Cerebral atrophy in bulimia.

The extent of cerebral atrophy in 8 consecutively chosen unmedicated bulimics and 8 normal controls was determined by magnetic resonance imaging. There was no history of anorexia nervosa or alcoholism in either group. Measures obtained included the ratio of cerebral to cranial area at the midsagittal section, as well as maximum ventricle/brain ratio in the axial plane. Sagittal cerebral/cranial ratio was significantly less in the bulimic group than in controls [0.82 +/- 0.04 (SD) versus 0.90 +/- 0.03, Z = -2.74, p = 0.006, two-tailed Mann-Whitney U-test], whereas ventricle/brain ratio was not significantly different between groups. Implications for the occurrence of cortical atrophy in normal-weight bulimics, as well as for the relative absence of ventricular enlargement in these patients, are discussed.

Effects of ECT on brain structure: a pilot prospective magnetic resonance imaging study.

The authors describe a pilot prospective investigation of the effects of ECT on brain structure using magnetic resonance imaging (MRI). In nine patients with major depression, a course of ECT produced no acute changes in brain structure according to blind raters' assessments of cortical atrophy and global comparison of pre- and post-ECT studies. There were also no significant changes in the ventricle-brain ratios. Pre-ECT brain abnormalities were common in these patients yet were also unaffected by ECT. Future MRI studies of ECT should include more subjects and should address long-term changes and subtle brain abnormalities.

Detection, characterization and functional assessment of reperfused Q-wave acute myocardial infarction by cine magnetic resonance imaging.

The capability of dynamic gradient-refocused magnetic resonance imaging (cine MRI) to detect, localize and functionally assess acute myocardial infarction (AMI) in 25 patients at a mean time interval of 7 days after AMI was evaluated. Fifteen asymptomatic volunteers were also examined to determine the specificity of the observations. Upon presentation, each patient received intravenous thrombolytic therapy, underwent immediate cardiac catheterization and had percutaneous transluminal coronary angioplasty performed when coronary reperfusion was absent. Twenty-four of the patients had documented coronary reperfusion at a mean interval of 259 +/- 129 minutes. Global ejection fraction and regional wall motion abnormalities were evaluated at 7 days by cine MRI, left ventriculography and radionuclide angiography. Twenty patients with both an absolute decrease in myocardial signal and a matched regional wall motion abnormality had AMI properly identified by cine MRI. In contrast, the finding of both decreased signal intensity and a matched regional wall motion abnormality was absent in the group of asymptomatic volunteers. The ejection fraction by cine MRI correlated better with the ejection fraction by left ventriculography (r = 0.94, standard error of the estimate = 3.6) than did the ejection fraction by radionuclide angiography (r = 0.82, standard error of the estimate = 5.8). The regional wall motion concordance rate in comparison to left ventriculography was similar for both cine MRI (69%) and radionuclide angiography (65%). These findings suggest that cine MRI may play an important role in the future detection and functional characterization of AMI.

Magnetic resonance imaging evaluation of pulmonary vascular malformations.

OBJECTIVE: The purpose of our study was to establish magnetic resonance imaging (MRI) criteria for the diagnosis of pulmonary vascular malformations (PVMs). MATERIALS AND METHODS: Since 1987, 11 patients have been referred for chest MRI at our institution because of findings suggestive of a PVM. They were evaluated with a 1.5-T MRI system, incorporating a combination of spin-echo, gradient-recalled echo (GRE) cine, and 2-D phase contrast (PC) cine sequences. We used the following MRI criteria to diagnose PVM: (1) flow void or intermediate gray signal on spine-echo sequences; (2) bright signal on GRE cine sequences; and (3) bright signal consistent with flow detected on PC cine sequences using relatively low velocity ranges. Twelve patients not suspected of having a PVM served as controls; all had both MRI and pulmonary angiography to evaluate for central pulmonary embolus. RESULTS: Eight patients in the study group had PVM as determined with MRI using these criteria. In four of these patients, a PVM was confirmed by subsequent pulmonary angiography. Three patients did not have PVM utilizing these criteria; two had neoplasms and one had presumed mucus plugging and/or atelectasis that resolved spontaneously. The smallest vascular malformation detected by MRI was 1 cm. None of the control patients had PVM by MRI or pulmonary angiography. CONCLUSION: Utilizing these criteria, we believe that MRI is potentially an excellent noninvasive modality to evaluate PVM, and we stress that some form of PC cine sequence must be performed to determine if indeed there is blood flow within a suspicious lesion.

