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Biomedical subjects

Okka W Hamer

Publications and source records attributed to Okka W Hamer.

15 recordsLinked to original sources
PubMed2006

Indirect MR arthrography of the shoulder: use of abduction and external rotation to detect full- and partial-thickness tears of the supraspinatus tendon.

PURPOSE: To evaluate prospectively the accuracy of indirect magnetic resonance (MR) arthrography for supraspinatus tendon tears during neutral positioning or abduction and external rotation (ABER) and neutral positioning. MATERIALS AND METHODS: Informed consent was obtained in all patients, and the study was approved by the institutional review board. Indirect MR arthrography of the shoulder was performed in 51 symptomatic patients (14 female, 37 male; mean age, 47 years) in the neutral position (set 1) and in the neutral and ABER positions (set 2). Two readers independently interpreted both sets, and diagnoses were compared with arthroscopic findings. Diagnostic accuracy was calculated, and 95% confidence intervals were used to detect significant differences between sets. Diagnostic confidence was recorded by using a three-level confidence score. Differences between sets were evaluated by using the Wilcoxon signed rank test. Interobserver agreement was determined separately for each set and for all diagnoses, full-thickness tears, and partial-thickness tears. RESULTS: For full-thickness tears, there was no benefit to reading set 2. For reader 1, sensitivity and specificity were 95% and 100%, respectively, for set 1 and 100% and 100%, respectively, for set 2. For reader 2, sensitivity and specificity were 80% and 100%, respectively, for set 1 and 100% and 100%, respectively, for set 2. For partial-thickness tears, sensitivity was significantly higher after reading set 2. For reader 1, sensitivity and specificity were 71% and 88%, respectively, for set 1 and 93% and 100%, respectively, for set 2. For reader 2, sensitivity and specificity were 50% and 88%, respectively, for set 1 and 86% and 94%, respectively, for set 2. For both readers, diagnostic confidence for partial-thickness tears was significantly higher after reading set 2. After the interpretation of set 2, kappa values increased from 0.35 to 1.00 for full-thickness tears and from 0.12 to 0.63 for partial-thickness tears. CONCLUSION: Indirect MR arthrography with supplementary images obtained with patients in the ABER position significantly improved sensitivity and increased diagnostic confidence for partial-thickness tears of the supraspinatus tendon. Interobserver agreement was improved for both full- and partial-thickness tears.

Adolescent↗
PubMed2005

Chest radiography with a flat-panel detector: image quality with dose reduction after copper filtration.

PURPOSE: To compare image quality and estimated dose for chest radiographs obtained by using a cesium iodide-amorphous silicon flat-panel detector at fixed tube voltage and detector entrance dose with and without additional 0.3-mm copper filtration. MATERIALS AND METHODS: The study was approved by the institutional ethics committee. All prospectively enrolled patients signed the written consent form. Chest radiographs in two projections were acquired at 125-kVp tube voltage and 2.5-microGy detector entrance dose. The experimental group (38 patients) was imaged with 0.3-mm copper filtration; the control group (38 patients) was imaged without copper filtration. An additional 12 patients were imaged with and without copper filtration and served as paired subject-controls. Three readers blinded to group and clinical data independently evaluated the radiographs for image quality on a digital display system. Twelve variables (six for each radiographic projection) were assigned scores on a seven-point ordinal scale. Scores between experimental and control groups were compared: Logistic regression analysis and Mann-Whitney U test were used for unpaired patients; and Wilcoxon and McNemar test, for paired patients. In all, 72 comparisons were determined (36 [12 variables x three readers] for unpaired patients and 36 for paired patients). In a phantom study, radiation burden of experimental protocol was compared with that of control protocol by using Monte Carlo calculations. RESULTS: For 70 of 72 comparisons, digital radiographs obtained with copper filtration were of similar image quality as radiographs obtained without copper filtration (P = .123 to P > .99). For two of 72 comparisons, one observer judged the experimental protocol superior to the control protocol (P = .043, P = .046). Patient dose reduction estimated with Monte Carlo calculations was 31%. Use of copper filtration increased exposure times by 48% for posteroanterior views and by 34% for lateral views. CONCLUSION: Subjectively equivalent chest radiographic image quality was found with estimated 30% dose reduction after addition of 0.3-mm copper filtration with flat-panel cesium iodide-amorphous silicon technology.

Cesium↗
PubMed2005

Imaging features of perivascular fatty infiltration of the liver: initial observations.

