Biomedical subjects
Publications and source records attributed to R R Edelman.
Although further work is needed to improve spatial resolution and flow contrast as well as to lessen dependence on a regular cardiac rhythm, the potential clinical utility of MR coronary angiography is substantial. For the first time, information regarding coronary artery anatomy can be acquired in a completely noninvasive manner.
K-space segmentation can be used to produce both black-blood and bright-blood images that improve visualization of blood vessels in the presence of disturbed or time-varying flow. When used judiciously, these techniques can serve as effective problem-solving tools in clinical situations in which alternative techniques are prone to error.
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In abdominal aortic aneurysm ultrasonography, contrast-enhanced CT, and digital subtraction angiography (DSA) are the preoperative diagnostic methods of choice accepted today. It was the goal of this study to evaluate time-of-flight magnetic resonance angiography (MRA) in comparison with other radiographic procedures in different types of aneurysms. In 24 patients with proven aortic aneurysm, projection angiograms (MIP algorithm) of the abdominal aorta and pelvic arteries were performed using two-dimensional gradient echo multi slice sequence (FLASH, TE/TR = 10/51 ms; three slices; breathhold technique; flip angle = 30 degrees) in coronal orientation. In addition, renal arteries were imaged in axial slices. The information provided by MRA was comparable to that of DSA (perfused vascular lumen) and contrast-enhanced CT (alteration of vascular wall). Thus dilatation, thrombus, dissection, or inflammation could be analysed safely. Extension of the aneurysm to pelvic arteries could be evaluated in most cases by rotation of the projection angiograms; ostial renal artery disease could be visualized on axial slices. If further technical improvement of MRA is presupposed, this noninvasive method may completely replace the invasive procedures of contrast-enhanced CT and DSA in the future.
Despite the availability of numerous noninvasive tests to identify those with inducible myocardial ischemia, 20% of conventional contrast angiograms demonstrate no significant coronary artery stenoses. Magnetic resonance (MR) imaging is ideally suited for evaluation of the heart, and has already been shown to be highly accurate for the depiction and assessment of cardiac chamber size, ventricular function, and valvular insufficiency. Using conventional spin-echo and gradient-echo techniques, investigators have previously been able to characterize coronary artery bypass grafts as "patent" or "occluded," but visualization of large segments of the native coronary vessels was unsuccessful due to artifacts related to cardiac and respiratory motion. Recently, several new "fast imaging" breath-hold techniques, including k-space segmentation and spiral imaging, have shown great promise for both visualizing the native coronary arteries, assessing vessel patency, and quantifying coronary blood flow. Echo planar MR coronary angiography also appears to be feasible. Further software and hardware improvements are needed, but MR may soon prove to be the premier cardiac imaging technique by providing a comprehensive cardiac evaluation for those with suspected coronary artery disease, including information previously unobtainable by any other noninvasive test.
In only a few years magnetic resonance angiography has evolved to a clinically useful tool. In many situations it can resolve questions which used to be addressed by conventional contrast angiography, such as carotid stenoses, aneurysms, arteriovenous malformations, and venous and sinus disorders. In addition, selective magnetic resonance angiography provides information on direction and origin of flow and circulation in vessels serving as collaterals.
Portal vein thrombosis (PVT) is a rare condition that affects both children and adults. This article reviews the existing literature on PVT, with an emphasis on recent developments. A comprehensive description of etiologic factors and clinical aspects is presented. Treatment issues that remain unresolved are addressed and a framework for the diagnostic work-up and management of patients with PVT is provided.
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The value of a fast imaging sequence in diagnosing focal liver lesions was assessed in 43 patients. The sequence (TurboFLASH with segmented acquisition) allows the acquisition of T1- and T2-weighted images within a breath-hold interval. Lesion-liver contrast was compared with T2-weighted spin-echo, T1-weighted gradient-echo, and single shot TurboFLASH sequences. All lesions that were seen with the latter sequences were also visible on the segmented TurboFLASH images. Contrast on the segmented TurboFLASH images was similar to that of T2-weighted spin-echo sequences and superior to T1-weighted gradient-echo sequences. Signal of fat could be nulled at an inversion time of 10 ms, signal from liver tissue could be nulled at an inversion time of 300 ms. By minimising the liver signal, the lesions could be "highlighted". This was not possible with the other imaging sequences. The segmented TurboFLASH technique allows breath-hold imaging of the liver with arbitrary image contrast. The lesion-liver contrast is comparable to time-consuming T2-weighted spin-echo sequences.
The staging of renal cell carcinoma (RCC) comprises exclusion of tumour expansion into the renal veins and the inferior vena cava (IVC). In 44 patients with RCC these vessels were examined using MRA on the basis of "time-of-flight" technique (coronal/axial 2D GE-flash-sequence, MIP-algorithm). The method was evaluated against contrast-enhanced CT and DSA in normal conditions and tumour-involved IVC (n = 12) and renal veins (n = 32) respectively. Following analysis of projection-angiograms (PA) and individual slices the results of MRA without contrast material included an information on vascular tumour extension that was identically safe as CT and DSA. In coronal slice orientation tumour extension into the vena cava was proven in 100%, and into the renal veins in 84%. Additional axial slices were necessary to demonstrate tumour extension into the renal veins in unclear cases. Single slices showed to be superior to PA for a correct identification of the size of the tumour thrombus.
Magnetic resonance angiography (MRA) is an accurate non-invasive tool for imaging the cerebral vessels. It provides morphologic information about the cerebral vessels relying on blood flow as the physical basis for generating contrast between stationary tissues and moving spins. 'Selective' MRA gives functional information about the cerebrovascular system such as flow direction, origin of flow, and presence or absence of collaterals. Arteries and veins can be imaged selectively due to their usually opposite flow directions. Although at a relatively early stage of development, MRA has already become a widely used tool for the study of the cerebrovascular system.