A cardiac phantom and pulsatile flow pump for magnetic resonance imaging studies.

Fast scan magnetic resonance imaging (MRI) acquisitions are a rapid noninvasive means of evaluating the cardiovascular system. Because the appearance of flowing blood is highly variable, the interpretation of these images is sometimes difficult. A nonferromagnetic phantom that could generate lifelike pulsatile flow and also simulate the motions of the beating heart would facilitate image interpretation. This paper describes an MRI-compatible cardiovascular phantom that mimics the motions of the heart and also creates physiologic pulsatile flow. The phantom consists of a ventricle and an air pump that drives it. The pump is connected to the ventricle with seven meters of air hose so that the pump (which has ferromagnetic parts) can be placed outside the magnet room. The ventricle is placed in an airtight Plexiglas cylinder and the pump alternately pressurizes and depressurizes the cylinder, driving fluid in and out of the ventricle. The motions of the ventricular wall simulate the motions of the heart, and the pulsatile flow generated is of physiologic velocities and volumes. This phantom also can be used with other methods of evaluating cardiovascular function, such as MUGAS, angiography, and Doppler, allowing correlation between MRI and other modalities. Finally, the phantom can be used to study almost any aspect of cardiovascular function from pulsatile flow velocity to ventricular studies (ejection fractions, cardiac output, wall motion) and even studies of stenotic or regurgitant valves.

Optimizing electrocardiograph electrode placement for cardiac-gated magnetic resonance imaging.

Electrocardiographs recorded in a magnetic field for cardiac-gating in magnetic resonance imaging (MRI) are complicated by blood flow-induced potentials. This study examines which lead of the standard 12-lead ECG maximizes the QRS while minimizing flow-induced interference. Twelve-lead ECGs were performed on normal volunteers (n = 9) and patients (n = 13) in and out of the bore of a 1.5 Tesla imaging magnet. The amplitude of the major flow-induced potentials was measured, and the vectors of largest induced potential and the QRS axis were plotted for each subject. ECGs obtained outside and inside the magnet were digitized and subtracted (in magnet ECG--out of magnet ECG = artifact ECG) and the peaks of the resultant curves measured. Superimposed potentials were largest in the early T wave and late S-T segment in leads I, II, V1, and V2, and smallest in III and AVF. A low-amplitude 7-to 10-Hz signal occurred in most leads. In the frontal plane, QRS axes and flow potential vectors were closely clustered. In the transverse plane, QRS axes generally followed leads V5 or V6, whereas the flow potential vectors followed leads V1, V2, or V3. The normal and patient groups did not differ. Although leads III and AVP showed the smallest superimposed potentials, V5, V6, or a left posterior chest lead may maximize QRS and reduce artifact most consistently. A 7- to 10-Hz frequency filter may help eliminate artifacts in some subjects.

Evaluation of flow through simulated vascular stenoses with gradient echo magnetic resonance imaging.

Magnetic resonance imaging using gradient echo sequences can quickly generate dynamic images of the cardiovascular system. We used a gradient echo sequence (repetition time = 21 milliseconds, echo time = 12 milliseconds, flip angle = 30 degrees) to evaluate how a simulated vascular stenoses affects the signal intensity of flowing fluid. Axial slices were obtained at regular intervals along a plastic tube containing a circular constriction (25%, 51%, or 73% reduction of cross-sectional area). Image data collected at each slice level were used to reconstruct 32 images evenly spaced in time over one cycle of pulsatile flow. Contrast ratios were calculated between signal intensities from tube lumen and surrounding stationary water jacket. Upstream from each stenosis, signal intensity increased during systole and decreased during diastole, paralleling the changes in velocity we measured with a flow probe. However, within the 51% and 73% stenoses and just beyond them, there were consistent decreases in systolic signal intensity. Flow through the 25% constriction had little effect on the signal intensity pattern. These results suggest that the gradient echo pulse sequence may be useful in evaluating disturbed flow associated with vascular stenoses.

CT-determined pulmonary artery diameters in predicting pulmonary hypertension.

