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Biomedical subjects

Maximilian Reiser

Publications and source records attributed to Maximilian Reiser.

At least 73 records · Page 4Linked to original sources
PubMed2002

Oxygen-enhanced MRI of the brain.

Blood oxygenation level-dependent (BOLD) contrast MRI is a potential method for a physiological characterization of tissue beyond mere morphological representation. The purpose of this study was to develop evaluation techniques for such examinations using a hyperoxia challenge. Administration of pure oxygen was applied to test these techniques, as pure oxygen can be expected to induce relatively small signal intensity (SI) changes compared to CO(2)-containing gases and thus requires very sensitive evaluation methods. Fourteen volunteers were investigated by alternating between breathing 100% O(2) and normal air, using two different paradigms of administration. Changes ranged from >30% in large veins to 1.71% +/- 0.14% in basal ganglia and 0.82% +/- 0.08% in white matter. To account for a slow physiological response function, a reference for correlation analysis was derived from the venous reaction. An objective method is presented that allows the adaptation of the significance threshold to the complexity of the paradigm used. Reference signal characteristics in representative brain tissue regions were established. As the presented evaluation scheme proved its applicability to small SI changes induced by pure oxygen, it can readily be used for similar experiments with other gases.

Adult↗
PubMed2002

Multidetector computed tomography (MDCT) in coronary surgery: first experiences with a new tool for diagnosis of coronary artery disease.

BACKGROUND: Selective coronary angiography (SCA) is the standard invasive procedure for diagnosis in patients eligible for coronary artery bypass grafting (CABG). A recently developed, highly sensitive multidetector computed tomography (MDCT) scan holds promise to be of almost comparable quality and predictiveness. We examined a blinded series of preoperative patients who were admitted to hospital for conventional and minimally invasive CABG procedures. Patients underwent CT scans in addition to SCA; findings were compared regarding location and degree of coronary artery stenosis. METHODS: Twenty patients underwent electrocardiogram-gated helical CT scanning. Images with 250 ms effective exposure time were reconstructed with retrospective electrocardiogram gating. Location and degree of coronary stenoses were described and compared with findings of SCA. The study was limited to patients with a heart rate of less than 70 beats per minute and who had the ability to hold their breath for 20 to 30 seconds. RESULTS: Coronary arteries were clearly displayed by MDCT. Compared with SCA, sensitivity was 92%, specificity 84%, and negative predicted value 89% for significant stenosis (more than 50%). Early forms of atherosclerotic changes were even clearer on MDCT. In addition, the CT examination allowed differentiation of calcified and fatty or fibrous stenoses. CONCLUSIONS: Multidetector CT scanning is an effective noninvasive technique for the diagnosis of coronary artery disease. In selected patients, MDCT scanning might be able to replace SCA as a preoperative test for CABG procedures. The intrathoracic situs can be clearly exposed as it is important for the planning of minimally invasive CABG procedures.

Coronary Angiography↗
PubMed2002

Quantitative cartilage imaging of the human hind foot: precision and inter-subject variability.

Alterations of ankle cartilage are observed in degenerative and inflammatory joint disease, but cartilage cannot be directly visualized by radiography. The purpose of this study was therefore to analyze the feasibility and precision of quantitative cartilage imaging in the human hind foot (talocrural, talotarsal, and intertarsal joints), and to report the inter-subject variability for cartilage volume, thickness and surface areas. The feet of 16 healthy volunteers were imaged using a 3D gradient-echo magnetic resonance imaging sequence with water-excitation. After interpolation to a resolution of 1 x 0.125 x 0.125 mm3 the cartilage plates were segmented, and the cartilage volume, thickness, and surface areas determined. The precision (four repeated measurements) was examined in eight volunteers, the RMS average CV% being 2.1% to 10.9% in single joint surfaces, and < or = 3% for the cumulative values of all joints. The mean cartilage thickness ranged from 0.57+/-0.08 (navicular surface) to 0.89+/-0.19 mm (trochlear surface for tibia). In conclusion this study shows that it is feasible to quantify thin cartilage layers in the hind foot under in vivo imaging conditions, and that the precision errors are substantially smaller than the inter-subject variability in healthy subjects.

Adult↗
PubMed2002

Diffusion-weighted imaging of the spinal column.

Diffusion-weighted imaging of the musculoskeletal system including the spine is a new MR imaging method. Several studies have shown significantly different diffusivities for various pathologic conditions such as edema and tumor. The specificity of diagnosis may be increased and therapeutic effects may be monitored. Diffusion-weighted sequences especially have been shown to be an additional tool for differentiating vertebral fractures caused by osteoporotic collapse with bone marrow edema and metastatic collapse. Inclusion criteria should include: (1) unknown reason for the vertebral collapse, (2) lack of sclerosis, and (3) no prior therapy. Patients with trauma or treated metastases may exhibit different signal intensities. In general, those patients do not pose problems in differential diagnosis. New sequence developments and higher magnetic field gradients should be able to increase spatial resolution and decrease problems from motion artifacts. Studies with larger patient groups and sequences that quantify the results with ADCs are the necessary next steps.

