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W Luboldt

Publications and source records attributed to W Luboldt.

At least 37 records · Page 2Linked to original sources
PubMed1999

Virtual colonography.

Cross-sectional imaging techniques are increasingly being considered as alternative imaging modalities for colorectal screening. While CT-colonography uses air to insufflate the colon, an enema containing small amounts of paramagnetic contrast represents the basis for MR-colonography. Both techniques provide large three-dimensional data sets of the abdomen, containing the entire colon. Using sophisticated post-processing, the colon can be assessed in any desirable plane from various viewpoints. Thus even virtual endoscopic views can be rendered to assess the inside of the colon. This chapter briefly describes the technical aspects underlying both CT- and MR-colonography. Advantages and disadvantages of the two techniques are critically discussed, comparing them with one another as well as with conventional colonoscopy and barium enema.

Colonoscopy↗
PubMed1999

Influence of helical CT parameters on spatial resolution in CT angiography performed with a subsecond scanner.

RATIONALE AND OBJECTIVES: In helical CT, the beam collimation, table feed (TF) per tube rotation, voltage, current, reconstruction increment, kernel, linear interpolation algorithm (LIA), and contrast are variable parameters. The purpose of this study was to determine which of these parameters are most important to minimize partial volume effects for improving spatial resolution in CT angiography. METHODS: Phantom vessel stenoses of different lengths (2, 8 mm) and diameters (0.5, 1, 2, 3, 4 mm) were scanned with helical CT using a constant tube rotation time of 0.75 sec and 42 selected combinations of the above-mentioned parameters. Orthogonal targeted maximum intensity projections of the stenoses were ordered according to the increase in blurring and noise in a consensus reading by two radiologists blinded to the parameters used. RESULTS: Three millimeters of collimation and TF in conjunction with a 180 degrees LIA and > 250 Hounsfield unit contrast density was considered the optimal parameter combination and enabled a continuous visualization of the stenoses down to 0.5 mm in diameter. A collimation of 1 or 2 mm and 5 mm was considered inferior to a collimation of 3 mm because of, respectively, noise and blurring. With 3 mm collimation, significant blurring occurred when a pitch larger than 1.5 was used. A 3 mm collimation with a pitch of 2 (6 mm TF) was found to be superior to a collimation of 5 mm in conjunction with a pitch of 1 (5 mm TF). With 5 mm collimation, the short stenoses could be visualized only when using a 180 degrees LIA and a TF per tube rotation smaller than 7 mm. Eight and 10 mm collimations failed to depict the short stenoses. CONCLUSIONS: Collimation had the most influence on image quality in CT angiography, followed by LIA, pitch, and contrast density. Decreasing the reconstruction increment to less than one third of the TF or increasing the voltage or current beyond standard values did not improve the delineation of the stenoses. For screening examinations, the authors recommend the use of 3 mm collimation, 180 degrees LIA, and a pitch of 2.

Angiography↗
PubMed1999

Effective contrast use in CT angiography and dual-phase hepatic CT performed with a subsecond scanner.

OBJECTIVE: To deduce an optimal injection protocol for CT angiography and fast dual-phase hepatic CT. METHODS: Fifty-two patients underwent fast dual-phase hepatic CT using one of three different injection protocols: A (0.9 g/sec iodine injection rate, 36 g dose); B (1.35 g/sec, 30 g); C (1.6 g/sec, 40 g). Aortic attenuation time curves as well as aorta-to-liver contrast and hepatic enhancement time curves obtained by region of interest measurements along the helical axis were analyzed. RESULTS: Protocol C revealed a significantly higher peak in aortic attenuation and hepatic enhancement than the other protocols. Approximately 50 seconds after the bolus injection, hepatic enhancement declined to a plateau similar to that seen with the other protocols. In terms of the areas under the curves of the aorta-to-liver contrast and hepatic enhancement dynamics, protocol C was significantly superior to the other protocols. CONCLUSIONS: A high iodine injection rate realized by a high iodine concentration in conjunction with fast dual-phase scanning (total scan time < 50 seconds) promises to enhance CT angiography and contrast of liver lesions.

Angiography↗
PubMed1999

MR colonography: optimized enema composition.