This study was to determine if the diameters of pulmonary arteries measured from computed tomographic (CT) scans could be used 1) as indicators of pulmonary artery hypertension and 2) as a reliable base for calculating mean pulmonary artery pressure. The diameters of the main, left, proximal right, distal right, interlobar, and left descending pulmonary arteries were measured from CT scans in 32 patients with cardiopulmonary disease and in 26 age- and sex-matched control subjects. Diameters were measured using a special computer program that could display a CT density profile of the artery and its adjacent tissues. The upper limit of normal diameter for the main pulmonary artery was found to be 28.6 mm (mean + 2 SD). In the patient group, the diameters were correlated with data from cardiac catheterization. In these patients, a diameter of the main pulmonary artery above 28.6 mm readily predicted the presence of pulmonary hypertension. The calculated cross-sectional areas of the main and interlobar pulmonary arteries (normalized for body surface area [BAS]) were found to give the best estimates of mean pulmonary artery pressure (r = 0.89, P less than 0.001 and r = 0.66, P less than 0.001). Multiple regression analysis gave the useful equation: mean pulmonary artery pressure = -10.92 + 0.07646 X area of main pulmonary artery/BSA + 0.08084 X area of the right interlobar pulmonary artery/BSA (r = 0.93, P less than 0.0001). Because CT allows precise, noninvasive measurement of the diameter of pulmonary arteries, it can be of value in detecting pulmonary hypertension and estimating mean pulmonary artery pressure.

Measurement of cardiac output by computed transmission tomography.

The capability of computed tomography (CT) scanning to measure cardiac output was explored using ten anesthetized dogs, and the results were compared with those obtained by thermodilution. Dynamic CT scans were performed at the level of the aortic root while small peripheral intravenous boluses of contrast medium were injected. Time/density curves were generated using a gamma variate fitting program. These were used to estimate cardiac output by applying indicator dilution principles. CT results correlated favorably (r = 0.86) with those of thermodilution. This feasibility study indicates the utility of CT for obtaining physiologic measurements of cardiac function and should encourage further studies to develop the potential of CT for cardiovascular diagnostic purposes.

Chemical shift imaging of atherosclerosis at 7.0 Tesla.

Chemical shift imaging (CSI) was performed on cadaveric atherosclerotic fibrous plaques, periaortic adipose tissue, and cholesterol standards using a 7.0 Tesla horizontal bore prototype imaging spectrometer. Proton spectroscopy of intact tissue and deuterated chloroform extracted samples was done at the equivalent field strength of 7.0 Tesla on a vertical bore spectrometer, including studies of temperature dependence and T2 relaxation measurements. Spectra obtained using CSI on the imaging magnet were comparable with those from the conventional vertical spectrometer. Fibrous plaques and adipose tissue had unique spectral features, differing in the ratios of their water and various fat components. Chloroform extractions revealed a typical cholesteric ester spectrum for the fibrous plaque in contrast to the triglyceride spectrum of the adipose tissue. These two tissues also had different T2 relaxation measurements of their major fat resonances, with fibrous plaques having a short T2 compared to adipose tissue (15.9 milliseconds vs. 46.2 milliseconds). Temperature dependence studies showed that spectral signal intensity of the fat resonance of the fibrous plaque increased while linewidth decreased with increasing temperature from 24 degrees C to 37 degrees C. Atherosclerotic lesions may be studied at 7.0 Tesla, and NMR parameters defined in the present study may be used for further studies at other magnetic field strengths.

Effects of turbulence on signal intensity in gradient echo images.

Although the appearance of laminar vascular flow in magnetic resonance (MR) images has been characterized, there is no general agreement about the effect of turbulent flow on MR signal intensity. This study uses a fast scan gradient echo pulse sequence to evaluate nonpulsatile turbulent flow in two different models. The first model simulated flow in normal vascular structure. It generated nonpulsatile, laminar and turbulent flow in straight, smooth-walled Plexiglas tubes. The second model simulated flow through a vascular stenosis. It generated nonpulsatile, laminar, and turbulent flow through an orifice. Velocities and flow rates ranged from low physiologic to well above the physiologic range (velocity = .3 to 280 cm/second, flow rate from .15 to 40 L/minute). Transition from laminar to turbulent flow was observed with dye streams. Turbulent flow in straight, smooth-walled vessels was not associated with a decrease in MR signal intensity even at the highest velocities and flow rates studied. The transition from laminar to turbulent flow through an orifice is not associated with a decrease in gradient echo signal intensity. As the intensity of the turbulent flow increases, however, there is a threshold above which signal intensity decreases linearly as turbulence increases (r = .97). This study suggests that flow in normal vascular structures should not be associated with decreased signal intensity in gradient echo images. Turbulent flow through areas such as valves, valvular lesions or vascular stenoses, may be associated with a decrease in gradient echo signal intensity.

