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Biomedical subjects

S Feuerbach

Publications and source records attributed to S Feuerbach.

At least 91 records · Page 5Linked to original sources
PubMed2000

Digital radiography with a large-area, amorphous-silicon, flat-panel X-ray detector system.

RATIONALE AND OBJECTIVES: To investigate the image quality of a digital radiography system with an amorphous-silicon, large-area, digital flat-panel detector. METHODS: A flat-panel detector based on a matrix of amorphous silicon was integrated into a projection radiography system. The scintillator consisted of a layer of structured cesium iodide. The active matrix size of 30002 pixels together with a pixel size of 143 microm provided a large image area of 43 x 43 cm2. Basic image quality parameters such as detective quantum efficiency (DQE) and modulation transfer function (MTF) were measured and compared with those obtained with conventional systems. RESULTS: The measurement of DQE yielded a high value of 70% at zero spatial frequency. At a system dose equivalent to 400 speed, the DQE of the digital system was a factor of two larger than the DQE of a storage phosphor or screen-film system within the entire spatial frequency range between zero and the Nyquist limit of 3.5 line pairs per millimeter. The flat-panel detector furthermore has an MTF that is superior to that in regular screen-film systems and also provides a substantially larger dynamic range. CONCLUSIONS: This new technology demonstrates its potential to provide equal or superior image quality to conventional screen-film systems and to reduce patient exposure to radiation dose. The advantages of digital radiography systems, based on a flat-panel detector as an instant image display, facilitation of work flow in the radiology department, and digital networking and archiving, are well in sight.

Humans↗
PubMed2000

Magnetic resonance monitoring of stent deployment: in vitro evaluation of different stent designs and stent delivery systems.

RATIONALE AND OBJECTIVES: To evaluate MR imaging features of commercially available stents before, during, and after in vitro deployment as a step toward MR-guided stent deployment. METHODS: Fourteen stents were deployed in a phantom under MR monitoring at 1.5 T by using a gradient-echo sequence. Device visibility was rated on a four-point scale (excellent, fair, poor, not visible). RESULTS: The Memotherm stent and the rolling membrane (RM) Wallstent showed excellent stent visibility and at least fair scores for artifact-induced narrowing of the stent lumen. Three stents (Palmaz, AVE, Easy Wallstent) showed excellent visibility of the stent but no visible lumen. Five stents (Strecker, Accuflex, Hemobahn, Passager, Sinus) displayed fair visibility. The delivery catheters of four stent systems (Smart, Vascucoil, Symphony, ZA) displayed severe black hole artifacts. CONCLUSIONS: The imaging features of several stent systems might be suitable for MR-guided intervention. The Memotherm and the Wallstent RM combine good visibility of the stent and the lumen.

Blood Vessel Prosthesis↗
PubMed2000

Reduction of motion artifacts in magnetic resonance imaging of the neck and cervical spine by long-term averaging.

RATIONALE AND OBJECTIVES: We performed a prospective comparison of T1-weighted turbo spin-echo (TSE) imaging with standard averaging and with the long-term averaging method (LOTA), comparing the effects on signal-to-artifact noise ratio (S/aN) and motion artifacts. METHODS: In 30 consecutive patients undergoing imaging of the neck or cervical spine, a transverse T1-weighted TSE sequence was applied with and without LOTA by using identical sequence parameters. Quantitative image analysis was done by calculating S/Ns in the phase-encoding direction (S/aN). Visual image analysis was performed by four independent, masked readers using a standardized score sheet for anatomic and pathological findings. RESULTS: The LOTA sequence yielded significantly superior S/aN values compared with the standard averaging sequence. In the subjective evaluation, the LOTA sequence showed significantly fewer motion artifacts and better visualization of normal anatomy of the neck, cervical spine, and spinal cord, as well as of the pathological findings. CONCLUSIONS: LOTA is a valuable method for increasing S/aN in magnetic resonance imaging of the neck and cervical spine. It reduces motion artifacts and increases the conspicuity of pathology without increasing acquisition time. No additional hardware is needed, and this technique can be combined with other artifact-reducing methods.

Adult↗
PubMed2000

Chest radiography with a large-area detector based on cesium-iodide/amorphous-silicon technology: image quality and dose requirement in comparison with an asymmetric screen-film system.