Manganese chloride, iron glycerophosphate, and cellulose additive were assessed as base materials for use in a T1-shortening single contrast enema for magnetic resonance (MR) colonography. Contrast-to-noise ratios (CNRs) were compared to those with the standard 10 mmol/L gadolinium-based enema. On T1-weighted three-dimensional gradient-recalled-echo images, CNRs with the iron glycerophosphate enema exceeded those with the manganese- and gadolinium-based enemas. Use of an additive of 0.8% wt/wt cellulose was found to be practicable as it increased viscosity sufficiently without altering CNR. The gadolinium-based enema can be replaced with an iron glycerophosphate enema to render MR colonography less costly.

Adult↗
PubMed1998

Hybrid rendering of the cervico-cranial arteries using spiral computed tomography.

PURPOSE: The purpose of this study was to develop a shaded-surface and volume display (hybrid rendering method) of the whole vascular system of the cervico-cranial arteries using spiral computed tomography (SCT). MATERIALS AND METHODS: We examined 12 patients with anatomic abnormalities and pathological conditions of the arterial vascular system. The cervico-cranial arteries were segmented using an interactive threshold interval density volume-growing method and visualized with a color-coded shaded-surface display (SSD) rendering method. The adjacent bone structures were visualized using a transparent volume rendering method. RESULTS: In all cases, the entire volume of the vascular system of the cervico-cranial arteries and the anatomic abnormalities and pathological conditions could be visualized. CONCLUSION: Hybrid rendering of the circulation of the cervico-cranial arteries using image data sets from a subsecond spiral CT scanner is useful for the visualization of anatomical and pathological abnormalities and offer a promising minimally invasive alternative compared with other diagnostic procedures.

Adult↗
PubMed1998

Detection of mass lesions with MR colonography: preliminary report.

PURPOSE: To evaluate the performance of magnetic resonance (MR) colonography in the detection of colorectal mass lesions. MATERIALS AND METHODS: Twenty-three patients underwent MR colonography preceding colonoscopy. The colon was filled with a gadolinium-water mixture (1:100) with MR imaging guidance, and the patient was imaged prone and supine with a breath-hold three-dimensional spoiled gradient-recalled sequence. In addition, two-dimensional spoiled gradient-recalled images were acquired before and after intravenous administration of gadopentetate dimeglumine. Images were interactively analyzed on the basis of multiplanar reconstruction by two radiologists. For regions that were not conclusively assessable with multiplanar reconstruction, virtual intraluminal endoscopic images of the colon were reconstructed. MR findings were correlated with colonoscopic results. RESULTS: Two patients were excluded from the analysis. Findings in eight of 11 patients were correctly assessed as normal and in six of 10 as mass-positive. In the four patients with false-negative findings, one had two 8-mm polyps and the other three had polyps smaller than 5 mm. All nine mass lesions larger than 10 mm, as well as four of the 10 polyps ranging between 5 and 10 mm, were detected, but all polyps smaller than 5 mm were missed. In contrast to the polyps less than 5 mm, the four missed polyps (5-10 mm) could be identified retrospectively on virtual intraluminal endoscopic images. Contrast enhancement was documented in 13 polyps. CONCLUSION: Three-dimensional MR colonography provided virtual colonoscopic viewing and helped detection of colonic polyps.

Adult↗
PubMed1997

Preliminary assessment of three-dimensional magnetic resonance imaging for various colonic disorders.

BACKGROUND: Improvements in magnetic resonance imaging (MRI) technology have enabled the acquisition of three-dimensional MRI datasets in a single breath hold. We adopted this technique to make a three dimensional intraluminal and extraluminal assessment of the colon in three patients with various colonic disorders. METHODS: One patient was studied after having a double-contrast barium enema. Two patients had MRI scans after colonoscopy, which showed three colonic tumours in one and multiple polyps in the ascending colon of the other. The process of rectal filling with 1.5-2.0 L water mixed with 15-20 mL 0.5 mol/L gadolinium-diethylenetriaminepentaacetic acid (Gd-DTPA) was monitored with MR fluoroscopic sequence. Three-dimensional datasets of the contrast-filled colon were taken with patients in prone (before and after intravenous administration of 0.1 mmol/kg bodyweight Gd-DTPA) and supine positions. 64 sections with a voxel-resolution of 2.0 x 2.0 x 1.25 mm3-were taken during a 28 s breath hold. Three-dimensional maximum intensity projection, multiplanar reconstruction, and virtual colonoscopic images of the colon were created from these. FINDINGS: Analysis of the coronal source images in conjunction with multiplanar reconstructions revealed all relevant abnormalities, including diverticula, carcinomas, and polyps. Three dimensional maximum-intensity projections gave a morphological overview of the whole colon. Targeted projections, made up of a limited number of coronal source images, showed diverticula and smaller polyps more clearly. After patients were given intravenous contrast all colonic mass lesions were enhanced. Datasets obtained in prone patients gave the best intraluminal views of the colon. Virtual magnetic resonance colonoscopy showed colonic haustra as well as the ileocaecal valve, but did not show clearly the diverticula. All intraluminal mass lesions, on the other hand, were easy to see. INTERPRETATION: The potential of three-dimensional colonic MRI to provide accurate, minimally invasive, cost-effective polyp screening, as well as comprehensive colonic tumour staging, warrants further investigation.