Work in progress: in vitro analysis of pleural fluid analogs by proton magnetic resonance. Preliminary studies at 1.5T.

To test the potential of 1.5 Tesla magnetic resonance imaging (MRI) for assessing the protein concentration of pleural effusions, five pleural fluid analogs (saline + 0, 2, 4, 6, 8 g albumin/100 mL) and, for comparison, four saline dilutions of whole blood were evaluated in vitro. The relaxation rates (1/T1, 1/T2) of albumin solutions were determined by 1.5 T spectroscopy (MRS) and correlated with albumin concentration (1/T1:slope 0.02, r + 0.89, P less than .05; 1/T2: slope 0.16, r = 0.997, P less than .001). MRI studies of these solutions showed no significant correlation with 1/T1, but 1/T2 showed a positive correlation with albumin concentration (r = 0.98, P less than .01). Both MRI relaxation rates were significantly correlated with blood concentration, and slopes were greater than for albumin solutions. These preliminary studies, demonstrating differences in correlation between relaxation rates and the concentration of albumin and blood, suggest that MRI has the potential for differentiating pleural effusions of different chemical composition.

Evaluation of acute renal failure with magnetic resonance imaging using gradient-echo and Gd-DTPA.

Detection of acute renal failure (ARF) using fast-scan magnetic resonance imaging (MRI) with Gd-DTPA was studied in a dog model. ARF was produced in five dogs by infusion of norepinephrine (0.75 micrograms/kg/min) into the renal arteries for 40 minutes. MRI was performed 1 hour later and compared with baseline (pre-ARF) MRI. There was no significant difference in the ratios of signal intensity-vs.-time curves from 0 to 35 seconds after injection of Gd-DTPA. However, a difference between the outer and inner medulla was significant in the time period of 5 to 20 minutes after Gd-DTPA injection. These later signal intensity differences by fast-scan (gradient-echo) technique may be useful in the evaluation of ARF.

Single breath-hold pulmonary magnetic resonance angiography. Optimization and comparison of three imaging strategies.

RATIONALE AND OBJECTIVES: Ultrafast gradient-recalled-echo techniques for obtaining high-quality pulmonary magnetic resonance angiograms within a single breath-hold were optimized. METHODS: Fourteen subjects were imaged with both the body coil and a phased-array surface coil, using three gradient-recalled-echo pulse sequences: 1) two-dimensional sequential; 2) two-dimensional interleaved; and 3) volumetric acquisitions. Image quality was assessed with varied flip angle, receiver bandwidth, slice thickness/number, and matrix size. Cardiac compensation diminished ghost artifacts in the interleaved sequence. Individual sagittal sections and maximum intensity projections were reviewed. RESULTS: Pulmonary magnetic resonance angiograms acquired with volumetric and two-dimensional interleaved gradient-recalled-echo pulse sequences benefit greatest from intravenous gadolinium and result in greater pulmonary arterial visualization than traditional time-of-flight techniques. Phased-array coils result in improved vessel detection. CONCLUSIONS: High-quality breath-held pulmonary magnetic resonance angiography can be obtained with an intravenous contrast-enhanced gradient-recalled-echo acquisition; however, image quality is dependent on the pulse sequence.

Evaluation of myocardial motion tracking with cine-phase contrast magnetic resonance imaging.

RATIONALE AND OBJECTIVES: The accuracy of myocardial motion measurements, computed from cine-phase contrast (cine-PC) magnetic resonance (MR) velocity data, was compared with directly visualized motion of MR signal voids caused by implanted tantalum markers in anesthetized dogs. METHODS: Magnetic resonance imaging (MRI) data were electrocardiogram-gated and divided into 16 phases per cardiac cycle. Myocardial trajectories as a function of time in the cardiac cycle were measured using both methods for four to seven markers in each of eight animals. RESULTS: The peak observed in-plane excursion was 4.0 +/- 2.1 mm. The average deviation between displacements derived from velocity data versus displacements visualized directly was 1.1 +/- 0.7 mm (27.5% of the peak displacement). The difference was less if three separate MR scans were used to measure each velocity component in the cine-PC method. This improvement is probably caused by improved temporal resolution. CONCLUSIONS: Cine-PC MRI offers a noninvasive method for accurate quantification of myocardial motion.

Effect of magnetic resonance imaging on Xenopus laevis embryogenesis.

