Mark A. Griswold

Oxygen enhanced MR ventilation imaging of the lung

OBJECTIVE The purpose of this study was to show the feasibility of oxygen-enhanced MR ventilation imaging in a clinical setting with correlation to standard pulmonary function tests, high-resolution CT, and (81m)Kr ventilation scintigraphy. SUBJECTS AND METHODS Seven healthy volunteers, 10 lung cancer patients, and eight lung cancer patients with pulmonary emphysema were studied. A respiratory synchronized inversion-recovery single-shot turbo-spin-echo sequence (TE, 16; inversion time, 720 msec; interecho spacing, 4 msec) was used for data acquisition. The following paradigm of oxygen inhalation was used: 21% oxygen (room air), 100% oxygen, 21% oxygen. MR imaging data including maximum mean relative enhancement ratio and mean slope of relative enhancement were correlated with forced expiratory volume in 1 sec, diffusing lung capacity, high-resolution CT emphysema score, and mean distribution ratio of (81m)Kr ventilation scintigraphy. RESULTS Oxygen-enhanced MR ventilation images were obtained in all subjects. Maximum mean relative enhancement ratio and mean slope of relative enhancement of lung cancer patients were significantly decreased compared with those of the healthy volunteers (p < 0.0001, p < 0.0001). The mean slope of relative enhancement in lung cancer patients with pulmonary emphysema was significantly lower than that of lung cancer patients without pulmonary emphysema (p < 0.0001). Maximum mean relative enhancement ratio (r(2) = 0.81) was excellently correlated with diffusing lung capacity. Mean slope of relative enhancement (r(2) = 0.74) was strongly correlated with forced expiratory volume in 1 sec. Maximum mean relative enhancement had good correlation with the high-resolution CT emphysema score (r(2) = 0.38). The maximum mean relative enhancement had a strong correlation with the distribution ratio (r(2) = 0.77). CONCLUSION Oxygen-enhanced MR ventilation imaging in human subjects showed regional changes in ventilation, thus reflecting regional lung function.

Silent functional magnetic resonance imaging demonstrates focal activation in rapid eye movement sleep

Article abstract Functional imaging of human sleep has been performed with nuclear medicine methods, but MRI has been difficult to implement, in part because of the noise associated with echo-planar imaging as well as the difficulty in reading physiologic signals in the MRI environment. We describe a silent MR sequence that can record brain activation over many hours with simultaneous acquisition of an EEG. This shows activation of occipital cortex and deactivation of frontal cortex during REM sleep, in agreement with previous studies using other techniques.

SMASH imaging with an eight element multiplexed RF coil array

SMASH (SiMultaneous Acquisition of Spatial Harmonics) is a technique which can be used to acquire multiple lines ofk-space in parallel, by using spatial information from a radiofrequency coil array to perform some of the encoding normally produced by gradients. Using SMASH, imaging speed can be increased up to a maximum acceleration factor equal to the number of coil array elements. This work is a feasibility study which examines the use of SMASH with specialized coil array and data reception hardware to achieve previously unattainable accelerations. An eight element linear SMASH array was designed to operate in conjunction with a time domain multiplexing system to examine the effectiveness of SMASH imaging with as much as eightfold acceleration factors. Time domain multiplexing allowed the multiple independent array elements to be sampled through a standard single-channel receiver. SMASH-reconstructed images using this system were compared with reference images, and signal to noise ratio and reconstruction artifact power were measured as a function of acceleration factor. Results of the imaging experiments showed an almost constant SNR for SMASH acceleration factors of up to eight. Artifact power remained low within this range of acceleration factors. This study demonstrates that efficient SMASH imaging at high acceleration factors is feasible using appropriate hardware, and that time domain multiplexing is a convenient strategy to provide the multiple channels required for rapid imaging with large arrays.

Simultaneous T1 and T2 Brain Relaxometry in Asymptomatic Volunteers using Magnetic Resonance Fingerprinting.

Magnetic resonance fingerprinting (MRF) is an imaging tool that produces multiple magnetic resonance imaging parametric maps from a single scan. Herein we describe the normal range and progression of MRF-derived relaxometry values with age in healthy individuals. In total, 56 normal volunteers (24 men and 32 women) aged 11-71 years were scanned. Regions of interest were drawn on T1 and T2 maps in 38 areas, including lobar and deep white matter (WM), deep gray nuclei, thalami, and posterior fossa structures. Relaxometry differences were assessed using a forward stepwise selection of a baseline model that included either sex, age, or both, where variables were included if they contributed significantly (P < .05). In addition, differences in regional anatomy, including comparisons between hemispheres and between anatomical subcomponents, were assessed by paired t tests. MRF-derived T1 and T2 in frontal WM regions increased with age, whereas occipital and temporal regions remained relatively stable. Deep gray nuclei such as substantia nigra, were found to have age-related decreases in relaxometry. Differences in sex were observed in T1 and T2 of temporal regions, the cerebellum, and pons. Men were found to have more rapid age-related changes in frontal and parietal WM. Regional differences were identified between hemispheres, between the genu and splenium of the corpus callosum, and between posteromedial and anterolateral thalami. In conclusion, MRF quantification measures relaxometry trends in healthy individuals that are in agreement with the current understanding of neurobiology and has the ability to uncover additional patterns that have not yet been explored.