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G Laub

Publications and source records attributed to G Laub.

At least 73 records · Page 4Linked to original sources
PubMed1994

Improved MR angiography: magnetization transfer suppression with variable flip angle excitation and increased resolution.

Results at conventional magnetic resonance (MR) angiography were compared with results at MR imaging with a sequence combining optimized magnetization transfer (MT) saturation and tilted optimized nonsaturating excitation (TONE). Forty images were obtained of five healthy volunteers and five patients with known intracranial vascular abnormalities (four men and six women, aged 22-72 years). Four blinded readers found improved vessel penetration, enhanced vessel-to-background contrast, the better vessel detail in the MT saturation-TONE images than in the conventional three-dimensional time-of-flight MR angiograms.

Adult↗
PubMed1994

[Basic principles of MR angiography. An introduction].

Contrast MR imaging is based on the physical properties of biological tissues, such as relaxation times T1 and T2 and proton density. On particular, however, the motion of protons will affect image quality in MRI, resulting in severe image artifacts. There are two types of flow phenomens, referred to as time-of-flight (TOF) and phase effects. In the past several techniques have been developed in order to eliminate or compensate for any artifacts related to the flow effects. On the other hand, it is also possible to make use of flow effects for the purpose of flow visualization. These techniques are commonly referred to as MR angiography. Depending on the flow effect used, there are two types of MR angiography techniques currently available: TOF and phase contrast MR angiography. Each of the techniques makes use of one effect and suppresses the other one as much as possible. The purpose of this paper is to review the underlying physical principles of MR angiography and to show the clinical applications for it.

Algorithms↗
PubMed1992

Magnetic resonance angiography of intracranial aneurysms: comparison with intra-arterial digital subtraction angiography.

Magnetic resonance angiography (MRA) with flow rephased gradient-echo sequences is a new non-invasive method for vascular imaging. We compared MRA and intra-arterial digital subtraction angiography in 18 patients with intracranial aneurysms to test whether MRA presently provides an alternative to cerebral angiography for the diagnosis of these anomalies. MRA showed 19 of the 22 aneurysms detected (86.4%). However, problems, especially with turbulent or slow flow, resulted in 6 studies (27.3%) with limited and 2 with questionable demonstration of an aneurysm, and 1 false negative study. At present, MRA is definitely inferior to angiography for the demonstration of intracranial aneurysms, due to its lower resolution and other limitations.

Adult↗
PubMed1991

Improvement of 3D acquisition and visualization in MRI.

Three-dimensional (3D) visualization techniques are becoming an ever more important aid in the interpretation of tomographic data. Up to now, however, they have not received widespread use in MRI, because both acquisition and visualization techniques have been inadequate. In this paper we describe new 3D acquisition techniques which can acquire up to 128 slices with a resolution of 256 x 256 pixels in from 8 to 20 min. These techniques produce 3D data sets with excellent contrast and few motion artifacts, which are very well suited for 3D visualization techniques. For the visualization we investigate several rendering techniques, describe some improvements and compare their results. We found that there is no single method which renders all objects equally well. We show which shading method is best suited for different objects and why the other methods fail. Our studies suggest that in a 3D view with several objects each object should be rendered with a separate shading method. In so doing, 3D views can be generated which look like the real human anatomy.

Data Display↗
PubMed1991

[MR angiography of the abdominal aorta: initial experience].

Flowing blood can be demonstrated as bright signal in MR-imaging resulting in MR-angiography (MRA). This study presents the results of MRA using the "time of flight"-effect in which projection angiograms along the longitudinal axis were established by a row of 2D-gradient echo (GE) images (FLASH) in breath-hold technique. The method was proven in 5 normal volunteers and evaluated against DSA in 21 patients with aortic diseases. The preliminary results demonstrate a satisfactory flow signal in the normally perfused aorta; thus occlusions, stenoses, and aneurysms could be defined clearly. In smaller vessels the signal was still insufficient. Diagnostic problems of vascular overlapping can be solved in most cases by rotating the angiograms, and by additional analysis of individual 2D-GE images. In the present form the quality of MRA is still inferior to that of DSA.

Angiography, Digital Subtraction↗
PubMed1991

Three-dimensional time-of-flight MR angiography: applications in the abdomen and thorax.

