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Dominik Weishaupt

Publications and source records attributed to Dominik Weishaupt.

At least 37 records · Page 2Linked to original sources
PubMed2005

Sensitivity encoding as a means of enhancing the SNR efficiency in steady-state MRI.

Sensitivity encoding (SENSE) with a receiver coil array is typically used as a means of reducing the scan time in MRI. The speed benefit usually comes at some expense in terms of the signal-to-noise ratio (SNR) efficiency, which has been notorious as the main downside of SENSE and parallel MRI in general. In this work it is shown that in steady-state gradient-echo imaging the parallel approach may as well be used to increase the SNR efficiency. The basic idea is to balance reduced phase encoding by increasing the repetition time. In this fashion both the acquisition duty cycle and the steady-state magnetization can be enhanced, resulting in considerable net gains in SNR yield. It is argued that the reduction factor in parallel imaging is essentially an additional degree of freedom in optimizing the SNR. The optimal SENSE factor depends on scan, tissue, and hardware parameters, assuming values up to 3.0 and higher. The achievable SNR benefit also depends on the spoiling regime and is most pronounced for RF-spoiled techniques. The proposed mechanism is demonstrated by simulations and phantom experiments, as well as by contrast-enhanced angiography in vivo, achieving an approximate doubling of the SNR efficiency.

Computer Simulation↗
PubMed2005

MR imaging of the forefoot: Morton neuroma and differential diagnoses.

Magnetic resonance (MR) imaging of Morton neuromas is highly accurate. Morton neuromas are more conspicuous when the patient is prone positioned and the foot is plantar flexed than in the supine position with the toes pointing upward. MR imaging of Morton neuromas has a large influence on the diagnostic thinking and treatment plan of orthopedic foot surgeons. The most common differential diagnoses include intermetatarsal bursitis, stress fractures, and stress reactions. Some diagnoses (nodules associated with rheumatoid arthritis, synovial cyst, soft tissue chondroma, and plantar fibromatosis) are rare and can be diagnosed with histologic correlation only.

Bursitis↗
PubMed2005

Interosseous ligament tears of the wrist: comparison of multi-detector row CT arthrography and MR imaging.

PURPOSE: To compare the accuracy of multi-detector row computed tomographic (CT) arthrography and magnetic resonance (MR) imaging in depicting tears of dorsal, central, and palmar segments of scapholunate (SL) and lunotriquetral (LT) ligaments in cadavers. MATERIALS AND METHODS: Cadaver wrists were obtained and used according to institutional guidelines and with informed consent of donors prior to death. Nine cadaver wrists of eight subjects were evaluated. MR images were obtained with a 1.5-T MR unit. Imaging protocol included intermediate-weighted coronal and transverse fast spin-echo and coronal three-dimensional gradient-echo sequences. Multi-detector row CT arthrography was performed after tricompartmental injection of 3-6 mL of contrast material with a concentration of 160 mg per milliliter of iodine. Palmar, dorsal, and central segments of both ligaments were analyzed on transverse and coronal MR images and multiplanar multi-detector row CT reconstructions by two musculoskeletal radiologists working independently. Open inspection of the wrists was the reference standard. Sensitivity, specificity, accuracy, and positive and negative predictive values were calculated from the imaging and gross pathologic readings. Statistical significance was calculated with the McNemar test. Weighted kappa values for interobserver agreement were calculated for both imaging modalities. RESULTS: All ligament segments could be visualized in all cases with both imaging modalities. CT arthrography was more sensitive (100%) than MR imaging (60%) in detection of palmar segment tears (P = .62); specificity of both imaging modalities was 77%. Sensitivity (CT arthrography, 86%; MR imaging, 79%) and specificity (CT arthrography, 50%; MR imaging, 25%) for detection of the central segment tears were determined. Dorsal segment tears were detected only with CT arthrography, while all tears were missed with MR imaging (P = .02). Interobserver agreement was better for multi-detector row CT arthrography (kappa = 0.37-0.78) than for MR imaging (kappa = -0.33 to -0.10). CONCLUSION: Performance in depiction of palmar and central segment tears of SL and LT ligaments is almost equal for multi-detector row CT arthrography and MR imaging, with much higher interobserver reliability for CT arthrography. CT arthrography is significantly superior to MR imaging in the detection of dorsal segment tears of SL and LT ligaments.