With the increasing application of magnetic resonance imaging (MRI) and MR angiography in parenchymal liver disease, methods are becoming more widely available for noninvasive measurement of visceral blood flow. Amplitude-based (time-of-flight) and phase-based techniques have proved effective for measurement of portal blood flow, and phase-sensitive methods are applicable to arterial flow measurements. Because respiratory motion degrades the quality of examinations in the abdomen, it is desirable to use methods that can generate flow information in a breath-hold period. Although substantial technical difficulties persist for quantitative arterial flow measurements in the abdomen, the technical requirements for venous flow are less stringent, and important clinical information can be derived using straightforward techniques. The authors describe the principles of flow measurement using time-of-flight and phase methods in visceral arteries and veins, and discuss their practical implementation. Clinical applications are discussed, based on the experience of the authors and others working in the field.
Dynamic contrast-enhanced T2-weighted magnetic resonance (MR) imaging and MR angiography (MRA) were used to evaluate cerebral blood volume and the intracranial arterial system in 34 patients within 48 hours after the onset of cerebral ischemia. In 24 of the patients, an abnormality identified on T2-weighted images corresponded to the acute clinical deficit. Intracranial MRA demonstrated occlusions or severe stenoses of major vessels supplying the area of infarction in 16 of these patients, and decreased blood volume correlated well with MRA abnormalities. Infarcts less than 2 cm in diameter were not reliably shown with MRA or blood volume studies. Correlation between lesions seen with MRA and decreased blood volume in acute infarcts was good, and both techniques demonstrated lesions early in the clinical course. By providing information about hemodynamics not available with conventional T1- or T2-weighted images, MRA and dynamic MR imaging could prove helpful in describing the pathophysiologic characteristics of stroke and in guiding early therapeutic intervention.
Dye dilutional techniques are widely accepted for the assessment of intracardiac shunts, but current techniques require arterial access or radioisotope injection. Ultrafast (less than 500 msec) magnetic resonance (MR) imaging is ideally suited for the evaluation of an indicator during passage through the heart. Twenty patients were studied, including 13 with shunts. Four-chamber, T1-weighted images were obtained during bolus injection of gadopentetate dimeglumine. A single image was obtained in 420 msec, with repetitive images acquired after each QRS complex. After the contrast material was injected, there was pronounced signal intensity enhancement in the right atrium, followed by the right ventricular cavity, left atrium, left ventricular cavity, and descending aorta. Patients with substantial intracardiac shunts demonstrated early recirculation. First-pass contrast material-enhanced MR imaging is a promising new technique for the rapid assessment of intracardiac shunts. Combined with anatomic and functional MR imaging techniques, it can help provide a comprehensive noninvasive evaluation of suspected intracardiac shunts or provide follow-up in patients with known shunts.
The authors hypothesized that magnetization transfer contrast (MTC) could be used to improve flow contrast in time-of-flight (TOF) magnetic resonance (MR) angiography. Two- and three-dimensional flow-compensated gradient-echo images were obtained with and without MTC. MTC images were obtained by applying low-power radio-frequency (RF) radiation with a frequency offset from the bulk "free" water resonance frequency before the excitation RF pulse. The signal intensity of stationary tissue decreased as the power applied for the MTC pulse was increased. A smaller decrease occurred in venous signal intensity as measured in the superior sagittal sinus, and less change was seen in the arterial signal intensity as measured in the middle cerebral artery. Cerebrospinal fluid showed no MTC effect. The use of MTC improved small-vessel depiction on maximum-intensity projection images. The authors conclude that use of MTC can substantially enhance the quality of TOF MR angiography of the brain.
In this prospective blinded study of inferior vena caval (IVC) patency, 18 patients underwent 25 duplex ultrasound (US) and magnetic resonance (MR) angiography examinations over an eight-month period following Simon nitinol filter placement. Clinical examination for lower extremity venous stasis and plain abdominal radiography were also performed. Twenty-three of 24 MR examinations and 11 of 24 US examinations were judged technically adequate by the blinded observers. One technically adequate US exam was false positive for intraluminal caval thrombus. Thirteen technically inadequate US examinations missed 3 complete caval occlusions and 2 partial occlusions. MR identified all patients with complete or partial caval occlusion. The authors conclude that duplex US reliably confirms IVC patency only when strict criteria for technical adequacy and interpretation are met (good visualization of filter and IVC above and below filter). MR, although expensive, more reliably identifies nonoccluding intraluminal thrombus and caval occlusion. It should be the noninvasive study of choice in symptomatic patients with venous stasis and patients with recurrent pulmonary emboli.
Rapid MRI of the molecular diffusion of water demonstrated cerebral infarcts in 32 patients. We studied these patients at various times following the onset of ischemic symptoms and found that diffusion-weighted imaging revealed the infarcts sooner than conventional T2-weighted spin-echo imaging did; four hyperacute infarcts were shown only by diffusion-weighted imaging. Acute infarcts had lower apparent diffusion coefficients (ADCs) than noninfarcted regions did. This relative difference in ADC reached a nadir in the first 24 hours and rose progressively thereafter. Chronic infarcts showed a relative increase in diffusion and were readily distinguishable from acute infarcts. The technique takes less than 2 minutes to apply using a standard 1.5-tesla scanner in the clinical setting. Diffusion-weighted imaging has the potential to play a role in improving the early anatomic diagnosis of stroke and therefore in the development and implementation of early stroke interventions.
The clearly documented transaqueductal migration of a solitary intraventricular neurocysticercus cyst is described. The cyst was fortuitously demonstrated on magnetic resonance imaging during migration through the aqueduct. The radiological appearance and clinical significance of this condition are discussed.