Biomedical subjects

A C Eichenberger

Publications and source records attributed to A C Eichenberger.

6 recordsLinked to original sources

PubMed1995

Detection of liver metastases: comparison of superparamagnetic iron oxide-enhanced and unenhanced MR imaging at 1.5 T with dynamic CT, intraoperative US, and percutaneous US.

PURPOSE: To compare the sensitivities of superparamagnetic iron oxide-enhanced and unenhanced magnetic resonance (MR) imaging at 1.5 T with those of percutaneous ultrasound (US), intraoperative US (IOUS), and dynamic computed tomography (CT) in the preoperative assessment of metastatic liver disease. MATERIALS AND METHODS: Eighteen patients with liver metastases who were candidates for curative surgery underwent presurgical imaging. Thirteen patients underwent surgery and IOUS after undergoing preoperative US, CT, and MR imaging. RESULTS: In the preoperative imaging group, the standard of reference was the total number of lesions detected with any of the modalities. Superparamagnetic iron oxide-enhanced MR imaging was the most sensitive modality (99%). In the surgical group, the standard of reference was the total number of metastases identified at IOUS and pathologic examination. IOUS had the highest sensitivity (80%), followed by superparamagnetic iron oxide-enhanced MR imaging (56%). CONCLUSION: Superparamagnetic iron oxide-enhanced high-field-strength MR imaging facilitates the preoperative evaluation of potentially curable metastatic liver disease; however, it is inferior to IOUS.

Colorectal Neoplasms↗

PubMed1994

Normal heart: evaluation with echo-planar MR imaging.

PURPOSE: To evaluate the appearance of the heart on spin-echo (SE) and gradient-echo (GRE) echo-planar magnetic resonance (MR) images. MATERIALS AND METHODS: Nine healthy volunteers were examined with an MR imager with transaxial echo-planar imaging (EPI) capabilities. SE EPI and GRE EPI sequences were used. Full k-space signal was obtained with readout time of 40 msec per image, and total image acquisition time was 72 and 52 msec, respectively, for SE EPI and GRE EPI. RESULTS: Delineation of cardiac structures was superior with SE EPI, reflective of significantly higher contrast between myocardial and intraluminal signal intensity (SI) (P < .001). The higher (P < .01) and more homogeneous (P < .001) intraluminal SI with GRE EPI allowed better assessment of intracardiac flow. Septal SI was significantly higher for GRE EPI (P < .01), but signal homogeneity was similar for both sequences (P > .2). CONCLUSION: Diagnostic images of the heart were obtained with both SE EPI and GRE EPI. GRE EPI is more suitable for flow studies because of the higher and more homogeneous intravascular SI.

Adult↗

PubMed1993

Aortic valve pressure gradients in patients with aortic valve stenosis: quantification with velocity-encoded cine MR imaging.

OBJECTIVE: Pressure gradients across the aortic valve due to stenosis of the valve must be measured accurately to evaluate the functional severity of the stenosis. Velocity-encoded cine MR has been used to quantify blood flow and flow direction and, more recently, the regurgitant fraction in aortic regurgitation. The purpose of this study was to determine the feasibility and accuracy of velocity-encoded cine MR for estimating pressure gradients across the aortic valve in patients with aortic stenosis. SUBJECTS AND METHODS: We used velocity-encoded cine MR to measure flow velocity and determine pressure gradients across the aortic valve in 19 subjects. The pressure gradient (delta P) was estimated from the simplified Bernoulli equation by using the maximum instantaneous aortic jet velocity (Vmax): delta P (mm Hg) = 4V2max (m/sec). RESULTS: Maximum and mean systolic pressure gradients determined by using velocity-encoded cine MR were 3-148 mm Hg and 2-87 mm Hg, respectively, for all subjects. The pressure gradients correlated closely with gradients determined by using established methods: Doppler echocardiography and cardiac catheterization. Correlation coefficients (r) were .96 (y = 0.94x - 1.9) and .97 (y = 0.97x + 0.5), respectively. CONCLUSION: We conclude that velocity-encoded cine MR imaging provides a noninvasive and accurate means for quantifying the severity of valvular aortic stenosis. MR is a feasible method for determining pressure gradients across the aortic valve.

Adult↗

PubMed1992

Magnetic resonance imaging of the heart and the great vessels: morphology, function, and perfusion.

The capability of MR imaging to evaluate cardiovascular disease is developing faster than ever, as is well documented by the numerous contributions that have been made to the literature during the past year. As the field progresses, MR imaging will probably become one of the preferred investigational methods for the evaluation of cardiac function. The first stage of MR imaging development emphasized replication of commonly used methods for studying morphology and analyzing global ventricular performance. Thus, validated MR imaging methods exist for the assessment of ventricular' volume, ejection fraction, and mean wall stress. More recently, emphasis has been directed toward the evaluation of regional function and perfusion, using novel methods and attracting increasing interest from the cardiovascular research community. Studies reviewed here focus on both clinical results obtained using well-established MR imaging techniques and new results using innovative methods, further extending the usefulness of MR imaging. Topics discussed include congenital and ischemic heart disease and disease of the great vessels. Technical advances in flow and velocity mapping and in the evaluation of ventricular performance are also discussed.

Aortic Diseases↗

PubMedDate not supplied

Ischemic heart disease: assessment with gadolinium-enhanced ultrafast MR imaging and dipyridamole stress.

The potential of magnetic resonance (MR) imaging for the detection of myocardial perfusion abnormalities in patients with coronary artery disease has not been fully explored. A feasibility study was conducted in 10 patients with a novel approach to determine whether myocardial ischemia can be assessed with MR imaging and dynamic first-pass bolus tracking enhanced with gadolinium tetraazacyclododecanetetraacetic acid (DOTA). Three tomographic planes were acquired before and after pharmacologic stress with dipyridamole, with use of the bolus-tracking series at rest as a reference. The change in myocardial rate of enhancement was compared with the results obtained by means of the established methods, exercise thallium scintigraphy and coronary angiography. Detection of ischemic regions with MR imaging showed a sensitivity, specificity, and diagnostic accuracy of 65%, 76%, and 74%, respectively. Ultrafast MR imaging can be used to detect regions of myocardial ischemia.

Adult↗

PubMedDate not supplied

Phase-contrast echo-planar MR imaging: real-time quantification of flow and velocity patterns in the thoracic vessels induced by Valsalva's maneuver.

Although the clinical manifestations of Valsalva's maneuver are well known, the associated hemodynamic changes in the great vessels have not been extensively studied and documented. In each of six healthy subjects, we evaluated three "quasi-steady-state" phases of Valsalva's maneuver: (1) during normal respiration, (2) during late strain, and (3) 4 seconds after strain release. Continuous flow, velocity, and cross-sectional area measurements were obtained in the superior vena cava, pulmonary trunk, and thoracic aorta with single-shot echo-planar MR imaging (EPI) with velocity-encoded gradients, which provided 256 images in 5 seconds, yielding 26 velocity-encoded images per second. In the superior vena cava, Valsalva's maneuver induced an 11% decrease in average flow volume, a 102% increase in peak flow velocity, a 156% increase in the time velocity integral, and a 37% decrease in cross-sectional area. MR velocity measurements agreed with echocardiographic data and supplied additional information on flow and morphology. EPI showed a reduction in venous return during Valsalva's maneuver by simultaneously assessing flow, velocity, and vessel morphology; this technique appears to be useful in the analysis of flow dynamics of the great vessels.

Adult↗