Aged↗
PubMed2002

Three-dimensional analysis and visualization of regional MR signal intensity distribution of articular cartilage.

The aim of this study was to develop a technique for analyzing and visualizing the regional, three-dimensional signal intensity distribution of articular cartilage in MR images, as a potential surrogate marker of structural or biochemical alterations in early osteoarthritis. Exemplary MR-images of human patellae were acquired at a resolution of 1.5 x 0.31 x 0.31 mm(3), using a gradient-echo sequence with water excitation, and by combining three data sets to secondary images of proton density. After segmentation of the cartilage outlines, these were transferred to the other images. Contiguous slices were automatically divided into sub-regions that extend from the surface to the bone interface (layers) as well as from medial to lateral (sections). The signal intensity was then calculated and projected onto a three-dimensional representation of the articular surface, either by averaging through the depth (sections) or by visualizing the signal intensity at distinct levels in depth (layers). The exemplary data indicate that the reproducibility for regional analyses is in the same range as for the entire patellar cartilage, and that the distribution patterns of proton density delineated with MRI are in agreement with the literature. In conjunction with suitable MR protocols, this post-processing technique has potential to allow for detection and quantification of early degenerative processes in cartilage, before macro-morphological lesions occur.

Adult↗
PubMed2002

Determination of coronary calcium with multi-slice spiral computed tomography: a comparative study with electron-beam CT.

Electron-beam Computed Tomography (EBCT) has been used for years to quantify coronary artery calcification as a marker of coronary atherosclerosis. The aim of this study was to determine the diagnostic accuracy of a new scanner, the Multi-slice Spiral CT (MSCT), for the assessment of coronary calcification and to compare this new technique to EBCT. The study population consisted of 99 male patients, aged 60 +/- 10 years with suspected or known coronary artery disease. With EBCT 40 axial slices, ECG-triggered (scan time = 100 ms, slice thickness = 3 mm), were acquired in one breath-hold (35 +/- 5 s). For MSCT simultaneous acquisition of four axial slices (scan time = 250 ms, slice thickness = 2.5 mm), allowed the entire heart (48 slices) to be covered in one breath-hold of 25 +/- 5 s. For quantification of coronary calcium the Volumetric Calcium Score (VCS) was calculated. There was an excellent correlation for the VCS (r = 0.994, p = 0.01, mean difference = 97 +/- 115) between both scanners. Comparison of low (1-100), moderate (101-400), high (401-1000) and very high score values (>1,000) showed no significant differences. The number of calcified lesions and densities were statistically not different. Mean variability of the two scans was 17%. The MSCT scanner is equivalent to EBCT for the determination and quantification of coronary calcium and can therefore be used for calcium screening. With application of the spiral mode technique further improvement in variability can be expected, thus allowing for follow-up studies to determine progression or regression of atherosclerosis with high accuracy.

Calcinosis↗
PubMed2002

Computed tomography-fluoroscopy guided drainage of pericardial effusions: experience in 11 cases.

RATIONALE AND OBJECTIVES: The purpose of the study was to evaluate feasibility and safety of CT-fluoroscopy in the drainage of pericardial effusion in cases not accessible by sonography. METHODS: Eleven drainages were performed in Seldinger-technique under CT-fluoroscopy on eight patients suffering from pericardial effusion. The inclusion criterion was a sonographically proved pericardial effusion not drainable under sonographic surveillance. In seven procedures the catheter was positioned using a medial, in four procedures a lateral approach from the apex was chosen. RESULTS: All catheters could be placed successfully (11/11) in the pericardial effusion and allowed for draining of the effusion in 10 of 11 cases. One epicardial laceration necessitated a surgical approach. The elapsed total procedure time for the drainage was on average 18:23 +/- 8:58 minutes. CONCLUSIONS: Visual surveillance by CT-fluoroscopy is a feasible method in the drainage of pericardial effusions even in cases not accessible by ultrasound.

Adult↗
PubMed2002

Focal epileptiform activity in the brain: detection with spike-related functional MR imaging--preliminary results.

The purpose of this study was to develop a spike-related functional magnetic resonance (MR) imaging method to detect epileptic brain activity. Correlations between simultaneous spike-related functional MR imaging and electroencephalographic (EEG) recordings were performed in 10 patients with focal epilepsy. Postprocessing techniques were implemented to eliminate contamination of the EEG recording from ballistocardiography and the echo-planar MR imaging sequence. A diagnostic EEG recording was achieved during functional MR imaging. Spike location correlated with the site of blood oxygen level-dependent signal increase. Spike-related functional MR imaging is a promising technique for detecting focal epileptic brain activity.

