Biomedical subjects

G Laub

Publications and source records attributed to G Laub.

At least 55 records · Page 3Linked to original sources

PubMed1998

[First clinical results of ultrafast, contrast-enhanced 2-phase 3D-angiography of the abdomen].

PURPOSE: To assess the utility of breath-hold abdominal ultrafast three-dimensional (3D) gadolinium-enhanced dual-phase magnetic resonance angiography (MRA). MATERIAL AND METHODS: 125 patients with various abdominal pathologies were imaged using a breath-hold ultrafast gadolinium-enhanced dual-phase 3D-MRA technique. RESULTS: 119 (95%) of 125 MRA's were of good or excellent quality. The sensitivity in the detection of renal artery stenoses as well as stenoses of the celiac trunk and the superior mesenteric artery was 100%. Accessory renal arteries (n = 9) and replaced hepatic arteries (n = 4) were reliably detected by MRA. In 24 (71%) of 34 cases MR-angiographic delineation of the spleno-portal system and hepatic veins was superior compared to conventional angiography. CONCLUSION: Breath-hold gadolinium-enhanced dual-phase 3D-MRA has the potential to replace conventional angiography in the abdomen.

Abdomen↗

PubMed1998

Patency of coronary bypass grafts: assessment with breath-hold contrast-enhanced MR angiography--value of a non-electrocardiographically triggered technique.

PURPOSE: To determine the value of non-electrocardiographically triggered contrast material-enhanced magnetic resonance (MR) angiography in assessing the patency of venous and internal thoracic artery (ITA) grafts after coronary bypass surgery. MATERIALS AND METHODS: Twenty-seven patients with 76 coronary bypass grafts (48 venous, 28 ITA) were examined 26.5 months +/- 5.8 after surgery with MR angiography and conventional angiography. MR angiography was performed with a three-dimensional gradient-echo sequence after automated injection of contrast material; contrast agent administration was based on measurement of the individual transit time of the agent. Results of MR angiography were interpreted by two independent observers and compared with results of conventional angiography. RESULTS: The independent interpretations of the MR angiograms agreed with the results of conventional angiography in 96% and 91% of the grafts. After a final consensus reading, sensitivity was 95% for all grafts, 94% for venous grafts, and 96% for ITA grafts. Specificity was 85% for venous grafts and 67% for ITA grafts. Positive predictive value was 95% for all grafts, 94% for venous grafts, and 96% for ITA grafts. CONCLUSION: Non-electrocardiographically triggered contrast-enhanced MR angiography allows reliable assessment of the patency of venous and arterial coronary bypass grafts.

Adult↗

PubMed1998

Breath-hold gadolinium-enhanced MR angiography of the major vessels at 1.0 T: dose-response findings and angiographic correlation.

PURPOSE: To find the appropriate contrast agent dose for gadolinium-enhanced magnetic resonance (MR) angiography by using individual measurement of contrast agent transit times in a randomized study. MATERIALS AND METHODS: A total of 34 patients with disease of the aorta or its major branches or both were randomly assigned to receive a dose of 0.1, 0.2, or 0.3 mmol of gadopentetate dimeglumine per kilogram of body weight. Initially, contrast agent transit times were measured with use of a turbo fast-low-angle-shot sequence. Subsequently, a three-dimensional fast imaging with steady-state precession sequence (7.3-msec repetition time, 2.8-msec echo time) was used for breath-hold MR angiography. Gadopentetate dimeglumine was injected with an MR-compatible power injector. Efficacy was evaluated by measurement of vessel enhancement and by clinical correlation of MR angiograms with x-ray angiograms. RESULTS: Evaluation of contrast agent transit time was possible in all patients with the test doses, which provided contrast-enhanced MR angiograms of constant quality. Neither vessel enhancement nor diagnostic information was significantly different across the these study groups. CONCLUSION: The clinical gadolinium dose of 0.1 mmol/kg is sufficient for diagnostic assessment of the aorta and its major branches at contrast-enhanced MR angiography. High-dose studies appear not to be required for these large vessels.