Aged↗
PubMed2005

Bilateral perirenal lymphangioma: a conservative approach.

The lymphangioma is a well-recognized benign tumor most frequently encountered in infancy and childhood. The kidneys are rarely involved. Despite its benign nature, most of the patients were treated by partial or radical nephrectomy. We describe a case of bilateral perirenal lymphangioma in a 33-year-old man for whom we chose a conservative approach.

Adult↗
PubMed2005

MRI of the intrinsic muscles of the hand: spectrum of imaging findings and clinical correlation.

OBJECTIVE: The purpose of our study was to describe the spectrum of intrinsic hand muscle abnormalities on MRI in patients with clinically evident abnormalities of the intrinsic hand muscles and to correlate clinical and radiologic findings. MATERIALS AND METHODS: MRI of 21 hands was performed in 19 patients with clinically evident or suspected intrinsic hand muscle abnormalities. All MRI was performed on a 1.5-T scanner using transaxial T1-weighted, T2-weighted, or STIR as well as contrast-enhanced T1-weighted sequences. Two observers reviewed all MR images retrospectively in a blinded fashion with regard to the exact anatomic location of the muscle abnormality, signal abnormalities, muscle atrophy, and the cause. Kappa statistics were used to calculate interobserver variability. MRI findings were compared with clinical findings using Spearman's rank test. A panel of experts assessed the impact of MRI on the diagnostic workup. RESULTS: On the basis of MRI findings, abnormalities (either MR signal abnormality or atrophy) of both the lumbrical and interosseus muscles were noted in 10 (48%) of 21 hands, of the thenar muscles in eight (38%) of 21 hands, and of the hypothenar muscles in 12 (57%) of 21 hands. The correlation between clinical and MRI findings was moderate to strong for the interosseus, thenar, and hypothenar muscles (0.43-0.84). MRI was judged to be useful for establishing the final diagnosis in 17 (81%) of 21 hands. CONCLUSION: MRI of the hands is useful and correlates well with clinical findings in patients with intrinsic hand muscle abnormalities.

Adolescent↗
PubMed2005

MRI for diagnosis and monitoring of patients with eosinophilic fasciitis.

OBJECTIVE: The objective of this study was to describe MRI findings in patients with eosinophilic fasciitis (EF) and to correlate clinical and laboratory findings with the MRI findings. MATERIALS AND METHODS: Six patients with histologically proven EF underwent MRI at the time of diagnosis and after therapy (15 MRI examinations). Unenhanced T1-weighted, T2-weighted, and STIR sequences were performed using a 1.5-T MRI system. In addition, all patients were imaged with contrast-enhanced T1-weighted sequences. MRI findings, clinical findings, and laboratory parameters were retrospectively reviewed. RESULTS: At the time the six patients presented, all eight MRI examinations revealed symmetric thickening and hyperintensity of the superficial muscle fasciae of the thigh, calves, or arms on unenhanced T1-weighted, T2-weighted, or STIR sequences, with strong enhancement after administration of IV contrast agent. In seven of the eight MRI examinations, similar signal changes were also present in the deep muscle fasciae. After treatment, the fascial abnormalities found on MRI disappeared on six of eight MRI examinations performed in five patients-a rate that correlated well with the clinical findings. In one patient with EF involvement of the thigh, the MRI abnormalities showed partial remission, which also correlated well with the clinical findings. CONCLUSION: In EF, MRI reveals characteristic findings including thickening, signal abnormalities, and contrast enhancement of the superficial and, to a lesser extent, deep muscle fasciae. MRI is useful for establishing the diagnosis, guiding the choice of biopsy site, and assessing treatment response.

Adult↗
PubMed2005

Dynamic MR imaging of outlet obstruction.

The outlet obstruction syndrome encompasses all pelvic floor abnormalities which are responsible for an incomplete evacuation of fecal contents from the rectum. It has been estimated that outlet obstruction may be observed in half of constipated patients. A detailed clinical examination still represents the cornerstone of the diagnosis of these patients. However, there is general agreement that a reliable evaluation of the different pelvic floor abnormalities and the treatment decision highly depend on the imaging assessment. Traditionally, conventional defecography has played an important role in the radiological assessment of these patients but the technique is limited by its projectional nature and its inability to detect soft-tissue structures. Dynamic pelvic MR imaging using either closed-configuration or open-configuration MR systems is a rapidly evolving technique which has been gaining increased interest over the last years. The free selection of imaging planes, the good temporal resolution, and the excellent soft-tissue contrast have transformed this method into the preferred imaging modality in the evaluation of patients with pelvic floor dysfunction including rectocele, enterocele, internal rectal prolapse, and anismus.