Adult↗
PubMed2002

Acute osteoporotic and neoplastic vertebral compression fractures: fluid sign at MR imaging.

PURPOSE: To evaluate the occurrence, location, and shape of the fluid sign in acute osteoporotic and neoplastic vertebral compression fractures at magnetic resonance (MR) imaging. MATERIALS AND METHODS: The study group comprised 87 consecutive patients with acute vertebral compression fractures due to osteoporotic (n = 52) or neoplastic (n = 35) infiltration. The MR imaging protocol included nonenhanced T1-weighted spin-echo and short inversion time inversion-recovery sequences and a 1.5-T system. Readers blinded to the outcome documented the occurrence, shape, and location of the fluid sign with consensus. The fluid sign was correlated with the cause, age, and severity of the fracture. The diagnosis was confirmed with surgery, follow-up MR imaging, clinical follow-up, or unequivocal imaging findings. Wilcoxon and chi(2) tests were used to assess significance. RESULTS: In fractured vertebral bodies, the fluid sign was adjacent to the fractured end plates and exhibited signal intensity isointense to that of cerebrospinal fluid. The fluid sign was linear (n = 16), triangular (n = 5), or focal (n = 2) and was significantly associated with osteoporotic fractures (21 [40%] of 52; P <.001). The fluid sign occurred in two (6%) of 35 neoplastic compression fractures. Histologic examination demonstrated osteonecrosis, edema, and fibrosis at the site of the fluid sign. There was a tendency toward older fractures exhibiting the fluid sign, but this relationship was not significant (P >.05). In osteoporotic fractures, the fluid sign was significantly associated with fracture severity (P <.05). CONCLUSION: The fluid sign is featured in acute vertebral compression fractures that show bone marrow edema. It can be an additional sign of osteoporosis and rarely occurs in metastatic fractures.

Aged↗
PubMed2002

Improved quality of life in patients with refractory or recidivant ascites after insertion of transjugular intrahepatic portosystemic shunts.

BACKGROUND: We have recently shown that the transjugular intrahepatic portosystemic shunt (TIPS) is more effective than paracentesis in the treatment of cirrhotic patients with severe ascites and can prolong survival in selected patients. Although an improved quality of life (QOL) has been suggested in these patients after the TIPS procedure, so far there are no data available to substantiate this assumption. Therefore, the aim of this study was to determine the effect of TIPS on the QOL in cirrhotic patients with refractory or recidivant ascites. METHODS: 21 cirrhotic patients who underwent TIPS for refractory or recidivant ascites were investigated. All patients were pretreated with repeated paracentesis for at least 1 year. Before the procedure and at 3 and 6 months during follow-up, the patients themselves rated QOL, fatigue and physical performance on a visual analogue scale (range 0-100). Furthermore, QOL was determined by the QOL index (range 0-10) according to Spitzer. RESULTS: Patients' rating of the QOL on the visual analogue scale significantly increased from 35 +/- 25 (baseline) to 64 +/- 28 (3 months), and 66 +/- 24 (6 months; p = 0.02). Similarly, the QOL index significantly increased from 6.9 +/- 2.0 (baseline) to 8.3 +/- 2.1 (3 months), and 8.6 +/- 1.7 (6 months; p < 0.001). The increase of QOL was more pronounced in patients with complete response to TIPS. CONCLUSIONS: We demonstrate that TIPS for refractory or recidivant ascites improves the QOL in patients with cirrhosis. Our data indicates that this improvement is dependent on the response to therapy.

Ascites↗
PubMed2002

Detection of malignant hepatic lesions before orthotopic liver transplantation: accuracy of ferumoxides-enhanced MR imaging.

OBJECTIVE: The purpose of this study was to evaluate the diagnostic accuracy of ferumoxides-enhanced MR imaging for screening malignant hepatic lesions before orthotopic liver transplantation. MATERIALS AND METHODS: The study comprised 48 patients who underwent MR imaging within 6 months before transplantation. Imaging techniques included unenhanced and ferumoxides-enhanced T1-weighted gradient-echo and T2-weighted fast spin-echo sequences and ferumoxides-enhanced T2(*)-weighted gradient-echo sequences. Qualitative and quantitative analyses were performed; the gold standard was the histopathologic reports of explanted livers. RESULTS: Twenty patients had malignant hepatic lesions, and 24 hepatocellular carcinomas were histopathologically proven. The mean area under the receiver operating characteristic curve and the mean sensitivity were significantly greater for the image sets with ferumoxides-enhanced gradient-echo sequences than for those without these sequences. The mean sensitivity and specificity of all sequences were 85% and 74% on a per-patient basis, respectively. The mean contrast-to-noise ratio was significantly greater for the ferumoxides-enhanced T2(*)-weighted gradient-echo sequences than for any other sequences and for the ferumoxides-enhanced T1-weighted gradient-echo sequences than for unenhanced sequences and the ferumoxides-enhanced T2-weighted fast spin-echo sequences. CONCLUSION: Ferumoxides-enhanced gradient-echo sequences improved the diagnostic accuracy and the sensitivity for detecting malignant hepatic lesions in patients with end-stage cirrhosis of the liver. However, the specificity was not improved even after the administration of ferumoxides because of the false-positive lesions that were mainly the result of fibrotic changes.