The application of three-dimensional (3D) time-of-flight (TOF) magnetic resonance (MR) angiographic techniques to the vasculature of the abdomen and thorax has not, to the authors' knowledge, been previously reported; this is possibly due to the large amount of physiologic motion in these regions along with the anticipated sensitivity of the 3D acquisition scheme to image degradation caused by motion artifact. The authors describe an asymmetric short-echo velocity-compensated 3D TOF technique that minimized the effects of physiologic motion on image quality and provided rapid high-resolution 3D MR arteriograms of the abdomen and thorax. Contiguous 3D volumes were often combined to provide sufficient anatomic coverage. Benefits include high spatial resolution and minimization of signal loss; limitations include sensitivity to motion artifact and progressive spin saturation.

Abdomen↗
PubMed1991

[MR angiography of the abdominal veins].

On the basis of the time-of-flight effect in 18 normal volunteers and 119 patients with different diseases of the abdominal veins (inferior vena cava, porto-splenic system, renal/hepatic/iliac veins) magnetic resonance (MR) angiograms were compared with the DSA, CT and US results. The MR technique included a series of 2D gradient-echo (Flash) images in which the patients held their breath and projection angiograms (PA) (MIP algorithm). PA of the inferior vena cava and renal veins had a sensitivity of 90% and a specificity of 88.8%. The results demonstrate that in all cases diseases of the large veins could be detected using all the MR information available. It is suggested that this method is so far not satisfactory in the evaluation of small vessels and slow intravascular flow conditions.

Abdomen↗
PubMed1990

Displays for MR angiography.

There are several MR imaging procedures that result in three-dimensional data of moving spins. One way to evaluate these data is a sequential observation of 2D slices. A more common and efficient approach is to retrospectively calculate two-dimensional projection images at different angles representing individual views of the tomographic volume. The display of different views from the same data set will allow a realistic visualization of the blood vessel anatomy.

Algorithms↗
PubMed1990

[A new method of 3-dimensional reconstruction of the head and neck].

In the past decades the development of MRI has significantly increased the importance of diagnostic imaging of head and neck lesions. The standard imaging method is based on two-dimensional slices. The present study was performed to evaluate the diagnostic value of 3D MRI-reconstructions for head and neck lesions. The 3D reconstruction method and the results of the 3D-reconstructed images are presented. Important aspects of the interesting structures can be evaluated much more easily with reconstructed images than by mentally reconstructing two-dimensional slices. In the light of the present results, 3D reconstruction promises to be an accurate method for the diagnosis of head and neck lesions and might be of clinical importance in the future.

Computer Simulation↗
PubMed1990

[The value of 3D proton spin tomography reconstruction as exemplified by an extensive parotid adenoma].

In the past few years, 3 D reconstruction has been established as a new imaging method in various medical fields, such as orthopedic surgery and neurosurgery. In a former article, the authors introduced a new 3 D imaging method for the head and neck. The present study reports the case of a 37-year-old woman with a huge adenoma of the parotid gland. The tumor grew along the skull base, protruding onto the left tonsil. The diagnostic value of the authors' reconstruction method for lesions in the head and neck is discussed. The results indicate that this technique might be of significant clinical importance for special questions arising in the head and neck region as well as for preoperative planning in the case of certain tumors.

Adenoma↗
PubMed1990

[The further development of the 3D-MRI reconstruction technic for the head-neck area].

Twenty-one healthy volunteers and seventeen patients with head and neck lesions were examined with 3D MR imaging since the end of 1988. A new kind of reconstruction mode was used, which shows the structures of the region of interest by overlaying a predetermined window within the three-dimensional reconstruction of the head. Using this mode, the morphology of the lesion could be evaluated more precisely than by using individual two-dimensional slices. With regard to preoperative surgery planning, the previous results were insufficient. With the new development and increased capacity of the MRI-technique and improvement of the reconstruction mode it is now possible to "cut" several slices in different orientations into the head achieving higher resolution of the images. The innovation of the method and its actual clinical value is discussed in the example of a meningioma of the sphenoid which has been examined by both reconstruction modes.

Head↗
PubMed1990

[3D-MRT-reconstructions of space-occupying lesions in the head and neck regions].

