Reuben S. Mezrich

Magnetic resonance imaging of acute occlusive intestinal ischemia

The mortality of acute superior mesenteric artery occlusion and mesenteric infarction remains high, in part because of the failure to identify the patients with the disorder. A reliable noninvasive diagnostic study may facilitate earlier definitive diagnosis and therapy. Proton magnetic resonance imaging may offer a noninvasive diagnostic alternative. We examined this possibility by using an experimental rabbit model of acute superior mesenteric artery occlusion in this study. Animals were scanned 1 hour after the ischemic insult. Relative intestinal wall signal intensity was increased in experimental (ischemic) animals when compared to sham operated controls on T2-weighted (4.35 +/- 0.5 vs 2.57 +/- 0.31, p less than 0.02) and proton spin density-weighted images (2.1 +/- 0.2 vs 1.4 +/- 0.21, p less than 0.05). Significant increases in image intensity were found on T2-weighted and proton spin density images when compared to control animals. Differences between groups could be further highlighted after the administration of a paramagnetic contrast agent gadolinium diethyltriamine pentacetic acid on T1-weighted images. The data from this preliminary study demonstrate that proton magnetic resonance imaging may be used to discriminate between ischemic and nonischemic small intestine. This noninvasive tool may someday become clinically useful to enhance our diagnostic capabilities when a diagnosis of acute superior mesenteric artery occlusion is being entertained.

Abnormal Cerebral Ventricular Change in Alzheimer's Disease Recorded with Cardiac Gated MRI: A Preliminary Report

We compare high-resolution cardiac gated brain magnetic resonance imaging of 19 young healthy subjects with a small group of demented subjects - mainly probable senile dementia of the Alzheimer type (

Variation of lateral ventricular volume during the cardiac cycle observed by MR imaging.

CSF pulsation suggests variation in the size of the cerebral ventricles during the cardiac cycle. The arterial blood flow and venous outflow are two major components that contribute to the variation. High-resolution MR imaging with cardiac gating provides sharp delineation of the cerebral ventricles with clear boundaries. Subtle changes in the size of the ventricles during the cardiac cycle are measurable with high precision and accuracy by using a sophisticated automated edge-detection algorithm. In 12 normal individuals, the cerebral ventricles were examined, and the size of the lateral ventricles showed a 10-20% change during the cardiac cycle. The pattern is complex but similar in appearance to the intracranial pressure pulse waveform. The variation suggests that the choroid plexus may play a greater role as a source of CSF pulsation that currently acknowledged. The ability to measure the variations in ventricular volume has clinical implication as a noninvasive method for the diagnosis of diseases with abnormal brain elasticity.

In-vitro assessment of the behavior of magnetic resonance angiography in the presence of constrictions.

Sebok NK, Sebok DA, Wilkerson D, Mezrich RS, Zatina M. In-vitro assessment of the behavior of magnetic resonance angiography in the presence of constrictions. Invest Radiol 1993; 28:604-610. RATIONALE AND OBJECTIVES.Timc-of-flight magnetic resonance angiography (TOF/MRA) is increasingly used to assess the nature and severity of stenotic blood vessels. Flow artifacts associated with high flows and/or narrow constrictions may confuse the interpretation of these studies. Accurate TOF/MRA evaluations demand an understanding of the nature of these flow effects. METHODS.A two-dimensional TOF pulse sequence was used to acquire images of five smoothly constricted phantoms at various flows. Analysis included, assessment of phantom appearance and quantification of apparent constriction diameter and signal variations. RESULTS.Most notable flow phenomena were a cone-shaped region of high signal, a region of signal void, and signal preservation along the wall. When visible, constriction diameter was accurately measured. CONCLUSIONS.The behavior observed in TOF/MRA images can be understood by considering the contributing mechanisms of phase dispersion, turbulence, poststenotic flow eddies, flow reversal, and flow separation.

Interleaved magnetic resonance and ultrasound by electronic synchronization.