The purpose of this study was to evaluate a large-area, flat-panel X-ray detector, which uses cesium-iodide (CsI) and amorphous silicon (a-Si). Conventional images were compared with digital images acquired with equal dose (2.5 microGy) and with 50% dose reduction. Fifteen consecutive patients were studied prospectively using an asymmetric screen-film system (detector dose, 2.5 microGy). Digital images were taken from the same patients in a posteroanterior view with detector doses of 2.5 and 1.25 microGy, respectively. The CsI/a-Si active-matrix imager had a panel-size of 43 x 43 cm, a matrix of 3 x 3k, and a pixel-pitch of 143 microm. Hard copies were presented in a random order to eight independent observers, who rated image quality according to six subjective quality criteria. Statistical significance of differences was evaluated with Student's t test for paired samples (confidence level, 95%). Digital radiographs with 2.5 and 1.25 microGy were superior to conventional images regarding all quality criteria. Statistically significant differences were observed for five of six criteria at a detector dose of 2.5 microGy and for only one quality feature at 1.25 microGy. Flat-panel digital imagers based on CsI/a-Si technique have the potential to replace conventional systems and might allow a reduction of radiation dose by 50% without loss of image quality.

Adult↗
PubMed2000

Simulated bone erosions in a hand phantom: detection with conventional screen-film technology versus cesium iodide-amorphous silicon flat-panel detector.

PURPOSE: To assess the diagnostic performance of an active-matrix flat-panel x-ray detector for reduced-dose imaging of simulated arthritic lesions. MATERIALS AND METHODS: A digital x-ray detector based on cesium iodide and amorphous silicon technology with a panel size of 43 x 43 cm, matrix of 3,000 x 3,000 pixels, pixel size of 143 micrometer, and digital output of 14 bits was used. State-of-the-art screen-film radiographs were compared with digital images obtained at doses equivalent to those obtained with system speeds of 400, 560, and 800. The phantom was composed of a human hand skeleton on an acrylic plate with drilled holes simulating bone erosions of different diameters and depths. Results of four independent observers were evaluated with receiver operating characteristic curve analysis. RESULTS: The cesium iodide and amorphous silicon detector resulted in better diagnostic performance than did the screen-film combination, with the dose being the same for both modalities (P <.05). For digital images obtained at reduced doses, no significant differences were found. CONCLUSION: The improved diagnostic performance with digital radiographs obtained with the cesium iodide and amorphous silicon detector suggests that this detector technology holds promise in terms of dose reduction for specific diagnostic tasks, without loss of diagnostic accuracy.

Arthritis↗
PubMed2000

Stent appearance at contrast-enhanced MR angiography: in vitro examination with 14 stents.

PURPOSE: To evaluate signal intensity changes influencing assessment of stent patency at contrast material-enhanced magnetic resonance (MR) angiography. MATERIALS AND METHODS: By using an in vitro model, 14 stents-nine nitinol, one tantalum, two stainless steel, and two cobalt alloy-were investigated regarding their appearance at MR imaging. A vascular phantom consisting of tubes filled with 2.00 mmol/L gadopentetate dimeglumine in saline solution was studied in different orientations within the magnetic field. Imaging was performed with a fast three-dimensional gradient-echo sequence (4. 70/1.89 [repetition time msec/echo time msec]). Relative signal intensity reduction within the stents and the degree of artificial narrowing of the stent lumen were calculated. RESULTS: The stent lumen was visible within 13 stents. A total signal void inside the stent lumen appeared in only one cobalt alloy stent. Artificial narrowing of the diameter was less than 33% in 10 of 14 stents. The tantalum stent and four nitinol stents seemed best suited for contrast-enhanced MR angiography. A bandlike artifact occurred at the ends of the stents when positioned along the readout direction. CONCLUSION: To differentiate between artifacts and stenoses, knowledge of the degree of signal intensity reduction and artificial lumen narrowing within vascular stents is essential. Stent geometry, relative orientation to the magnetic field, and alloy composition influence signal intensity alteration within the stent lumen.

Contrast Media↗
PubMed2000

Time-resolved contrast-enhanced MR angiography of renal artery stenosis: diagnostic accuracy and interobserver variability.

