Search PubMed⌕ Search

Biomedical subjects

G Laub

Publications and source records attributed to G Laub.

88 records · Page 5Linked to original sources
PubMed1989

Projection arteriography and venography: initial clinical results with MR.

Motion currently limits the applications of magnetic resonance (MR) angiography in certain regions of the body. To overcome this problem, a series of breath-hold, two-dimensional, flow-compensated gradient-echo images were acquired. These images were then processed by means of the maximum intensity projection algorithm to produce projection angiograms. The method was evaluated in 10 healthy subjects and in 12 patients and validated by comparing conventional angiograms, contrast material-enhanced computed tomographic scans, and duplex sonograms with MR projection arteriograms and venograms of the chest, abdomen, and pelvis. The aorta and pulmonary arteries and their branches were demonstrated, as was detailed anatomy of the hepatic and portal venous systems and inferior vena cava. Renal arteries and veins could be studied in both native and transplanted kidneys. The method permits determination of flow direction and differentiation of arteries and veins and is superior to three-dimensional acquisition techniques for imaging slow blood flow. Initial results suggest that the method may have clinical applications for a variety of vascular disorders.

Arteries↗
PubMed1988

In-plane vascular imaging: pulse sequence design and strategy.

Magnetic resonance (MR) angiography is a noninvasive method of obtaining images without contrast agents. Recent developments in sequence design have allowed images of moving spins to be obtained without a loss of signal by rephasing the spins with three or four gradient pulses to compensate for constant velocity or acceleration, respectively. At longer echo times (TE), this approach allowed for low readout gradients and high signal-to-noise ratios. Angiograms with a resolution of 300 micron were obtained. With additional sequences that allow some dephasing but minimal signal loss, separate images of arteries and veins were obtained. Phase information was used to estimate flow velocity. Application of the rephasing scheme to gradient-echo sequences allowed for ungated, fast MR angiograms. Acceleration correction was important for long TE sequences, but velocity-corrected, gradient-echo sequences with a very short TE were comparable to velocity- and acceleration-corrected, gradient-echo sequences with slightly longer TEs. With ungated three-dimensional, gradient-echo sequences, susceptibility artifacts were minimized and excellent contrast-to-noise ratios were obtained.

Angiography↗
PubMed1988

[High resolution MR angiography with rephasing and dephasing sequences for selective vascular imaging of arteries and veins].

With rephasing and dephasing sequences the vascular system is imaged with high or low signal intensity whereas stationary tissue is imaged with identical signal intensity. With images recorded in systole and diastole followed by image subtraction separate imaging of arteries or veins without background superposition is possible. 13 patients with vascular lesions of the lower extremities and 7 volunteers were examined. Vascular stenosis, aneurysm, dilatation, occlusion and collateral vessels could be imaged similar to digital subtraction angiography. Vessels with a diameter down to 1 mm could be imaged. The large slice thickness up to 80 mm results in projection type images where the vascular tree is imaged over the whole field of view and without partial volume effects.

Arteries↗
PubMed1987

The hemodynamics of beta-blockade in patients undergoing abdominal aortic aneurysm repair.

To assess the intraoperative and postoperative hemodynamic effects of beta-blockade and its benefits in limiting myocardial ischemia and infarction, a group of 32 patients scheduled for abdominal aortic aneurysm (AAA) surgery (group 1) was treated with oral metoprolol immediately before surgery and with intravenous metoprolol during the postoperative period. Mean age was 71 years, and mean ejection fraction was 56% (range 36% to 83%). Eight patients had a preoperative history of angina, 13 had a history of myocardial infarction, and five had electrocardiographic evidence of prior myocardial infarction. A group of 51 closely matched patients with AAA who did not receive metoprolol served as controls (group 2). In group 1, overall hemodynamic tolerance of metoprolol intraoperatively and postoperatively was good, and there was no incidence of congestive heart failure, hypotension, or asthma. Furthermore, in group 1 significant reduction of systolic blood pressure and heart rate was consistently noted at frequent intraoperative intervals and for 48 hr after surgery, with only a transient reduction of cardiac index. In group 1, only one patient (3%) suffered an acute myocardial infarction. In contrast, nine group 2 patients (18%; p less than .05) suffered perioperative myocardial infarction. Furthermore, only four (12.5%) group 1 patients developed significant cardiac arrhythmias as opposed to 29 group 2 patients (56.9%; p less than .001). These data demonstrate that beta-blockade with metoprolol is effective in controlling systolic blood pressure and heart rate both intraoperatively and postoperatively in patients undergoing repair of AAA and can significantly reduce the incidence of perioperative myocardial infarction and arrhythmias.

Aged↗
PubMedDate not supplied

Phase-contrast MR angiography with reduced acquisition time: new concepts in sequence design.

