Jason A. Polzin

Evaluation of the Reproducibility of Intrarenal and Measurements Following Administration of Furosemide and During Waterload

To estimate the reproducibility of BOLD MRI measurements in the evaluation of intrarenal oxygenation levels.

Myocardial delayed enhancement imaging using inversion recovery single-shot steady-state free precession: Initial experience†

To evaluate the feasibility of using an inversion recovery single‐shot steady‐state free precession (SS_SSFP) sequence for myocardial delayed enhancement (MDE) imaging, and to compare SS_SSFP with the conventional inversion recovery segmented fast gradient echo (IR_FGRE) technique.

Helical MR: continuously moving table axial imaging with radial acquisitions.

A technique for extended field of view MRI is presented. Similar to helical computed tomography, the method utilizes a continuously moving patient table, a 2D axial slice that remains fixed relative to the MRI magnet, and a radial k‐space trajectory. A fully refocused SSFP acquisition enables spatial resolution comparable to current clinical protocols in scan times that are sufficiently short to allow a reasonable breathhold duration. RF transmission and signal reception are performed using the RF body coil and the images are reconstructed in real time. Experimental results are presented that illustrate the techniques ability to resolve small structures in the table‐motion direction. Simulation experiments to study the steady‐state response of the fully refocused SSFP acquisition during continuous table motion are also presented. Finally, whole body images of healthy volunteers demonstrate the high image quality achieved using the helical MRI approach. Magn Reson Med 50:1053–1060, 2003.

Measurement of Coronary Blood Flow and Flow Reserve Using Magnetic Resonance Imaging

PURPOSE It was the purpose of this study to demonstrate the feasibility of performing coronary artery flow and coronary flow reserve (CFR) measurements in normal human volunteers using a magnetic resonance (MR) phase contrast technique. MATERIALS AND METHODS Coronary flow rate, flow velocity, peak flow and CFR were determined at rest and during pharmacologically induced hyperemia in 10 healthy volunteers. The flow measurements were obtained during a single breath-hold by using a fast, prospectively gated, segmented k-space gradient-echo phase contrast acquisition with view sharing (FASTCARD PC) that was modified to improve sampling of the diastolic flow. Data were processed using the standard phase difference (PD) processing techniques as well as a new complex difference (CD) flow measurement method intended to improve the accuracy of flow measurements in small vessels. RESULTS Mean hyperemic flow velocity (40 +/- 16 cm/s) and blood flow (3.9 +/- 1.5 ml/s) rates differed significantly from resting velocity (13 +/- 6.6 cm/s) and flow (1.1 +/- 0.4 ml/s) measurements (p < 0.0001). PD methods consistently measured larger flow rates at rest (24% larger, p < 0.0005) and stress (29% larger, p < 0.0001). CFR, calculated as the ratio of the mean PD flows (4.7 +/- 2.8), was higher than CFR calculated as the ratio of mean CD flows (4.2 +/- 1.8); however, the differences did not reach statistical significance (p = 0.07). Flow measurements performed in adjacent slices of the same vessel correlated well (r = 0.88). CONCLUSIONS Coronary flow and CFR measurements using the MR techniques are feasible and are similar to those reported in the literature for healthy volunteers.

Computing oxygen-enhanced ventilation maps using correlation analysis

Correlation maps of oxygen‐enhanced ventilation were obtained in nine healthy volunteers using complete and selected image series. The complete series included all images acquired with the subjects alternately inhaling room air and 100% oxygen. The selected series were the subsets of the complete series and included only co‐registered images that showed matched diaphragmatic position at maximal expiration. Cross‐correlation was computed between the time response function of each pixel and the input function representing the alternation between periods of room air and 100% oxygen inhalation. The confidence level for the correlation analysis was set to 0.01. Pulmonary parenchymal anatomy was consistently reproduced throughout the lung, even in anterior slices where published data have reported correlation problems. The overall average correlation coefficient was 0.66 ± 0.07 for the complete series and 0.75 ± 0.08 for the selected series. It was concluded that correlation analysis could be used to reconstruct qualitative oxygen‐enhanced ventilation maps. Magn Reson Med 49:591–594, 2003.

Floating table isotropic projection (FLIPR) acquisition: A time-resolved 3D method for extended field-of-view MRI during continuous table motion

In this work, 3D vastly undersampled isotropic projection (VIPR) acquisition is used simultaneously with continuous table motion to extend the superior/inferior (S/I) FOV for MR angiograms. The new technique is termed floating table isotropic PR (FLIPR). The use of 3D PR in conjunction with table motion obviates the need to locate and prescribe imaging volumes containing the major blood vessels over the large superior–inferior (S/I) ranges encountered in whole‐body imaging. In addition, the FLIPR technique provides extended anterior–posterior (A/P) abdominal coverage, isotropic spatial resolution, and temporal resolution. In volunteer studies, FLIPR MR angiograms with 1.6‐mm isotropic spatial resolution that approached whole body in extent were acquired in less than 2 min. Magn Reson Med 52:1093–1102, 2004.

Detection of acute renal ischemia in swine using blood oxygen level-dependent magnetic resonance imaging.

To determine the feasibility and sensitivity of blood oxygen level‐dependent (BOLD) magnetic resonance imaging (MRI) to detect acute renal ischemia, using a swine model, and to present the causes of variability and assess techniques that minimize variability introduced during data analysis.

Influence of oxygen flow rate on signal and T1 changes in oxygen-enhanced ventilation imaging

To investigate the optimal oxygen flow rate for oxygen‐enhanced MR ventilation imaging.

Correction for gradient nonlinearity in continuously moving table MR imaging

Recently, a number of methods have been demonstrated for large field of view MR imaging using continuous table motion. As with conventional, fixed‐table MRI, the spatial encoding is performed using magnetic field gradients. However, it is demonstrated in this work that as a consequence of every measurement being made at a slightly different displacement between the object and the gradient field, gradient nonlinearities are manifest as blurring in addition to spatial distortion. Moreover, the blurring is spatially dependent. It is also shown that correcting all phase‐encoding steps individually or in groups can reduce these effects. Phantom and in vivo results are shown which demonstrate the effectiveness of the correction. Magn Reson Med 52:181–187, 2004.

Ventilation‐perfusion ratio of signal intensity in human lung using oxygen‐enhanced and arterial spin labeling techniques

This study investigates the distribution of ventilation‐perfusion (V/Q) signal intensity (SI) ratios using oxygen‐enhanced and arterial spin labeling (ASL) techniques in the lungs of 10 healthy volunteers. Ventilation and perfusion images were simultaneously acquired using the flow‐sensitive alternating inversion recovery (FAIR) method as volunteers alternately inhaled room air and 100% oxygen. Images of the T1 distribution were calculated for five volunteers for both selective (T1f) and nonselective (T1) inversion. The average T1 was 1360 ms ± 116 ms, and the average T1f was 1012 ms ± 112 ms, yielding a difference that is statistically significant (P < 0.002). Excluding large pulmonary vessels, the average V/Q SI ratios were 0.355 ± 0.073 for the left lung and 0.371 ± 0.093 for the right lung, which are in agreement with the theoretical V/Q SI ratio. Plots of the V/Q SI ratio are similar to the logarithmic normal distribution obtained by multiple inert gas elimination techniques, with a range of ratios matching ventilation and perfusion. This MRI V/Q technique is completely noninvasive and does not involve ionized radiation. A limitation of this method is the nonsimultaneous acquisition of perfusion and ventilation data, with oxygen administered only for the ventilation data. Magn Reson Med 48:341–350, 2002.