Constipation↗
PubMed2004

MR imaging of the wrist: comparison between 1.5- and 3-T MR imaging--preliminary experience.

Institutional review board approval and informed consent were obtained from 25 healthy volunteers and 15 consecutive patients with chronic wrist pain or suspected carpal mass, and 1.5- and 3-T magnetic resonance (MR) imaging of the wrist was prospectively performed with comparable sequence parameters and surface coils of the same geometric design. Imaging protocols at both field strengths included a T1-weighted spin-echo sequence, two intermediate-weighted fast SE sequences with different echo times and with and without fat saturation, and a three-dimensional fast field-echo sequence. The contrast-to-noise ratio (CNR) between muscle and bone and between bone and cartilage was calculated for both field strengths. The visibility of various anatomic structures, including the triangular fibrocartilage complex, carpal ligaments, nerves, and cartilage, was analyzed with a four-point grading scale. CNRs were significantly higher on 3-T MR images than on 1.5-T MR images (P < .001; analysis of variance) for all sequences. Visibility of the triangular fibrocartilage complex and intercarpal ligaments and cartilage was significantly better on 3-T MR images than on 1.5-T MR images (paired sign test).

Adult↗
PubMed2004

Detection of synovial macrophages in an experimental rabbit model of antigen-induced arthritis: ultrasmall superparamagnetic iron oxide-enhanced MR imaging.

PURPOSE: To evaluate intravenously administered ultrasmall superparamagnetic iron oxide (USPIO) as a marker of macrophage activity in an experimental rabbit model of antigen-induced arthritis. MATERIALS AND METHODS: Unilateral arthritis was induced by means of intraarticular injection of methylated bovine serum albumin in 10 knees of 10 rabbits that had been presensitized to the same antigen. The contralateral knees in these rabbits, as well as six knees in three other rabbits, served as controls. After onset of arthritis, all knees were imaged prior to and 24 hours after administration of USPIO. The magnetic resonance (MR) imaging protocol included T1-weighted spin-echo, T2-weighted fast spin-echo, T2*-weighted gradient-echo, and short inversion time inversion-recovery sequences. Images were analyzed quantitatively and qualitatively with regard to signal characteristics and pattern. MR findings were correlated with histopathologic findings. Wilcoxon signed rank test was used to compare results of signal-to-noise ratio calculations before and after USPIO administration. RESULTS: All knees with intraarticular injection of antigen suspension developed unilateral arthritis, whereas no signs of arthritis occurred in the control knees. On USPIO-enhanced images obtained 24 hours after contrast agent administration, significant T1 (P =.03) and more predominantly T2* (P =.02) and T2 effects (P =.01) were evident in the synovium of all 10 arthritic knees, which reflected USPIO uptake by macrophages in the synovial tissue. To a lesser extent, T2* effects were present also within the joint effusion (P =.01). No significant changes in signal characteristics were detected in the 10 nonarthritic knees in the antigen-injected group or the six knees in the control group (P =.06-.91). Histologic examination confirmed uptake of iron in the macrophages of arthritic knees. Changes in MR signal characteristics within the arthritic synovium and synovial effusion were visually detectable after intravenous administration of USPIO. CONCLUSION: MR imaging at 1.5 T can depict USPIO uptake in phagocytic-active macrophages in an antigen-induced arthritis animal model.

Adjuvants, Immunologic↗
PubMed2004

Coronary artery bypass grafts: ECG-gated multi-detector row CT angiography--influence of image reconstruction interval on graft visibility.