Aged↗
PubMed1997

[CT subtraction angiography (CTSA). Results with an automated "elastic" subtraction algorithm].

PURPOSE: To develop and implement a method to obtain digital subtraction (DS) spiral computed tomography angiograms (SCTA) in order to avoid superimposition of bony structures and vascular calcifications on SCTA maximum intensity projections (MIPs) and shaded surface display (SSD). METHOD: Two SCTA data sets, one before and one during the injection of a contrast agent bolus, were obtained with identical scan parameters. Since ordinary subtraction of the two data sets fails to reliably separate bones and calcifications from the vascular lumen because of motion, a so-called elastic subtraction procedure was designed to correct 3D misregistration between the two data sets. It automatically accommodates for local position changes between baseline and contrast images, including regionally inconsistent non-linear displacements and arbitrary rotations. This method was tested in seven patients and evaluated against ordinary DS in terms of image quality and artifacts. RESULTS: In all patients "elastic" CTSA proved superior to ordinary DS. It provides automated and reliable separation of vessels from bones and calcifications. This improves the delineation of vessels in the neck and the skull base and of intracranial vessels. DS-SCTA facilitates MIPs and SSD without artifacts introduced by thresholding. CONCLUSION: Elastic DS-SCTA is a robust method for automated unmasking of vessels from bones and warrants clinical trials and comparison with MR- and conventional angiography.

Algorithms↗
PubMed1997

[3D MRI of the colon: methods and initial results].

PURPOSE: "Exoscopic" and endoscopic identification of colorectal pathologies via MRI. METHODS: 5 patients (36-88 years), two normal and three with different colorectal pathologies (diverticular disease, polyps and carcinoma of the colon), were examined by MRI after colonoscopy. Subsequent to filling of the colon with a gadolinium-water mixture under MRI-monitoring, 3D-data sets of the colon were acquired in prone and supine positions over a 28 sec breath hold interval. Subsequently multiplanar T1-weighted 2D-sequences were acquired before and following i. v. administration of Gd-DTPA (0.1 mmol/kg BW). All imaging was performed in the coronal orientation. The 3D-data were interactively analysed based on various displays: maximum intensity projection (MIP), surface shadowed display (SSD), multiplanar reconstruction (MPR), virtual colonoscopy (VC). RESULTS: All of the colorectal pathologies could be interactively diagnosed by MPR. On MIP images some pathologies were missed. VC presented the morphology of colon haustra as well as of all endoluminally growing lesions in a manner similar to endoscopy. The colon masses showed uptake of contrast media and could thus be differentiated from air or faeces. CONCLUSION: The potential of CMRI in colorectal diagnosis warrants further investigation in a larger series of patients.

Aged↗
PubMed1997

Attenuation characteristics and application of gadolinium-DTPA in fast helical computed tomography.

RATIONALE AND OBJECTIVES: The computed tomography (CT) attenuation characteristics of gadolinium (Gd)-DTPA have been analyzed both in vitro and in vivo to evaluate the possibility of its substitution for iodine in patients with contraindications for iodine utilization. METHODS: In vitro attenuation values of Gd-DTPA were measured relative to those of iodine under variation of concentration, voltage, preattenuation, and beam hardening. In vivo iodine attenuation values were obtained for different injection rates (3.0 mL/second and 4.5 mL/second) to calculate the attenuation values of 0.5 molar Gd-DTPA to be expected in vivo by the help of the previously obtained attenuation-concentration curves. Subsequently, CT enhancement after an injection of 0.3 mmol/kg body weight Gd-DTPA was evaluated in five patients with contraindications for iodine administration. RESULTS: The injection of a 0.7 molar Gd-DTPA solution at a flow rate of 4.5 mL/second was calculated to be equivalent to that of 2.36 molar iodine at a flow rate of 3 mL/ second. Sufficient enhancement for diagnosis of dissections/ aneurysms of arterial vessels could be achieved. Both arterial and venous cervical or thoracic vessels could be enhanced to 100 Hounsfield units with a bolus injection. In contrast to the thyroid gland, the parenchyma of the liver and the kidney was not sufficiently enhanced. CONCLUSIONS: Gadolinium-DTPA is more effective than iodine in x-ray attenuation; however, its present concentration of 0.5 molar and permitted dose of 0.3 mmol/kg body weight are insufficient to provide parenchymal enhancement with CT. The visualization of arterial vessels appears possible with gadolinium enhanced CT but requires optimal timing and fast scanning capabilities.