Xenopus laevis embryos, exposed to various lengths of magnetic resonance imaging (MRI), demonstrated no abnormal morphology, function, or developmental delays. The overall protein profiles and nucleic acid ratios were similar compared to controls. Results suggest there are no adverse effects of MRI components on the development of this vertebrate.

Vascular morphology by three-dimensional magnetic resonance imaging.

A three-dimensional examination of blood vessels is provided using MR data from seven cases. The vascular surfaces are constructed with an algorithm that automatically follows the selected artery or vein and generates a projected three-dimensional gradient shaded image. Fast 3DFT pulse sequences were optimized to enhance the time-of-flight contrast of the intravascular region. By increasing the surface threshold value in a three-dimensional head study, the flesh of a patient's face was peeled away to demonstrate the superfacial temporal artery. Gated cardiac images show the great vessels and cardiac chambers. A three-dimensional view of the aorta shows an irregular surface in the vicinity of an adrenal tumor. 3D MR exams provide a non-invasive technique for assessing vascular morphology in a clinical setting.

Evaluation of steady and pulsatile flow with dynamic MRI using limited flip angles and gradient refocused echoes.

Magnetic resonance imaging sequences utilizing limited flip angles and gradient echoes yield rapid (less than 2 min) dynamic images of the cardiovascular system. These images contain both accurate anatomical and functional information. Using a gradient refocused acquisition in the steady state (GRASS) in the CINE mode, we studied the relationship between gradient echo signal intensity and velocity of steady and pulsatile flow in a phantom simulating medium to large vessels. Images were acquired on a 1.5 Tesla system (repetition time = 21 ms, echo time = 12 ms, flip angle = 30 degrees). Data from each pulse interval were sorted in 16 images. Signal intensities from flow tube lumina and surrounding stationary water jacket were used to calculate contrast ratios which were compared to velocity measurements made with electromagnetic (EM) flow probes outside the magnet room. During steady flow, signal intensity contrast ratios increased with increasing flow and in a 10 mm thick slice, reached a peak at 48 cm/s, and declined for velocities up to 90 cm/s. Changes in instantaneous velocity during pulsatile flow correlated well (r greater than .88) with signal intensity changes up to a maximum mean velocity of 17 cm/s. Total signal intensity from the lumen for an "R to R" interval correlated extremely well (r greater than .97) with mean pulsatile flow velocities up to 30 cm/s. The excellent correlation between gradient echo signal intensity and actual flow velocities suggests that this imaging sequence might be useful for evaluating normal and pathologic flow phenomena.

Rapid calculation of T1 using variable flip angle gradient refocused imaging.

We present a method for rapid measurement of T1 relaxation times using gradient refocused images at limited flip angles and short repetition times. This "variable nutation" techniques was investigated using a T1 phantom. There was a high correlation between measurements obtained with the variable nutation and partial saturation techniques. The ability of this method to create calculated T1 images is also demonstrated. We conclude that the variable nutation method may allow measurement of T1 relaxation times with a significant reduction in acquisition time compared to partial saturation techniques.

Heterogeneous signal intensity in magnetic resonance images of hypertrophied left ventricular myocardium.

Left ventricular hypertrophy is associated with decreased longevity and often leads to congestive heart failure. An exploratory study of magnetic resonance imaging in human left ventricular hypertrophy was performed. First, 13 patients with left ventricular hypertrophy and 7 controls of similar ages were studied using electrocardiogramgated end-diastolic images. Visual inspection suggested that low-intensity zones were frequently found within the hypertrophied myocardium. To verify this observation, the images were processed with semi-automatic edge detection and a derivative-based tissue characterization algorithm, yielding tissue heterogeneity indices (THI-A and THI-V) which objectively measured the low-intensity zones. THI-A and THI-V were both significantly greater in left ventricular hypertrophy patients than in controls (THI-A: 0.111 vs 0.038, p = 0.009). THI was also significantly correlated with duration of disease and electrocardiographic abnormalities. To validate these initial findings prospectively, the same quantitative analysis was applied to magnetic resonance images of an additional 20 left ventricular hypertrophy patients and 12 controls from two institutions, using different imaging systems and different acquisition parameters. Again, THI was significantly greater in patients than in controls. Analysis of end-systolic images yielded similar results. In four dogs with left ventricular hypertrophy induced by aortic banding, THI showed a statistically significant increase as left ventricular hypertrophy developed. Hypertrophied myocardium thus shows reproducible differences from normal tissue with magnetic resonance imaging; hence, quantitative magnetic resonance tissue characterization may be useful in assessing pathologic changes in LVH.