PURPOSE: To evaluate the influence of different reconstruction intervals of retrospectively electrocardiographically (ECG)-gated multi-detector row computed tomographic (CT) angiography on image quality of different segments of various types of coronary artery bypass grafts. MATERIALS AND METHODS: Twenty consecutive patients with 62 grafts underwent retrospectively ECG-gated four-channel multi-detector row CT angiography and conventional coronary angiography. Raw helical CT data were reconstructed at 0%-90% of the cardiac cycle in increments of 10%. Each graft was separated into three segments (proximal segment, graft body, and distal anastomosis). Three graft types were identified according to site of distal anastomosis. Two readers assessed image quality of segments and graft types. Effective radiation dose was calculated. RESULTS: Best image quality of all segments was obtained at a reconstruction interval of 50%-70% of the cardiac cycle. Image quality of the proximal segment did not vary significantly with different reconstruction intervals (analysis of variance, P =.8), whereas image quality of the graft body and distal anastomosis changed significantly with varying reconstruction intervals (P <.001). Distal anastomosis and body of types 1 and 2 grafts were best seen at 60%-70% of the cardiac cycle, whereas distal anastomosis and body of type 3 grafts were best visualized at 50%. Accuracy of CT angiography for detection of graft patency was 94% for reader 1 and 95% for reader 2. Effective dose for CT was 11.4 mSv for both men and women. Mean effective dose for angiography was 2.1 mSv for men and women. CONCLUSION: Optimal selection of reconstruction interval improves image quality of the graft body and of distal anastomosis in particular.

Aged↗
PubMed2004

Assessment of skeletal muscle perfusion by contrast medium first-pass magnetic resonance imaging: technical feasibility and preliminary experience in healthy volunteers.

PURPOSE: To probe the potential and pitfalls of contrast medium first-pass skeletal muscle perfusion imaging under reproducible stress conditions. MATERIALS AND METHODS: Magnetic resonance (MR) signal dynamics in calf muscle and lower-leg arteries of 20 healthy volunteers were analyzed under postarterial occlusion reactive hyperemia and concurrent contrast medium first pass, using a saturation recovery spoiled gradient-echo type sequence without heartbeat synchronization. The signal vs. time curves were analyzed descriptively and by two-compartment deconvolution analysis. RESULTS: Highly significant changes in calf muscle signal dynamics in the hyperemic leg vs. those in the contralateral leg at rest were found in phenomenological and deconvolution analysis. Although a distortion of the arterial signal derived input function by inflow effects was found to cause large variations of the deconvolution results, the magnitude of the observed effects suggested a potential for immediate visual detection of areas with reduced tissue perfusion. CONCLUSION: The first-pass approach appeared promising for visual evaluation. However, a disentanglement of inflow and contrast medium-induced effects on arterial signal intensity was deemed a prerequisite for input function-based numerical assessment.

Adult↗
PubMed2004

Pseudocystic degeneration of the lumbar ligamentum flavum: a little known entity.

OBJECTIVE: The objective of this work was to investigate the clinical and histologic features of patients with pseudocystic lesions of the ligamentum flavum in the lumbar region of the spinal canal and ascertain the existence of genuine ligamentum flavum pseudocysts. METHODS: Retrospective chart and histologic study of a patient cohort with lumbar radiculopathy due to a cystic intraspinal lesion and who had undergone decompressive surgery was conducted. Intraoperatively, the stenosing process had been found to be different from common etiologic entities and had been submitted for histologic examination. RESULTS: The 33 patients with symptoms and signs of lumbar radiculopathy were between 48 and 85 years of age (mean 63.5 years). Twenty (61%) of them were women. All patients showed degenerative changes of the bony structures of the spine by conventional radiography. Segmental instability due to degeneration of the lumbar spine was present in 45%. Computed tomography and/or magnetic resonance imaging showed a cystic lesion. Clinical and histologic examination confirmed their origin from within the severely degenerated ligamentum flavum. CONCLUSIONS: Radiologic, surgical, and histologic findings suggest that the pseudocystic degeneration of the ligamentum flavum represents a genuine entity that is associated with degenerative changes of the structures of the respective lumbar spine segment. These pseudocystic lesions may compress the adjacent nerve roots, provoking symptoms and signs of radiculopathy. The findings suggest that the surgical treatment not only must consist of removal of the pseudocyst but must also include a radical extirpation of the ligamentum flavum surrounding the pseudocyst to avoid recurrence of such a lesion.

Aged↗
PubMed2004

MR imaging of the knee: position related changes of the menisci in asymptomatic volunteers.

