Jack Knight-Scott

Hyperpolarized 3He MR lung ventilation imaging in asthmatics: Preliminary findings

Asthma is a disease characterized by chronic inflammation and reversible obstruction of the small airways resulting in impaired pulmonary ventilation. Hyperpolarized 3He magnetic resonance (MR) lung imaging is a new technology that provides a detailed image of lung ventilation. Hyperpolarized 3He lung imaging was performed in 10 asthmatics and 10 healthy subjects. Seven asthmatics had ventilation defects distributed throughout the lungs compared with none of the normal subjects. These ventilation defects were more numerous and larger in the two symptomatic asthmatics who had abnormal spirometry. Ventilation defects studied over time demonstrated no change in appearance over 30–60 minutes. One asthmatic subject was studied twice in a three‐week period and had ventilation defects which resolved and appeared in that time. This same subject was studied before and after bronchodilator therapy, and all ventilation defects resolved after therapy. Hyperpolarized 3He lung imaging can detect the small, reversible ventilation defects that characterize asthma. The ability to visualize lung ventilation offers a direct method of assessing asthmatics and their response to therapy. J. Magn. Reson. Imaging 2001;13:378–384.

Improved visualization of the human lung in 1H MRI using multiple inversion recovery for simultaneous suppression of signal contributions from fat and muscle

1H magnetic resonance imaging of the lung is hampered by the low contrast between lung parenchyma, and muscle and fat in the thorax. We show that it is possible to improve contrast greatly and thereby enhance the visibility of the lung, by suppression of signal of surrounding muscle and fat based on differences in T1 relaxation times using a double inversion recovery preparation pulses (TI1 800 msec, and TI2 150 msec) and a half‐Fourier acquisition single‐shot turbo spin‐echo (HASTE) sequence. The measured T1 values for the right and left lungs at 1.5 T were 1.37 ± 0.18 and 1.41 ± 0.21 sec, respectively. Magn Reson Med 41:866–870, 1999.

Very short echo time improves the precision of glutamate detection at 3T in 1H magnetic resonance spectroscopy.

To examine the precision of glutamate detection using a very short echo time (TE) phase rotation STEAM (PR‐STEAM) sequence.

Molality as a unit of measure for expressing 1H MRS brain metabolite concentrations in vivo

Absolute concentrations of cerebral metabolite in in vivo 1H magnetic resonance spectroscopy studies (1H-MRS) are widely reported in molar units as moles per liter of tissue, or in molal units as moles per kilogram of tissue. Such measurements require external referencing or assumptions as to local water content. To reduce the scan time, avoid assumptions that may be invalid under specific pathologies, and provide a universally accessible referencing procedure, we suggest that metabolite concentrations from 1H-MRS measurements in vivo be reported in molal units as moles per kilogram of tissue water. Using internal water referencing, a two-compartment water model, a simulated brain spectrum for peak identification, and a spectroscopic bi-exponential spin-spin relaxation segmentation technique, we measured the absolute concentrations for the four common 1H brain metabolites: choline (Cho), myo-inositol (mIno), phosphocreatine + creatine (Cr), and N-acetyl-aspartate (NAA), in the hippocampal region (n = 26) and along the Sylvian fissure (n = 61) of 35 healthy adults. A stimulated echo localization method (20 ms echo time, 10 ms mixing time, 4 s repetition time) yielded metabolite concentrations, uncorrected for metabolite relaxation or contributions from macromolecule resonances, that were expectantly higher than with molar literature values. Along the Sylvian fissure the average concentrations (coefficient of variation (CV)) in mmoles/kg of tissue water were 17.6 (12%) for NAA, 14.2 (9%) for Cr, 3.6 (13%) for Cho, and 13.2 (15%) for mIno. Respective values for the hippocampal region were 15.7 (20%), 14.7 (16%), 4.6 (19%), and 17.7 (26%). The concentrations of the two regions were significantly different (p </= 0.001) for NAA, mIno, and Cho, a trend in agreement with previous studies. All gray matter Sylvian fissure CV values, except for NAA, were also in agreement with previous 1H-MRS gray matter studies. The reduced precision of the NAA concentration was attributed to overlapping signal contributions from glutamate and glutamine (Glx), suggesting that a detailed Glx model is critical for accurate quantitation of the NAA 2.02 ppm resonance. The reduced precision of the measurements in the hippocampal region was attributed to poor spectral resolution.