OBJECTIVE: The purpose of this study was to evaluate diagnostic accuracy and interobserver variability of time-resolved three-dimensional gadolinium-enhanced MR angiography in the detection of renal artery stenosis in comparison with intraarterial digital subtraction angiography as the standard of reference. SUBJECTS AND METHODS: Forty consecutive patients (age range, 25-81 years; mean, 62.9 +/- 11.9 years) with suspected renal artery stenosis underwent intraarterial digital subtraction angiography and gadolinium-enhanced MR angiography, performed on a 1.5-T system with fast low-angle shot three-dimensional imaging (3.8/1.49 [TR/TE], 25 degrees flip angle, 10-sec acquisition time, and 1.5-mm partition thickness). Three time-resolved phases were obtained in a single breath-hold. Digital subtraction angiography and gadolinium-enhanced MR angiography were evaluated by four observers who studied 80 main renal arteries and 19 accessory vessels to evaluate the degree of stenosis. A stenosis reducing the intraarterial diameter by more than 50% was regarded as hemodynamically significant. Interobserver variability was calculated. RESULTS: Only one gadolinium-enhanced MR angiography study was not of diagnostic quality, as a result of failure of the power injector. All main branches were of diagnostic quality in 38 (97.4%) of the remaining 39 gadolinium-enhanced MR angiography studies. Seventeen (89.5%) of 19 accessory renal arteries were depicted with gadolinium-enhanced MR angiography. The overall sensitivity for significant stenoses was 92.9%. The overall specificity was 83.4%, and the overall accuracy was 85.9%. Interobserver variability of gadolinium-enhanced MR angiography exceeded that of digital subtraction angiography. CONCLUSION: Time-resolved three-dimensional gadolinium-enhanced MR angiography is a useful noninvasive method of screening suspected renal artery stenosis because of its easy application, short examination time, and high sensitivity despite of its higher interobserver variability.

Adult↗
PubMed2000

Analysis of the availability and completeness of previous radiological examinations related to plain films.

PURPOSE: To evaluate the availability and completeness of previous radiological examinations. MATERIAL AND METHODS: Seven different types of examinations were analysed separately: 1) chest examinations, 2) bedside chest examinations, 3) skeletal examinations, 4) angiographic examinations, 5) mammographic examinations, 6) CT examinations, and 7) MR examinations. A retrospective part of the study covered the calendar year 1997, while a prospective part referred to 1998. The sample size in each modality and each part of the study was 100 observations, resulting in a total number of 1,400 examinations. RESULTS: The average availability and completeness of radiographs in the retrospective analysis was 96.9% in 1997. The average availability and completeness of radiographs in the prospective analysis was 85.5% for the year 1998. This applied to necessary previous examinations of the same or different modality irrespective whether the examination was conducted internally or externally. CONCLUSION: The real loss rate of radiographs derived from the retrospective investigation was 3.1%. The prospective part of the study showed that 14.5% of the required previous internal and external examinations of the same or different modality were not available completely and in time to the examining radiologist.

Humans↗
PubMed1999

Multiple hepatic angiolipomas: a case report and review of literature.

Follow-up of two hepatic angiolipomas in a patient without evidence of tuberous sclerosis is reported. Initially, the lesions presented as homogenously enhancing masses, which were nearly isodense to normal liver tissue on plain CT scans. Focal nodular hyperplasia was assumed. One year later, fat was detected in the growing tumors and percutaneous core biopsy revealed hepatic angiolipomas. Natural history of these rare lesions is unknown, and this is to the best of our knowledge the first observation of fatty metamorphosis in such a benign, mesenchymal hepatic neoplasm.

Adult↗
PubMed1999

Idiopathic hypertrophic cranial pachymeningitis associated with an orbital pseudotumor.

We report a case of idiopathic hypertrophic cranial pachymeningitis (IHCP) associated with an orbital pseudotumor and granulocytic thyroiditis of unknown origin. The patient suffered from progressive and finally complete loss of visual acuity, as well as from multiple cranial nerve dysfunctions. Medical treatment and radiation therapy were not beneficial. As reported in the literature, the CT and MRI findings of IHCP were non-specific; thus, diagnosis had to be made by exclusion and open biopsy was required. An inflammatory pseudotumor of the orbit is rarely found in patients with IHCP. Thyroiditis has not yet been reported in the context of IHCP. The patient also suffered from anosmia, which is an unusual feature of IHCP.

Autoimmune Diseases↗
PubMed1999

[Contrast medium-enhanced MR angiography of the pelvic and leg vessels with an automated table-feed technique].

