +/- 4.1 years). Each subject underwent an identical experimental procedure on two separate days. RESULTS: Renal R2* measurements were shown to be reproducible within approximately 12% from day to day based on a coefficient of variance (CV) analysis. The changes in R2* (DeltaR2*) following administration of furosemide were statistically significant, as shown by ANOVA and a paired Student's t-test, and were deemed reliable based on the reliable change index (RCI). However, DeltaR2* values following waterload were not statistically significant, and were not deemed reliable. CONCLUSION: R2* measurements were reproducible over 270 days within 12%. Furosemide produced a significant and reliable change (approximately 30%), and the magnitude of change (5.7 s(-1)) was reproducible and consistent with our previous data. The response to waterload, however, did not reach statistical significance, and the magnitude did not reach the level that we had previously reported

PURPOSE: To test the hypothesis that, in magnetic resonance (MR) imaging of healthy individuals, equal relative changes in lung volume cause equal relative changes in MR signal intensity of the lung parenchyma. MATERIALS AND METHODS: In two experimental runs, 10 volunteers underwent spirometrically monitored MR imaging of the lungs, with MR images acquired at 10 incremental lung volumes ranging from total lung capacity to 10% above residual volume. Average signal intensity, signal variability, and signal intensity integrals were calculated for each volunteer and for each lung volume. The effect of lung volume on signal intensity was quantified using linear regression analysis complemented by the runs test. Slopes and intercepts of regression lines were compared with an analysis of covariance. Slopes of the lines of best fit for lung volumes and signal intensities from the two runs were compared to the slope of the line of identity. Comparisons between the two runs were visualized using Bland and Altman plots. RESULTS: The slopes of the 10 individual regression lines yielded no significant differences (F = 1.703, P = 0.101; F = 1.321, P = 0.239). The common slopes were -0.556 +/- 0.027 (P = 0.0001) for the first and -0.597 +/- 0.0031 (P = 0.0001) for the second experimental run. Both slopes displayed no significant nonlinearity (P = 0.419 and P = 0.067). There was a strong association between changes in lung volumes (rs = 0.991, P = 0.0001) and changes in signal intensity (rs = 0.889, P = 0.0001) in the two experimental runs. Lines of best fit for lung volume and signal intensities were not significantly different from the slope of the line of identity (P = 0.321 and P = 0.212, respectively). CONCLUSION: Equal changes in lung volume cause equal changes in MR signal intensity of the lung parenchyma. This linear and reproducible phenomenon could be helpful in comparing pulmonary MR signal intensity between individuals