Adult↗

PubMed1997

Usefulness of respiratory gated magnetic resonance coronary angiography in assessing narrowings > or = 50% in diameter in native coronary arteries and in aortocoronary bypass conduits.

Magnetic resonance coronary angiography (MRCA) is a promising method for the assessment of proximal coronary artery stenosis. Conventional 2-dimensional techniques require repetitive breath holds to image multiple sections. This may lead to misregistrations if the respiratory level is not exactly reproduced. In the present study, MRCA was performed using a 3-dimensional approach with navigator echo-based respiratory gating. In 73 patients (55 men and 18 women) who were referred for cardiac catheterization, the assessment of significant stenoses (> or = 50%) was performed in the proximal and midsegments of the coronary arteries after multiplanar reconstruction of the visualized coronary arteries. In addition, in 8 patients with coronary artery bypass grafts the patency of the transplants was evaluated. After withdrawing 8 patients from analysis because of poor image quality, stenosis evaluation was possible in 236 of 455 reviewed coronary segments (52%). In the other 219 cases, either the visualization of the vessel segment was indistinct (30%) or the segment was located outside the imaging volume (18%). In total, 28 of 43 significant coronary stenoses could be correctly identified (65%). Evaluation of bypass graft patency was possible in 7 patients. All 4 occluded and 13 of 15 patent grafts were correctly classified. Thus, respiratory gated MRCA is a feasable method for the assessment of hemodynamically significant coronary stenoses and bypass graft patency. However, technical improvements are mandatory to improve accuracy of the method.

Adult↗

PubMed1997

Gadolinium-enhanced magnetic resonance angiography of the pelvis in patients with erectile impotence.

This study evaluated the potential of contrast-enhanced digital-subtraction magnetic resonance angiography (CE-DS-MRA) for noninvasive angiographic delineation of the arterial supply of the penis in patients with erectile dysfunction. After induction of an erection with prostaglandin E, a three-dimensional fast imaging with steady-state precision (FISP) sequence with TE of 1.8-2 milliseconds, TR of 4.4-5 milliseconds, and flip angle of 40 degrees-60 degrees was used to obtain high-resolution angiograms of the pelvis and penis during the injection of gadolinium diethylenetriaminepentaacetic acid (Gd-DTPA) 0.3 mmol/kg body weight, within 30-50 seconds. DS maximum intensity projections (MIPs) and multiplanar reconstructions (MPRs) were compared with clinical work-up and directional Doppler ultrasound in 11 patients. In all 11 patients (100%), the arterial supply of the penis could be delineated from the aortic bifurcation via the iliac and internal pudendal arteries to the dorsal and deep penile arteries. Of the 22 internal pudendal arteries, 6 (27%) were occluded on CE-DS-MRA and 5 (23%) had stenoses, of which 4 (18%) were greater than 50%. In 7 patients (64%) good correlation between CE-DS-MRA and clinical findings and/or Doppler ultrasound was found; in 2 patients (18%), the correlation was moderate, and in 2 patients (18%) results were discrepant. In 6 patients (55%), MRA provided additional information to the clinical and Doppler ultrasound work-up. CE-DS-MRA can delineate small vessels such as the internal pudendal and penile arteries and thus has the potential to become a noninvasive angiography method in the work-up of erectile impotence.

Arteries↗

PubMed1997

[Contrast medium enhanced magnetic resonance angiography. Theory, technique and practical implementation].

Contrast enhanced (CE) magnetic resonance angiography affords angiographic depiction of extended vascular territories with high quality and diagnostic value. A prerequisite is the fast acquisition of a three-dimensional gradient-echo data set during the injection of a bolus of a T1-shortening contrast agent. We describe the dependence of the quality of CE-MRA on technical parameters of different MR-scanners and consider some fundamental facts and practical guidelines concerning the contrast agent injection.

Cardiovascular Diseases↗

PubMed1997

[Gadolinium-enhanced magnetic resonance angiography of abdominal blood vessels].