Aortic Dissection↗
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↗
PubMed1993

Reaction scheme for the glutamate-ergic, quisqualate type, completely desensitizing channels on crayfish muscle.

In analogy with a recently developed reaction scheme for a channel activated by acetylcholine (ACh; nicotinic), we propose a cyclical reaction scheme which agrees with all data published on the completely desensitizing channel type activated by glutamate (Glu) in crayfish muscle. For every high Glu concentrations, desensitization is mainly from the open state, while at lower Glu concentrations desensitization from the singly Glu liganded closed state contributes significantly. The latter pathway and the high Glu affinity of the desensitized channel states account for complete steady-state desensitization of the channel by Glu concentrations which occur without any channel opening.

Animals↗
PubMed1991

Fc receptor blocking antibodies after active immunization for the treatment of recurrent spontaneous abortion.

In a prospective study 140 couples who had at least three spontaneous abortions (RSA) were studied for the presence of Fc receptor blocking antibodies detected by the erythrocyte antibody rosette inhibition (EAI) assay, for anti-paternal cytotoxic antibodies (APCA), and for mixed lymphocyte culture inhibiting (MLCI) antibodies before and after active immunization with paternal lymphocytes. The comparative analysis revealed the EAI assay to possess a higher sensitivity than the APCA and/or MLCI tests in monitoring the specific immune response after active immunization. The success of pregnancy in EAI positive post-immunization patients was not influenced by the presence or absence of APCA or MLCI. In the light of a successful pregnancy outcome of 85.7% (n = 37) in this study we conclude that the monitoring of Fc receptor blocking antibodies is useful in active immunization protocols for RSA patients.

Abortion, Habitual↗
PubMed1991

[Plateletpheresis with the new cell separator A 201 (Baxter)].

This report deals with our first experiences in testing the new system A 201 (Baxter Fenwal Division) for plateletpheresis in routine application. The apparatus developed from the well-known plasmapheresis equipment Autopheresis C only requires a single venipuncture and uses two separation devices. The platelet cell device produces a primary platelet concentrate. After the donor's disconnection, the platelet-containing plasma is separated into 400 ml of red cell and leucocyte-free plasma and the platelet concentrate, which is done by a rotating membrane filter of the same instrument. Plateletpheresis was performed on 34 healthy donors (26 male and 8 female), formerly experienced by other apheresis procedures. Different samples were drawn from the donors before, during and after apheresis. In comparison with other apheresis procedures there were no significant differences in the harvested platelets (3 +/- 0.7 x 10(11), but the preparations showed a higher contamination of leucocytes (3.7 +/- 3.7 x 10(8). This means a considerable disadvantage and requires improvement. Yet the advantages of this separator are obvious: Reduction of needed anticoagulation to only 6% of processed blood volume, single needle technique, safety of operation and, due to less size, more mobility.

Blood Donors↗
PubMed1991

[Thrombocytapheresis with the (Baxter) A 201 cell separator--initial data of biocompatibility].

The cell separator A 201 was a new platelet pheresis prototype designed to carry out a discontinuous apheresis while platelet-rich plasma (PRP) is sampled continuously. After donation, a platelet concentrate (PC) and a fresh frozen plasma was collected from the PRP by the plasma cell-C device. The PC contained 2.6 +/- 0.7 x 10(11) platelets with a leucocyte contamination of 3.9 +/- 3.9 x 10(8) and an erythrocyte contamination of 3.0 +/- 3.0 x 10(8). The fresh frozen plasma was nearly cell-free. Prior, during and after apheresis we analysed hemolysis and coagulation parameters. There was no evidence for hemolysis. The analysis of the coagulation factors and of the Thrombin-Antithrombin III-complex, however, gave a hint of an activation of coagulation.

Biocompatible Materials↗