We performed technical optimization followed by a pilot clinical study of quiescent-interval single-shot MR angiography for peripheral vascular disease. Quiescent-interval single-shot MR angiography acquires data using a modified electrocardiographic (ECG)-triggered, fat suppressed, two-dimensional, balanced steady-state, free precession pulse sequence incorporating slice-selective saturation and a quiescent interval for maximal enhancement of inflowing blood. Following optimization at 1.5 T, a pilot study was performed in patients with peripheral vascular disease, using contrast-enhanced MR angiography as the reference standard. The optimized sequence used a quiescent interval of 228 ms, a/2 catalyzation of the steady-state magnetization, and center-to-out partial Fourier acquisition with parallel acceleration factor of 2. Spatial resolution was 2-3mm along the slice direction and 0.7-1mm in-plane before interpolation. Excluding stented arterial segments, the sensitivity, specificity, and positive and negative predictive values of quiescent-interval single-shot MR angiography for arterial narrowing greater than 50% or occlusion were 92.2%, 94.9%, 83.9%, and 97.7%, respectively. Quiescent-interval single-shot MR angiography provided robust depiction of normal peripheral arterial anatomy and peripheral vascular disease in less than 10 min, without the need to tailor the technique for individual patients. Moreover, the technique provides consistent image quality in the pelvic region despite the presence of respiratory and bowel motion. Magn Reson Med 63:951-958,

QISS nonenhanced MR angiography offers an alternative to currently used imaging tests for symptomatic chronic lower limb ischemia, for which the administration of iodinated or gadolinium-based contrast agents is contraindicated.

Higher magnetic field strength is beneficial for renal BOLD MRI studies. The cortico-medullary contrast on the R2* map was significantly improved at 3.0 T, with no evidence of increased bulk susceptibility artifacts. Baseline R2* and DeltaR2* in the renal medulla at 3.0 T were both significantly higher compared to our previously reported data obtained at 1.5 T.

Institutional review board approval and informed consent were obtained for this HIPAA-compliant study, whose purpose was to prospectively evaluate the use of a dual-contrast mechanism in conjunction with an iron oxide blood pool contrast agent, ferumoxytol, to depict deep venous thrombosis (DVT). Nine patients with lower extremity DVT detected with duplex ultrasonography (US) were imaged with magnetic resonance (MR) imaging and ferumoxytol. Three techniques, including precontrast two-dimensional time-of-flight (TOF) imaging, ferumoxytol-enhanced bright-blood imaging, and ferumoxytol-enhanced dark-blood imaging, were applied. Image quality for precontrast and ferumoxytol-enhanced images was analyzed by using a four-point scale. Thrombus was depicted as a filling defect within the blood pool on bright-blood images and as bright tissue that appeared highly contrasted against a dark background on dark-blood images. Image quality of ferumoxytol-enhanced images was uniformly superior to that of precontrast TOF images (P = .007). Compared with precontrast TOF images, ferumoxytol-enhanced bright-blood images had higher contrast-to-noise ratios (CNRs) between thrombus and blood (P = .051), whereas ferumoxytol-enhanced dark-blood images showed significantly higher CNRs between thrombus and surrounding muscle (P = .008). Ferumoxytol-enhanced MR imaging can depict DVT with a dual-contrast mechanism and show the extent of thrombus.

Objective To investigate the feasibility of studying renal effects of nitric oxide synthase inhibition (NOSi) in humans by blood oxygenation level-dependent (BOLD) MRI. Nitric oxide (NO) is known to play a key role in the pathophysiology of hypertension and previous reports suggest reduced bio-availability of NO in the kidneys of hypertensive rats and hence show reduced response to NOSi using BOLD MRI. Ability to perform similar studies in humans could potentially lead to detection of early changes before development of symptoms, and to monitor novel interventions targeted toward improved NO bioavailability. The specific goals for this study were: (1) to examine whether lower doses and dose rate of administration of NOSi such as those previously used in humans can be detected by BOLD MRI in rat kidneys, (2) to compare changes in R2* to direct measures of renal medullary oxygen levels and blood flow using invasive probes (OxyLite/OxyFlo), and (3) to examine for the first time the effect of NOSi on intrarenal oxygenation in humans. Material and Methods In rat kidneys, acute changes in renal tissue oxygenation induced by different doses (2, 4, and 10 mg/kg) of N-nitro-l-arginine methyl ester were studied in 36 Sprague Dawley rats, which were equally divided into BOLD MRI and OxyLite/OxyFlo groups. Similarly in humans, acute changes in renal oxygenation were induced by 2 different NOS inhibitors NG-monomethyl-l-arginine (4.25 mg/kg) in 7 volunteers and N-nitro-l-arginine methyl ester (2 mg/kg and 4 mg/kg) in 6 healthy young volunteers. A multiple gradient echo sequence was used in both rats (TE = 4.4 –57.8 milliseconds with 3.6 milliseconds interecho spacing) and humans (TE = 6.4–40.8 milliseconds with a 2.3 milliseconds interecho spacing) to acquire 16 T2*-weighted images. R2* maps were constructed by fitting a single exponential decay to the image data on pixel by pixel basis. R2* measurements in the cortex and medulla were performed by regions of interest analysis. Measurements were performed before and during infusion of NOSi. Results In rats, NOSi decreased medullary pO2 and blood flow in a dose-dependent manner, and BOLD MRI showed an increase in medullary R2* consistent with the invasive pO2 measurements. In humans, BOLD MRI similarly showed an increase in medullary and cortical R2* after NOSi in a dose-dependent manner. In both rats and humans, the R2* values fell back toward baseline before the end of the infusion period. Conclusion Comparison of BOLD MRI measurements with those using invasive probes suggests that changes in blood flow are at least partly responsible for observed changes with BOLD MRI. Monitoring changes after NOSi by renal BOLD MRI in vivo in human kidneys are feasible, and preliminary findings are consistent with observations in rat kidneys. Future studies are warranted to fully understand the apparent reversal in R2* changes during the infusion of NOSi.