Contrast enhanced (CE) magnetic resonance angiography (MRA) provides high resolution angiograms within 20-40 sec. The technique is based on the acquisition of heavily T1-weighted three-dimensional (3D) gradient-echo data sets (FISP) with ultrashort echo-(< 2ms) and repetition times (< 5 ms) during arterial phase of an intravenously injected bolus of a T1-shortening agent such as Gd-DTPA. For MR-angiography of abdominal vessels CE-MRA is better suited than "time-of flight" (TOF) and phase-contrast (PC) MRA because motional artifacts can be obviated with breath-held acquisitions. We have optimised the technique and evaluated its potential for angiography of the abdominal aorta and its branches as well as the portal vein and its tributaries. Whilst CE-MRA provides reliable diagnostic accuracy in the aorta and the proximal sections of its branches, small peripheral arteries cannot be assessed accurately. The portal vein and its tributaries can often be depicted better with CE-MRA than with conventional angiography but, like conventional angiography, CE-MRA is hampered by slow and reversed flow, conditions under which TOF or "true FISP" MRA may perform bst. We have also investigated FLASH-echo-planar imaging (EPI) hybrid techniques, a further technical development which due to shorter acquisition times of 12-15 sec. allows semi-dynamic imaging of the arterial and venous phase and provide better vessel contrast due to the use of fat-suppression.

Abdomen↗

PubMed1997

[Contrast media enhanced magnetic resonance angiography for determining patency of a coronary bypass. A comparison with coronary angiography].

AIM: Assessment of graft patency with current non-invasive MRA techniques is particularly difficult for evaluating internal mammary artery grafts. Our aim is to determine the accuracy of a contrast enhanced MRA technique is assessing graft patency. METHODS: We examined 19 patients with a total of 53 grafts (32 venous/21 arterial), using an ultrafast contrast enhanced 3D gradient-echo technique and compared this with the results of selective angiography. RESULTS: Sensitivity of the contrast enhanced method was 95.2% for venous grafts, 94.4% for IMA grafts and 94.8% overall. Specificity was 85.7% overall, 90.9% for venous and 66.7% for IMA grafts. Positive predictive value was 94.4%. CONCLUSION: Compared with previous studies, visualisation of IMA grafts was improved by using contrast enhanced MRA. In this preliminary study, contrast enhanced MRA proved promising for the assessment of graft patency.

Adult↗

PubMed1997

Visualization of the coronary arteries in three-dimensional reconstructions using respiratory gated magnetic resonance imaging.

OBJECTIVE: To assess the applicability of respiratory-gated magnetic resonance coronary angiography, combined with three-dimensional image reconstruction, for visualizing the coronary arteries. METHODS: Twenty subjects (three healthy volunteers and 17 patients without stenoses detected by coronary angiography) were investigated. Magnetic resonance imaging was performed in a 1.5 T scanner using ECG-triggered gradient-echo sequences to acquire a volume data set consisting of 24-48 contiguous axial cross-sections of the heart (2 mm slice thickness, 1.17 mm x 1.17 mm in-plane resolution). Navigator-echo-based retrospective respiratory gating was used to minimize respiratory motion artifacts. Three-dimensional reconstructions of the heart were rendered using surface-display techniques. The length of the visualized coronary arteries was measured in curved multiplanar reconstructions. RESULTS: In the three-dimensional reconstructions, the left main artery (LMA) and left anterior descending artery (LADA) were visualized in 17 cases, the left circumflex artery (LCXA) in 15, and the right coronary artery (RCA) in 16 cases. Vessel continuity was uninterrupted in all 17 cases for the LMA, in 14 for the LADA, eight for the LCXA, and 13 for the RCA. The mean lengths of the visualized vessels were 14 +/- 7 mm for the LMA, 65 +/- 13 mm for the LADA, 45 +/- 16 mm for the LCXA, and 37 +/- 26 mm for the RCA. Reasons for impaired visibility of the LCXA and RCA were poor image quality due to there being a low contrast:noise ratio, motion artifacts, and incomplete coverage by the imaging volume. CONCLUSIONS: Navigator-echo-based magnetic resonance imaging is a promising technique for investigating the coronary arteries. Acquisition of a volume data set permits three-dimensional displays of the coronary vessels.