Increasing attention has been directed toward using magnetic resonance imaging (MRI) to assess blood flow velocity. Complete acceptance of this application requires validation of MRI-derived flow measurements against an accepted flow measurement technique such as Doppler ultrasound in an in vivo situation. To provide an accurate correlation in the presence of rapid changes in blood flow, the MR acquisition should be made nearly simultaneously with the ultrasonic measurements. Unfortunately, standard ultrasound equipment generates radio frequency signal which interferes with MRI. Near-simultaneous acquisition of MR data and ultrasonic blood flow data should be possible if the two measurements are properly synchronized. In the technique presented, ultrasound is made to peacefully coexist with MRI by gating the ultrasound so that it is disabled during the time of MR data acquisition. Phantom and animal experiments confirm the use of this procedure. Although we did not specifically test new fast-scan MR techniques, our technique is completely general and should work equally well with spin-echo as well as newer fast scanning MRI techniques.

The Use of Magnetic Resonance Imaging in the Study of Endema

A method of studying edema using magnetic resonance imaging (MRI) is presented. Three patients with lower extremity edema due to congestive heart failure were imaged with a 0.6 tesla system before and after diuresis. Edge detection algorithms were utilized to precisely outline regions of interest for quantification. Water and nonwater elements were separated within the region of interest to quantify water content. The results show that: (1) Edema can be quantified by use of MRI. (2) Subcutaneous edema is distributed along defined planes (ie, nonuniformly). (3) Increased water content is present not only in the subcutaneous tissue but also in deeper lying muscle.

Convex Third Ventricle: A Possible Sign for Dementia Using MRI:

The shape and thickness of the third ventricles were studied with magnetic resonance imaging in 46 patients under evaluation for memory impairment. We compared this population with 23 subjects imaged for other reasons. The study group consisted of patients with diagnoses of probable dementia of the Alzheimers type (DAT; 35.6%), multi-infarct dementia (MID; 22.2%), depression (8.9%), alcoholic dementia (6.7%), other dementias (OD; 13.2%) and no dementia (6.7%). Within the study group, there were no significant differences across diagnostic categories for duration of symptoms or level of education. Patients with DAT were, however, more impaired than others (Mini-Mental State Examination scores: DAT 14.6 [±8.2] versus MID 17.4 [±6.2] versus OD 21.2 [±6.4]). Demented subjects were more likely than nondemented individuals to have a convex third ventricle and greater wall separation. The results suggest that the shape of the third ventricle may correlate with dementia. Possibly, the dorsal medial nucleus of the thalamus is involved in the dementia.

Image processing on Macintosh II: A practical boundary finding algorithm for biomedical measurement

With increasing research interest in displaying and analyzing biomedical images, a practical personal computer based off-line image processing software would be useful. This paper describes the implementation of an image processing work station on a Macintosh II which features a novel edge detection capability useful for biomedical measurement. The boundary finding algorithm is coded in Turbo Pascal, and operates at a speed comfortable for interactive operation. Depending on the complexity of the problem, it usually takes less than a minute for the measurement of an image. The edge detection algorithm has an built-in edge detector with decision-making capability, and can be efficiently controlled by a mouse. In this way, the local accuracy of an automatic edge detection operator, and the global accuracy of the human eye (through manual control of a mouse) are combined.

Magnetic Resonance Imaging of the Presbyopic Eye

Magnetic resonance imaging (MRI) is a noninvasive process for imaging internal structures in the body. High-resolution imaging of the ciliary muscle and lens can be utilized to verify the predictions from the computer simulation model of presbyopia described by Semmlow et al. (Chapter 24). Data for this model were obtained from experiments using topically applied drugs to diminish or enhance the effectiveness of the ciliary muscle. Although the model demonstrates that the presbyopic mechanism is primarily lenticular, and that ciliary muscle change is not fundamental to this process, it does not rule out some change in ciliary muscle response as presbyopia advances. However, the relationship between ciliary muscle and lens response during presbyopia cannot be unambiguously determined by analysis of external behavior alone, such as that observed in the drug studies. High-resolution MRI could provide a direct measurement of ciliary muscle response at known levels of lens accommodation response.