PURPOSE: To evaluate contrast enhanced magnetic resonance angiography (ceMRA) with an automated table-feed technique in patients with arterio-occlusive disease for imaging of the pelvic and peripheral arteries. METHODS: Twenty-two patients underwent three-dimensional gadolinium-enhanced MR angiography in a three-step automatic table-feed technique on a Magnetom Symphony operating at 1.5 Tesla. Maximum intensity projection images (MIP) were generated from the subtracted and original studies. Image quality and venous contrast were evaluated by two groups of observers. 304 vessels (17 patients) were compared with DSA as the standard of reference. RESULTS: All examinations were performed without any technical problems. Diagnostic quality of the MIP of subtracted data sets was superior to that of the unsubtracted images. Venous overlay was 61% in the lower leg. In a total of 599 observations, a sensitivity of 96% (95%, 82%) and a specificity of 87% (88%, 99%) were high compared to DSA in the detection of significant stenoses > or = 50% (> or = 75%, occlusions). Interobserver correlation was good (linear correlation 0.9). CONCLUSION: Stepping-table digital subtraction contrast enhanced MRA is a promising technique in the diagnosis of peripheral arterio-occlusive disease.

Aged↗
PubMed1999

[Digital flat image detector technique based on cesium iodide and amorphous silicon: experimental studies and initial clinical results].

PURPOSE: Experimental and clinical evaluation of a digital flat-panel X-ray system based on cesium iodide (CsI) and amorphous silicon (a-Si). METHODS: Performance of a prototype detector was compared with conventional screen-film radiography (SFR) using several phantom studies. Foreign bodies, fractures, osteolyses, and pulmonary lesions were analyzed. Additionally, 120 patients were studied prospectively, resulting in 400 comparative X-ray studies. The flat-panel detector was exposed with standard dose and with a dose reduction of up to 75%. Detector size was 15 x 15 cm, pixel matrix was 1 x 1 k with a pixel size of 143 microns. Modulation-transfer function was determined to be 18% at the maximum spatial resolution of 3.5 lp/mm. RESULTS: The diagnostic results achieved with the digital detector were similar to those of conventional SFR, even at reduced radiation exposure. A potential for dose reduction was observed: 50% with respect to osteoarthrosis and fractures, and 75% for determining bony alignment. DISCUSSION: This new technology can be used in thoracic and skeletal radiography. A significant dose reduction is possible, depending on the suspected disease.

Animals↗
PubMed1999

[Transfemoral pelvic vein angiography with CO2: experiences with pressure- and volume-controlled injections].

PURPOSE: To evaluate the efficacy of CO2 in aortobifemoral DSA with a pressure- and volume-controlled injector. MATERIALS AND METHODS: In an intraindividual prospective study, 42 patients with arterial occlusive disease underwent stepwise aortobifemoral DSA with CO2 and with iopromid 300. RESULTS: With Co2, diagnostic images were obtained in 74% of the iliac, 98% of the femoral, 89% of the popliteal arteries, but in only 36% of the arteries of the lower leg. 73% of the stenoses were correctly identified. With therapeutic relevance 8% of the stenoses were overestimated. The length of 1 of 53 occlusions was overestimated and 3 occlusions were simulated. No stenoses or occlusion was missed. There were no severe side-effects. The injector proved to be safe and easy to handle. Fragmentation of the CO2 bolus could be compensated by postprocessing with a minimum opacification summation mode. CONCLUSIONS: With the equipment used, CO2 was a safe alternative to iodinated CM in routine stepwise aortobifemoral DSA of the iliac, femoral, and popliteal arteries. Because of the risk of overestimation, occlusions and high grade stenoses should be verified with selective injections or iodinated CM before PTA or operations.

Adult↗
PubMed1999

[Ischemic complications in aortic dissection--percutaneous treatment with balloon fenestration and stent implantation].

PURPOSE: To describe principles and results of percutaneous treatment of ischemic complications of aortic dissection. MATERIALS AND METHODS: In five cases (four patients) aortic dissection was clinically complicated by renal (n = 4), iliofemoral (n = 2) or mesenterial ischemia (n = 1). After evaluation by means of computed tomography, angiography, and manometry, treatment consisted of balloon fenestration of the intimal flap, stent placement or both. RESULTS: Eleven of 25 vascular beds were classified as ischemic. Treatment consisted of 11 balloon fenestration procedures in 3 patients, in one case supported by stent placement across the dissection membrane. Stents were placed in five renal arteries, one stent was placed in the true lumen of the aorta. One iliac artery was treated with balloon dilatation. One renal artery dissection became symptomatic after balloon fenestration and was treated successfully by stent placement. In all cases ischemia was resolved by endovascular treatment. All patients had persistent relief of symptoms. Mean follow-up time is 5.8 months. CONCLUSION: Ischemic complications of aortic dissection can be effectively and safely treated with stent placement and balloon fenestration.

Adult↗