Case-Control Studies↗

PubMed1996

Breath-hold MR imaging of focal liver lesions: comparison of fast and ultrasound techniques.

The performance of breath-hold MR imaging using two T2-weighted hybrid sequences (TSE, TGSE), two T2-weighted single-shot sequences (HASTE, EPI-SE), and one T1-weighted gradient-echo sequence (FLASH) was compared with a standard conventional T2-weighted SE sequence in 20 patients with focal liver lesions. Liver signal-to-noise ratio was highest for the FLASH sequence (54.3 +/- 8.3) and the HASTE (41.1 +/- 12.5) sequence, whereas the highest spleen-liver contrast-to-noise ratio was obtained by the TSE sequence (38.9 +/- 20.7). Lesion-liver CNR was highest with the TSE sequence (63.9 +/- 21.4). With both TSE and HASTE significantly (p < 0.01) more lesions were detected as compared with SE and EPI-SE sequences. Our results indicate that breath-hold TSE and HASTE sequences will eventually replace conventional T2-weighted SE techniques, due to their insensitivity to motion artifacts, superior lesion detectability and inherently short acquisition times.

Adult↗

PubMed1996

Left ventricular radial tagging acquisition using gradient-recalled-echo techniques: sequence optimization.

Myocardial tagging with magnetic resonance (MR) imaging offers unique possibilities for noninvasive left ventricular (LV) strain analysis. True three-dimensional strain analysis can be achieved with tags implemented in cardiac short axis and long axis images. Spin-echo (SE) techniques have been used for these studies. However, this approach is time-consuming: images at different phases of the cardiac cycle have to be obtained in successive measurements and hence the total number of measurements equals the number of time frames. Moreover, the images are often degraded by flow and motion artifacts. The purpose of this study was to optimize a faster and more robust MR tagging sequence for use on a clinical whole-body 1 T MR system with optimal persistence of the tags during the entire cardiac cycle. The tagging pulses were implemented in gradient-recalled-echo (GRE) sequences and compared to SE-based acquisitions. The effects of the use of flow-compensating gradients, the excitation angles, and the angles of the saturation pulses have been studied with MR signal simulations and in comparative measurements in volunteers. GRE acquisitions with flow-compensating gradients are robust techniques for myocardial tagging acquisitions. Use of optimized flip angles and saturation pulses can significantly improve delineation of the tag and can be used up to at least 700 ms after the R-wave. Therefore, LV tagging with GRE acquisitions using optimized MR parameters is a robust and promising technique.

Heart↗

PubMed1996

Evaluation of K-space segmented cine sequences for fast functional cardiac imaging.

RATIONALE AND OBJECTIVES: In functional cardiac magnetic resonance imaging, reduction of measuring time is very important for many patients who are not able to rest motionless for long-lasting examinations. In this study, the image quality of sequences with k-space segmented data recording was compared with conventional gradient-echo sequences for cine imaging with flow compensation in applications on patients with normal and reduced ejection fractions. METHODS: Thirty-one subjects (4 volunteers and 27 patients with cardiac diseases) were examined using different techniques for cine imaging of the left and right ventricles. The ejection fraction in the patients was calculated based on images of a conventional two-dimensional gradient-echo technique using a biplane ellipsoid model. The results from k-space segmented methods (3 to 9 Fourier lines per cardiac cycle for each phase image) were compared with the conventional images of the same short-axis view separately for groups of subjects with normal and reduced ejection fraction. The contrast between blood and myocardium at several sites of the heart and the homogeneity of the blood signal in the ventricle were evaluated for several phases of the heart cycle. RESULTS: The segmentation in the acquisition of raw data allows reduction of measuring time to approximately 20% to 40% of the time required for conventional sequences in cine imaging of the heart. In patients with normal or only slightly reduced heart function (ejection fraction > or = 60%) the image quality of k-space segmented sequences was not significantly different from the conventionally recorded images. In contrast, patients with markedly lowered ejection fraction (< 60%) showed degraded results of the k-space segmented sequences compared with the conventional sequence (P < 0.001). The anterolateral border and the right ventricle especially were not sufficiently delineated by the k-space segmented sequences in these patients. CONCLUSION: The k-space segmentation for the reduction of examination time is suitable for measuring heart volumes and functional parameters of patients expected to have a nearly normal ejection fraction, whereas for patients with markedly reduced cardiac function further technical improvements of segmented techniques are necessary.