A new acquisition scheme for three-dimensional (3D) phase-contrast MR angiography reduces by 33% the measurement time for a data set sensitive to flow in all three orthogonal directions. Background suppression is achieved by acquiring a flow-compensated data set and three data sets flow encoded in the three orthogonal directions, with subsequent complex subtraction. The data are acquired in an interleaved fashion, eliminating misregistration artifacts due to patient motion between measurements sensitive to different flow directions. A standard maximum-intensity-projection algorithm is applied to the combined 3D data set to obtain angiographic projections sensitive to all three orthogonal flow directions. The theory and implementation of the method are described and examples of its application to the intracranial and abdominal circulation are provided.

Blood Vessels↗
PubMedDate not supplied

Novel application of breath-hold turbo spin-echo T2 MRI for detection of acute myocardial infarction.

To assess the clinical utility of the breath-hold turbo spin-echo T2-weighted MRI in patients with acute myocardial infarction, the results of MRI were compared with those of electrocardiography, coronary angiography, and thallium-201 single photon emission tomography (SPECT) in 23 patients and 5 healthy volunteers. To compare MRI and thallium-SPECT, the left ventricle was divided into five segments, and the presence of myocardial infarction was determined in each segment. MRI demonstrated an abnormally bright signal in 49 of 140 segments (five segments each from 23 patients and 5 volunteers); thallium-SPECT showed a fixed perfusion defect in 52 segments, for an 85% diagnostic concordance rate. The size of the myocardial infarction measured on MRI corresponded well to that measured on thallium-SPECT (r = .70, P < .01). Breath-hold turbo spin-echo T2 MRI can be used for detection of acute myocardial infarction in conjunction with thallium-SPECT, especially when accurate localization of lesion, increased spatial resolution, and anatomic landmarks are needed.

Coronary Angiography↗
PubMedDate not supplied

Single-shot T1- and T2-weighted magnetic resonance imaging of the heart with black blood: preliminary experience.

PURPOSE: To implement and evaluate two robust methods for T1- and T2-weighted snapshot imaging of the heart with data acquisition within a single heart beat and suppression of blood signal. METHODS: Both T1- and T2-weighted diastolic images of the heart can be obtained with half Fourier single-shot turbo spin echo (HASTE) and turbo fast low-angle shot (turboFLASH) sequences, respectively, in less than 350 ms. Signal from flowing blood in the ventricles and large vessels can be suppressed by a preceding inversion recovery preparing pulse pair (PRESTO). Fifteen volunteers and five patients have been evaluated quantitatively for signal-to-noise ratio (SNR) contrast-to-noise ratio (CNR) and flow void and qualitatively for image quality, artifacts, and black-blood effect. RESULTS: Both PRESTO-HASTE and PRESTO-turboFLASH achieved consistently good image quality and blood signal suppression. In contrast to gradient-echo (GRE) echo-planar imaging techniques, (EPI) HASTE and turboFLASH are much less sensitive to local susceptibility differences in the thorax, resulting in a more robust imaging technique without the need for time-consuming system tuning. Compared to standard spin-echo sequences with cardiac triggering. HASTE and turboFLASH have significantly shorter image acquisition times and are not vulnerable to respiratory motion artifacts. CONCLUSION: PRESTO-HASTE and PRESTO-turboFLASH constitute suitable methods for fast and high-quality cardiac magnetic resonance imaging (MRI).

Blood↗
PubMedDate not supplied

Fast T2-weighted liver MR imaging: comparison among breath-hold turbo-spin-echo, HASTE, and inversion recovery (IR) HASTE sequences.

BACKGROUND: To evaluate the diagnostic efficacy of fast T2-weighted magnetic resonance (MR) imaging sequences on image quality, hepatic lesion detection, and lesion conspicuity. METHODS: Three breath-hold, fast T2-weighted sequences with turbo-spin-echo (TSE), half-Fourier acquisition single-shot TSE (HASTE), and inversion recovery (IR) HASTE techniques were examined for 43 lesions in 20 consecutive patients. Evaluation was performed qualitatively on image quality and lesion detectability and quantitatively on lesion conspicuity by using lesion/liver signal-intensity and contrast-to-noise ratios. RESULTS: Artifacts were significantly less present on the HASTE sequence (p < 0.01). Both TSE and HASTE sequences detected 39 lesions (91% each); the IR HASTE sequence detected 37 (86%). IR HASTE sequence showed a significantly higher signal-intensity ratio than did the others (p < 0.01). CONCLUSIONS: Breath-hold TSE versus breath-hold HASTE or IR HASTE is still the most robust sequence in lesion detection, image quality, and lesion conspicuity. However, the HASTE sequence offers good lesion detection and image quality, and the IR HASTE has a better signal-intensity ratio.

Adolescent↗
PubMedDate not supplied

Integrated 3D display of brain anatomy and intracranial vasculature in MR imaging.

In many clinical situations neuroradiologists and neurosurgeons are keenly interested in images displaying both brain structures and intracranial vessels in an integrative manner. In this paper an approach to three-dimensional visualization of brain and vascular structures from magnetic resonance (MR) volume data is reported. It has been designed with the aim of providing a robust and reliable image processing tool for routine clinical applications. The method has been made possible by recent developments in MR image acquisition, especially MR angiography and rapid gradient-echo sequences (Turbo-fast low angle shot). On the basis of the ray-tracing principle, integration of brain and vessel anatomy into a single 3D image is achieved. Image data are acquired with flow-compensated gradient-echo pulse sequences. Even slow flow in venous structures may be demonstrated using a two-dimensional sequential-slice scanning method. Finally, if incorporated into an interactive image processing system, this technique may be used as a planning tool allowing a surgical "rehearsal" prior to actual operative exposure and resection of a lesion.