Adult↗
PubMed2001

Whole-body computed tomography in polytrauma: techniques and management.

An interdisciplinary team should be involved in the diagnosis and management of severely injured patients. The adoption of criteria for starting treatment for multiple trauma avoids underestimation of seriousness of injury. These criteria are established by the circumstances of the accident, the patterns of trauma, and the vital findings. Basic diagnosis comprises a limited number of plain films in the trauma room, including supine chest, lateral cervical spine, and pelvis, and ultrasound of abdomen, pleura, and pericardium. Organ diagnosis using CT is complementary and depends on the clinical findings and findings from the basic investigations. We recommend spiral CT (skull base 2/2/4 mm, cerebrum 8/8/8 mm native) and after intravenous contrast medium thoracic (5/7.5/5 mm) and abdominal CT (8/12/8 mm). Image reconstruction of bony structures can be added. The CT and the trauma center should be in close proximity; time-consuming transfers must be avoided. If this is not possible, a CT can be integrated in the trauma room. Our hospital trauma registry contains over 2200 entries. A quality committee has been established and external quality control is implemented.

Humans↗
PubMedDate not supplied

A case of an upper gastrointestinal bleeding due to a ruptured dissection of a right aortic arch.

We report a case of severe upper gastrointestinal hemorrhage with a rare underlying cause. The patient was unconscious when he was admitted to the hospital. No chest radiogram was performed. Routine diagnostic measures, including endoscopy, failed to reveal the origin of the bleeding, which was believed to originate from the esophagus secondary to a peptic ulcer or varices. Exploratory laparotomy added no further information, but contrast-enhanced multislice computed tomography (MSCT) of the chest showed dextroposition of the widened aortic arch with a ruptured type-B dissection and a consecutive aorto-esophageal fistula (AEF). The patient died on the day of admission. Noninvasive MSCT angiography gives rapid diagnostic information on patients with occult upper gastrointestinal bleeding and should be considered before more invasive conventional angiography or surgery.

Aortic Dissection↗
PubMedDate not supplied

Fully automated biomedical image segmentation by self-organized model adaptation.

In this paper, we present a fully automated image segmentation method based on an algorithm that provides adaptive plasticity in function approximation problems: the deformable (feature) map (DM) algorithm. The DM approach reduces a class of similar function approximation problems to the explicit supervised one-shot training of a single data set. This is followed by a subsequent, appropriate similarity transformation, which is based on a self-organized deformation of the underlying multidimensional probability distributions. We apply this algorithm to the real-world problem of fully automated voxel-based multispectral image segmentation, employing magnetic resonance data sets of the human brain. In contrast to previous segmentation approaches, the knowledge obtained within the segmentation procedure of a single prototypical reference data set can be re-utilized for the segmentation of new, 'similar' data employing a strategy of incremental adaptive learning based on the DM algorithm. Thus, we obtain a fully automatic segmentation method that does neither require manual contour tracing of training regions, visual classification of voxel clusters, nor any other kind of human intervention. Our application demonstrates that flexible learning by a strategy of self-organized incremental model adaptation can contribute to increase the efficiency and practicability of biomedical image processing systems.

Algorithms↗
PubMedDate not supplied

CT/fluoroscopy-guided transthoracic needle biopsy: sensitivity and complication rate in 98 procedures.

PURPOSE: The purpose of this study was to evaluate CT/fluoroscopy (CTF)-guided core needle biopsies (CNBs) in the thorax. METHOD: Ninety-eight biopsies were performed using a core biopsy needle (18G) with a reusable biopsy gun under CT/F. All results were compared to surgery plus histology or to clinical follow-up of >12 months. Sensitivity, specificity, and negative predictive value (NPV) were calculated. RESULTS: For pulmonary biopsies, sensitivity was 94%, specificity 100%, and NPV 73%; no significant correlation between the pneumothorax rate and the intrathoracic penetration depth was found. For biopsies of the mediastinum and pleura, sensitivities were 87 and 80%, respectively; specificity was 100% in both locations. A pneumothorax occurred in 21%, a pneumothorax requiring drainage in 2.0%. CONCLUSION: CT/F-guided CNB is a reliable method to obtain thoracic biopsies, with a complication rate of 2.0%.

Adult↗