3-D reconstructions in the head and neck were carried out on 21 normals and 11 patients with space-occupying lesions, both before and after the administration of Gd-DTPA. The 3-D reconstructions were obtained by the "ray-tracing" method. For the 3-D reconstructions, portions of the skull surface image were removed to permit views of the deeper tissues. The 3-D reconstructions included an hypoglossus neurinoma, a glomus tumour, two carcinomas of the maxillary antra, three naso-pharyngeal carcinomas, a parotid adenoma, an oro-pharyngeal haemangioma and two lesions in the neck. The 3-D reconstructions provided a better understanding of the morphology than was obtained from the two-dimensional images. 3-D reconstructions of lesions in the head and neck will become a valuable diagnostic method for demonstrating space-occupying lesions, particularly with regard to surgical planning.

Adenoma↗
PubMed1990

Magnetic resonance angiography.

Magnetic resonance imaging allows the visualization of vascular structures without the use of contrast agents. With three-dimensional imaging techniques, based on gradient echo sequences, up to 128 slices can be acquired within a maximum acquisition time of 21 minutes at a spatial resolution of approximately 1 mm. This allows the carotid arteries and major intracerebral vascular structures to be displayed. From the primary three-dimensional data set, projective images at arbitrary projection angles can be calculated. This technique is extremely helpful for assigning spatially complex vascular structures and identifying vascular disease. As a result of rapid technologic advances in magnetic resonance angiography, it is now necessary to assess its clinical utility for identifying atherosclerotic stenoses, aneurysms, and arteriovenous malformations. Limited experience to date has shown that magnetic resonance angiography, because of its high sensitivity to these vascular diseases, may play a clinically important role as a screening method.

Contrast Media↗
PubMed1989

[A simplified technic in high-resolution MR tomography of the shoulder: ZEPRA (Zoom of Eccentric Positioned Regions by active Aliasing)].

A fairly easy method for high-resolution MR imaging of the shoulder is described. The combination of a defined arrangement of the gradients with a small-volume Helmholtz coil provides the possibility of a high zoom of structures apart from the magnet's centre. The maximal achievable zoom factor depends on the ratio of FOV/sensitive coil volume. The ZEPRA method acts by phase-encoded aliasing only. With this technique all interesting soft tissue of the shoulder may readily be visualized in every direction and with every type of sequence.

Humans↗
PubMed1989

Clinical evaluation of a motion compensated double echo sequence in MRI of the brain.

This study is a clinical evaluation on 5 volunteers and 20 patients of an improved sequence using rephasing gradients for motion compensation, applied to MR imaging of the brain at 1.5 T. The sequence is a double spin echo sequence with a normal first echo at TE = 15 ms and a second echo at TE = 90 ms with first and second order motion compensation in the readout gradient direction; the band width of the second echo is halved for improved S/N. Results demonstrate a dramatic improvement in image quality. Vascular and CSF flow are rephased, ghosting is reduced and signal voids no longer exist. Most remarkable is the substantial suppression of artifacts from voluntary movements such as from swallowing or rotation of the eyes. ECG triggering does not further improve image quality and is thus no longer needed.

Brain↗
PubMed1989

Three-dimensional (volume) gradient-echo imaging of the carotid bifurcation: preliminary clinical experience.

This study was designed to test the accuracy of magnetic resonance (MR) imaging with a FLASH (fast low-angle shot) 40 degrees volume pulse sequence by comparing it with intraarterial digital subtraction angiography (DSA) in patients with suspected carotid artery stenoses. Fifteen patients referred for evaluation of anterior circulation in cerebrovascular disease composed the pilot group. Twelve patients underwent correlative intraarterial DSA examinations. The FLASH volume sequence, with an echo time of 7.7 seconds, produced high-signal-intensity vascular images for 28 of 30 bifurcations. Of the 24 carotid bifurcations studied with DSA, 22 were depicted with MR angiography. Among the depicted bifurcations, 21 showed good correlation with the DSA images. These included four of four normal bifurcations, three of three with mild stenosis, four of four with moderate stenosis, eight of nine with severe stenosis, and two of two with occlusions. With respect to ulceration, three of four MR angiographic studies showed good correlation with DSA images. This preliminary experience indicates that the method is reproducible and capable of delineating carotid lesions in patients and that it can be performed in conjunction with conventional spin-echo imaging of the brain with only a small increase in patient examination time.

Adult↗