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.

q-Space analysis of lung morphometry in vivo with hyperpolarized 3He spectroscopy.

To examine the utility of a 3He spectroscopic q‐space technique for detecting changes in lung morphometry in vivo.

Temporal dynamics of blood flow effects in half-Fourier fast spin echo 1H magnetic resonance imaging of the human lungs

A cardiac‐triggered half‐Fourier single‐shot turbo spin echo (HASTE) technique is currently the method of choice for MR imaging of the lung parenchyma without the use of exogenous contrast agents. In this study, we specifically examined the effects of the cardiac cycle on the HASTE signal intensity of the lungs. Images were obtained from six healthy human volunteers at an end expiration breath‐hold using a HASTE sequence and a variable cardiac‐triggered delay time. Analysis of the data sets showed a 30% decrease in the lung signal intensity during systole, and a 15% decrease during mid‐diastole. These decreases correlate with phases of the cardiac cycle when the blood flow in the lungs is expected to be greatest. Misregistration artifacts, particularly from the pulmonary arteries and aorta, are worse during these periods of signal decrease. To minimize cardiac dependent signal losses, HASTE lung imaging should be performed after systole but before rapid filling of the ventricles.J. Magn. Reson. Imaging 2001;14:411–418.

1H magnetic resonance imaging of human lung using inversion recovery turbo spin echo

Evaluation of lung pathologies using magnetic resonance imaging remains limited, primarily due to the lungs low proton density and high density of magnetic field susceptibility gradients. It is hypothesized that visualization of the lung is possible if signal intensity from muscle and/or fat is suppressed or reduced. Using the inversion recovery and frequency selective saturation pulse with a half‐Fourier single‐shot turbo spin‐echo (HASTE) or a segmented, centric reordered turbo spin‐echo (TSE) readout, signal intensity and contrast of tissues can be manipulated to enhance the visibility of the lung. Multislice images of the lung from 10 healthy volunteers were acquired with negligible motion artifacts. Peripheral pulmonary vessels appear well delineated. T1 maps of the lung are also presented; the overall average was 1335 ± 85 msec and 1245 ± 93 msec with the volunteers performing breath‐holding on end‐expiration and end‐inspiration, respectively. This difference is statistically significant, at P < 0.01. J. Magn. Reson. Imaging 2000;11:616–621.

Effect of lung inflation on arterial spin labeling signal in MR perfusion imaging of human lung.

The effect of lung inflation on arterial spin‐labeling signal in lung perfusion is investigated. Arterial spin‐labeling schemes, called alternation of selective inversion pulse (ASI) and its hybrid (HASI), which uses blood water as an endogenous, freely diffusible tracer, were applied to magnetic resonance (MR) perfusion imaging of the lung. Perfusion‐weighted images of the lung from nine healthy volunteers were obtained at different time delays. There was a significant signal difference in ASI images acquired at different respiratory phases. Greater signal enhancement has been observed when the volunteers performed breath holding on end expiration than on end inspiration. This is in agreement with the normal physiologic effect of lung inflation on the pressure‐flow relationship of pulmonary vasculature. ASI and HASI perfusion‐weighted images show similar lung features and image quality. Preliminary results from pulmonary embolism patients indicate that arterial spin labeling is sensitive for the detection of areas of perfusion deficit. J. Magn. Reson. Imaging 2001;13:954–959.

Gravity-dependent perfusion of the lung demonstrated with the FAIRER arterial spin tagging method

Magnetic resonance imaging of lung perfusion using an arterial spin tagging (AST) sequence called flow sensitive alternating inversion recovery with an extra RF pulse (FAIRER) was performed in the left and right lateral positions in five volunteers. Coronal slices were obtained and the average intensity of each lung was measured. In both positions, an increase in the intensity of the dependent lung was found (229% for left lateral, 40% for right lateral). No change was seen along an isogravitational plane. Lung volumes were measured in each position to account for the compression of the lungs by the heart. This effect was found to be symmetric and did not contribute to the perfusion gradient. This demonstrates that AST is sensitive to gravity-dependent perfusion gradients in the lung.