Brain↗
PubMedDate not supplied

High resolution cine MRI of vessel distension.

OBJECTIVE: We have evaluated the ability of high resolution cine MRI to quantify vessel distension. MATERIALS AND METHODS: Gradient echo imaging was used to acquire high resolution, cardiac-triggered imaging of the ascending aorta in normal volunteers to measure changes in the cross-sectional area of the lumen over the cardiac cycle. The effects of temporal resolution, spatial resolution, and the radiofrequency flip angle on the measurements were investigated. RESULTS: High spatial resolution improved the ability to detect changes in the luminal area. High temporal resolution allowed better tracking of maximal vessel distension. A small flip angle reduced the saturation of slow flow observed in imaging acquired using a large flip angle. CONCLUSION: Our study has demonstrated that high spatial resolution and high temporal resolution can substantially improve the measurement of vessel distension. We have overcome problems of intravoxel dephasing and spin saturation by using high spatial resolution, a short echo time with flow compensation, and a small flip angle.

Blood Vessels↗
PubMedDate not supplied

Application of spatial modulation of magnetization to cervical spinal stenosis for evaluation of the hydrodynamic changes occurring in cerebrospinal fluid.

OBJECTIVE: To evaluate the hydrodynamic changes occurring in cerebrospinal fluid (CSF) flow in cervical spinal stenosis using the spatial modulation of magnetization (SPAMM) technique. MATERIALS AND METHODS: Using the SPAMM technique, 44 patients with cervical spinal stenosis and ten healthy volunteers were investigated. The degree of cervical spinal stenosis was rated as low-, intermediate-, or high-grade. Lowgrade stenosis was defined as involving no effacement of the subarachnoid space, intermediate-grade as involving effacement of this space, and high-grade as involving effacement of this space, together with compressive myelopathy. The patterns of SPAMM stripes and CSF velocity were evaluated and compared between each type of spinal stenosis and normal spine. RESULTS: Low-grade stenosis (n = 23) revealed displacement or discontinuity of stripes, while intermediate- (n = 10) and high-grade (n = 11) showed a continuous straight band at the stenotic segment. Among low-grade cases, 12 showed wave separation during the systolic phase. Peak systolic CSF velocity at C4-5 level in these cases was lower than in volunteers (p <.05), but jet-like CSF propulsion was maintained. Among intermediate-grade cases, peak systolic velocity at C1-2 level was lower than in the volunteer group, but the difference was not significant (p >.05). In high-grade stenosis, both diastolic and systolic velocities were significantly lower (p <.05). CONCLUSION: Various hydrodynamic changes occurring in CSF flow in cervical spinal stenosis were demonstrated by the SPAMM technique, and this may be a useful method for evaluating CSF hydrodynamic change in cervical spinal stenosis.

Cervical Vertebrae↗
PubMedDate not supplied

Contrast-enhanced MR angiography at 3T in the evaluation of intracranial aneurysms: a comparison with time-of-flight MR angiography.

The combination of 3T and parallel-acquisition techniques holds promise for improved performance of contrast-enhanced MR angiography (MRA), in terms of speed, spatial resolution, and coverage. We present a comparison of 2 MRA techniques, including time-of-flight (TOF) and contrast-enhanced MRA, for detection and evaluation of intracranial aneurysms. Our results show that contrast-enhanced MRA with highly accelerated parallel acquisition at 3T does not have the known drawbacks of TOF-MRA techniques, including prolonged acquisition time, spin saturation, and flow-related artifacts, with comparable aneurysm characterization.

Aged↗
PubMedDate not supplied

Intracranial MR angiography: a direct comparison of three time-of-flight techniques.

During the past few years, several time-of-flight MR angiographic techniques have been described for rapid, reliable, noninvasive vascular evaluation. This investigation was performed to directly compare three time-of-flight methods in imaging the intracranial vasculature: a single-volume method, a sequential two-dimensional slice technique, and a technique using the sequential acquisition of multiple thin volumes. Thirty-two normal volunteers were imaged, and direct comparisons of the three techniques were performed in 20 subjects. Analysis of the resulting images revealed optimal depiction of large vessels with the single-volume and multiple thin-volume methods, small vessels with the multiple thin-volume technique, and venous structures with the sequential two-dimensional slice acquisition. The effects of progressive spin saturation in time-of-flight MR angiography are discussed along with the individual benefits and disadvantages of each method. We conclude that the diagnostic value of intracranial time-of-flight MR angiography can be maximized through tailoring the angiographic method to the suspected abnormality based on the requirements for spatial resolution and slow-flow sensitivity, as suggested by the clinical history or prior imaging studies.

Cerebral Arteries↗