Adult↗

PubMed1996

"Black blood" T2-weighted inversion-recovery MR imaging of the heart.

PURPOSE: To develop a short-inversion-time inversion-recovery (STIR) magnetic resonance imaging pulse sequence for evaluating the myocardium that is relatively free of flow and motion artifact. MATERIALS AND METHODS: The authors implemented a breath-hold, cardiac-triggered STIR sequence with preparatory radio-frequency pulses to eliminate signal from flowing blood. A segmented rapid acquisition with relaxation enhancement (turbo spin echo) readout was used, with the inversion-recovery delay adjusted to null fat. The sequence was implemented at 1.0 and 1.5 T and tested in phantoms, five healthy volunteers, and three patients. RESULTS: Phantom studies confirmed the expected behavior of the sequence. In the volunteers, fat-suppressed images of the heart with STIR contrast were generated in a breath-hold period. Blood in the heart chambers was uniformly nulled, and motion artifacts were effectively suppressed. Focal high signal intensity consistent with edema was seen in two patients with acute myocardial infarction; in a third patient, a paracardiac mass was visualized and sharply demarcated relative to normal myocardium. CONCLUSION: Fast STIR imaging of the heart with effective suppression of flow and motion artifacts was implemented. The approach has much potential for high-contrast imaging in a variety of diseases affecting the heart and mediastinum.

Adult↗

PubMed1996

Coronary arteries: three-dimensional MR imaging with retrospective respiratory gating.

Thin-section, three-dimensional (3D) gradient-echo magnetic resonance imaging of the coronary arteries was performed without and with retrospective respiratory gating in 12 healthy volunteers and one patient. In all examinations, results were improved with gating. In five of seven volunteer examinations, coronary artery delineation on images reconstructed by using the least-squares method for motion detection with navigator echoes was found to be equal to that obtained by using edge detection. Images in five other volunteers covered the entire heart with multiple overlapping 3D slabs. The arteries were segmented from the background and could be viewed from any orientation. The lengths of contiguously visible vessels were as follows: left main coronary artery, 11.5 mm +/- 0.4 (mean +/- standard deviation); left anterior descending branch, 115.9 mm +/- 19.7; left circumflex branch, 97.2 mm +/- 12.5; and right coronary artery, 125.9 mm +/- 18.8. This respiratory gating technique clearly improved depiction of the coronary arteries.

Adult↗

PubMed1996

[Gadolinium-enhanced magnetic resonance angiography with ultra-short echo times. Initial experiences].

Magnetic resonance angiography (MRA) using three-dimensional (3D) gradient-echo sequences with ultra-short echotimes (USTE; 2 ms) and luminal enhancement of vessels with a gadolinium bolus affords the depiction of extended vascular territories with high spatial resolution within 20-60 s. Because of the ultra-short echo and repetition times, filling of the vascular lumen with gadolinium is depicted; the latter is relatively independent of the complex flow effects on which conventional MRA is based. MRA typical flow voids caused by turbulence or slow flow are thus significantly reduced and allow more reliable depiction of stenoses. After implementing the sequences on our scanner, we evaluated the potential of USTE-MRA for the delineation of various vascular territories in 56 patients. A total of 70 vascular territories were depicted and evaluated by two independent radiologists for image quality and obscuring the arteries because of the contrast of veins. Out of the 56 (4%) diagnostic angiographic quality could not be obtained in only 2 cases. In 13 patients (23%) the studies were judged suboptimal, but diagnostic. In only 3 cases (5%) was venous filling judged to obscure the arteries completely on MIPs (maximum intensity reconstructions), although the studies were diagnostic when evaluated with MRPs (multiplanar reconstructions). Venous superimposition occurred significantly more frequently in the neck than else-where. The greatest improvement over conventional MRA was obtained in the abdomen and thorax where USTE-MRAs can be obtained within a breath-hold without motional artifact.