RATIONALE AND OBJECTIVES: To evaluate position related changes of the menisci in asymptomatic volunteers based on MR imaging of the knee in different positions. METHODS: Twenty-two knees from 22 asymptomatic volunteers with no history of knee injury and no evidence of meniscal tears were examined with a 0.5-T open-configuration MR system. Sagittal and coronal images were obtained with the knee supine in neutral, supine in 90-degree flexion with external and internal rotation, as well as in upright weight-bearing positions. The position of the menisci from the outer inferior edge of the meniscus to the outermost edge of the articular cartilage of the tibial plateau was measured, and meniscal movement was calculated. The Wilcoxon signed-rank test was used for statistical analysis. RESULTS: Meniscal movement in the sagittal plane was greatest in the anterior horn of the medial meniscus upon position change from supine neutral to supine in 90-degree flexion with external rotation (mean, 10.5 millimeters). The least meniscal movement was observed in the anterior horn of the lateral meniscus when changing from the supine neutral to the upright knee position (mean, 0.6 millimeters). Meniscal protrusion (ie, protrusion of any part of the meniscus beyond the tibial plateau) was noted most frequently for the anterior horn of the medial meniscus (14/22 instances; 63.6%) in the sagittal plane with the knee in neutral position (mean, 2.6 millimeters, range, 1.8-2.8 millimeters). In the coronal plane, medial meniscal protrusion was most frequently present in the upright weight-bearing position (11/22 instances (50%; mean, 2 millimeters; range, 1.2-2.6 millimeters). CONCLUSIONS: : Meniscal movement is most prominent in the anterior horn of the medial meniscus with the knee in the supine position in 90-degree flexion with external rotation. Meniscal protrusion is more frequently present in the medial meniscus and averaged less than 3 millimeters in normal volunteers in either the sagittal or coronal MR imaging plane.

Adult↗
PubMed2004

Clinical and functional results after floating shoulder injuries.

BACKGROUND: Good results have been reported with both operative and nonoperative treatment of floating shoulder, and discussions about an appropriate therapy of this rare entity are controversial because of small numbers of patients. METHODS: Seventeen patients with a floating shoulder were retrospectively evaluated. The treatment was nonoperative in eight patients and operative in nine. All patients were clinically examined and standard shoulder radiographs were obtained at the time of follow-up. RESULTS: All fractures healed. Five patients in the nonoperative and five patients in the operative group showed good to excellent results. The associated injuries influence the outcome of these patients significantly. CONCLUSION: Nondisplaced or less displaced floating shoulders are expected to give good results after nonoperative treatment. If mostly heavy associated injuries allow it, significantly displaced fractures should be treated operatively.

Adult↗
PubMed2004

MDCT in emergency radiology: is a standardized chest or abdominal protocol sufficient for evaluation of thoracic and lumbar spine trauma?

OBJECTIVE: The objective of our study was to assess the diagnostic performance of a standardized 4-MDCT trauma protocol for the evaluation of the thoracic and lumbar spine in patients with multiple injuries. MATERIALS AND METHODS: Eighty-two patients with multiple injuries underwent MDCT for the chest and abdomen using a standardized 4-MDCT trauma protocol (collimation, 4 x 2.5 mm). Secondary reconstructions targeted to the spine were performed (slice width, 3 mm; reconstruction interval, 1.5 mm). All spinal fractures were additionally scanned using a collimation of 4 x 1 mm, and these images served as the standard of reference for fracture classification. An additional 50 patients with no spinal fracture served as the control group. A total of 65 major spinal fractures were present in 55 of the patients with multiple injuries. Two observers (observer 1 and observer 2) independently evaluated all CT data for spinal fractures using a 5-point confidence scale, classified the different fracture types, and rated the image quality of spinal structures on axial images and multiplanar reformations. RESULTS: Image quality for axial images was excellent in 80% and in 68% using 4 x 1 mm and 4 x 2.5 mm collimation, respectively. Image quality of the multiplanar reformations was excellent in 75% and good in 65% using 4 x 1 mm and 4 x 2.5 mm collimation, respectively. Spinal fractures were detected by observer 1 and observer 2 with a sensitivity and specificity of 98% and 97% and of 97% and 97%, respectively. Interobserver agreement regarding the confidence scale for fracture detection was substantial (kappa = 0.80), and agreement between the different imaging protocols for fracture classification was excellent for observer 1 (kappa = 0.95) and observer 2 (kappa = 0.97). CONCLUSION: Accurate evaluation of the thoracolumbar spine is possible with targeted image reconstruction based on a standardized 4-MDCT trauma protocol of the chest and abdomen.

Adolescent↗