Adolescent↗

PubMed1995

Time-of-flight MR angiography of the brain: comparison of acquisition techniques in healthy volunteers.

OBJECTIVE: The saturation phenomenon that limits vessel visibility in unenhanced time-of-flight MR angiograms can be overcome by the injection of MR contrast agents that shorten the T1 of the blood. Unlike the situation with unenhanced MR angiographic acquisitions, in which the MR parameters must be carefully adjusted to reduce saturation effects, optimization procedures for contrast-enhanced MR angiography focus on the acquired shortening of the T1 of the blood and the time evolution of the T1 over the entire measurement. To improve the quality of contrast-enhanced time-of-flight MR angiographic acquisitions in the brain, we compared different acquisition techniques that exploit shortening of the T1 of the blood. SUBJECTS AND METHODS: High-resolution MR angiographic examinations were done with a 1-T MR system for 12 healthy volunteers. Doses of 0.1 and 0.2 mmol of gadopentetate dimeglumine per kilogram of body weight were injected on two separate days to allow for identical timing of the comparative studies after contrast material injection. The effects of dose of contrast material, MR parameters (TR and flip angle), method of injecting the contrast material (monophasic, biphasic, or continuous slow injection), and K-space acquisition schemes (regular schemes versus collecting the central K-space lines near the beginning or the end of the acquisition) were studied. RESULTS: Higher doses provided better MR angiograms. The flip angle and the TR had to be adjusted on the basis of the Ernst equation and therefore depended on an estimation of the averaged T1 value over the entire measurement. Comparison of the different K-space acquisition schemes confirmed that the evolution of the T1 of the blood over the entire measurement time is important, especially for longer measurements. There was no noticeable difference between the MR angiograms acquired with monophasic or biphasic injections. These injection schemes provided more detailed MR angiograms than did continuous slow injection over the entire measurement. CONCLUSION: Our results show that the quality of contrast-enhanced MR angiograms can be remarkably increased when acquisition techniques that exploit the short T1 of the blood are used.

Adult↗

PubMed1994

Signal targeting with alternating radiofrequency (STAR) sequences: application to MR angiography.

We describe a time of flight subtraction method for cine MR angiography that provides nearly perfect suppression of background signal intensity with excellent flow contrast. The method consists of a preparation phase, during which the longitudinal magnetization of the target tissue is inverted on alternate acquisitions and the background tissue is presaturated, followed by a readout phase using a cine segmented turboFLASH sequence with a shared echo modification to improve temporal resolution. With appropriate alternation of the phases of the radiofrequency excitation pulses, there is cancellation of the background signal intensity but flow signal is optimized. By using a thick section (up to 25 mm), substantial portions of the vascular territory are encompassed in a single plane. This permits rapid, dynamic assessment of flow patterns in areas such as the circle of Willis, carotid bifurcation, or renal arteries. Applications of the method for bright and dark blood cine MR angiography are demonstrated.

Aorta, Abdominal↗

PubMed1994

High speed bolus tagging: time resolved velocity quantification of pulsatile flow in a single breath hold.

We have implemented a high speed method for cardiac-triggered blood velocity quantification within a single breath hold on a conventional MR system. The method, based on bolus tagging, was tested using a pulsatile flow phantom and evaluated in vivo. The image acquisition time was reduced by a factor of N by acquiring N phase encode lines per bolus tag application. The clarity of the flow tag was found to vary with how k-space was covered during data collection. The technique was optimized and multiple bolus tag images were obtained throughout the cardiac cycle within a single breathold.

Aorta, Thoracic↗