PURPOSE: To retrospectively identify and describe the imaging features that represent perivascular fatty infiltration of the liver. MATERIALS AND METHODS: The institutional review board approved the study and waived informed consent. The study complied with the Health Insurance Portability and Accountability Act. Ten patients (seven women, three men; mean age, 78 years; range, 31-78 years) with fatty infiltration surrounding hepatic veins and/or portal tracts were retrospectively identified by searching the abdominal imaging teaching file of an academic hospital. The patients' medical records were reviewed by one author. Computed tomographic (CT), magnetic resonance (MR), and ultrasonographic (US) imaging studies were reviewed by three radiologists in consensus. Fatty infiltration of the liver on CT images was defined as absolute attenuation less than 40 HU without mass effect and, if unenhanced images were available, as relative attenuation at least 10 HU less than that of the spleen; on gradient-echo MR images, it was defined as signal loss on opposed-phase images compared with in-phase images; and on US images, it was defined as hyperechogenicity of liver relative to kidney, ultrasound beam attenuation, and poor visualization of intrahepatic structures. Perivascular fatty infiltration of the liver was defined as a clear predisposition to fat accumulation around hepatic veins and/or portal tracts. For multiphase CT images, the contrast-to-noise ratio was calculated for comparison of spared liver with fatty liver in each imaging phase. RESULTS: Fatty infiltration surrounded hepatic veins in three, portal tracts in five, and both hepatic veins and portal tracts in two patients. Six of the 10 patients had alcoholic cirrhosis, two reported regular alcohol consumption (one of whom had acquired immunodeficiency syndrome and hepatitis B), one was positive for human immunodeficiency virus, and one had no risk factors for fatty infiltration of the liver. In three of the 10 patients, fatty infiltration was misdiagnosed as vascular or neoplastic disease on initial CT images but was correctly diagnosed on MR images. CONCLUSION: Perivascular fatty infiltration of the liver has imaging features that allow its recognition.

Adipose Tissue↗
PubMed2005

Percutaneous treatment of a patient with infected necrotizing pancreatitis.

BACKGROUND: A 50-year-old man with an acute episode of alcohol-induced chronic edematous pancreatitis and an inflammatory stenosis of the biliary tract was treated by implantation of a plastic endoprosthesis at a rural hospital in Germany. Because of his worsening condition, the patient was referred to the intensive care unit of the University Hospital, Regensburg, Germany. Contrast-enhanced CT revealed complete necrosis of the body and tail of the pancreas, formation of large retrogastric and paraduodenal fluid collections, and fluid along Gerota's fascia, as well as in the paracolic gutters. Antibiotic treatment was adjusted according to the results of microbiological testing after diagnostic puncture of the necrotic cavity. INVESTIGATIONS: CT scan, CT-guided fine-needle aspiration and fluoroscopy. DIAGNOSIS: Infected acute necrotizing pancreatitis. MANAGEMENT: Interventional treatment using large-bore percutaneous catheters to perform percutaneous necrosectomy, fragmentation of necrotic pancreatic tissue with a snare catheter and dormia basket, and aspiration. Parenteral nutrition and antibiotics were also administered.

Bacterial Infections↗
PubMed2005

Magnetic resonance-guided percutaneous angioplasty of femoral and popliteal artery stenoses using real-time imaging and intra-arterial contrast-enhanced magnetic resonance angiography.

OBJECTIVE: The aim of this study was to demonstrate the possibility of performing magnetic resonance (MR)-guided interventional therapy for femoral and popliteal artery stenoses with commercially available materials supported by MR real-time imaging and intra-arterial MR angiography. MATERIALS AND METHODS: A total of 15 patients suffering from symptomatic arterial occlusive disease of the lower limbs with 19 stenoses were included. Interventional intra-arterial digital subtraction angiography was performed before and after angioplasty on each patient as standard of reference. MR images were acquired on a 1.5-T MR scanner. A fast-low-angle shot (FLASH) 3D sequence was applied for a contrast enhanced MR-angiography (ceMRA). A total of 5 mL of diluted gadodiamide was injected via the arterial access. Maximum intensity projections (MIPs) were used as roadmaps and localizers for the interactive positioning of a continuously running 2D-FLASH sequence with a temporal solution of 2 images/second. The lesion was crossed by a balloon-catheter, which was mounted on a guidewire. The visibility was provided by the radiopaque markers on the balloon and was improved by injection of 1 mL of gadolinium into the balloon. Postinterventional control was performed by intra-arterial MR angiography and catheter angiography. RESULTS: Stenoses were localized by intra-arterial MR angiography. The guidewire/balloon combination was visible, and the balloon was placed correctly to cover the entire stenoses. Balloon dilation reduced the degree of stenosis by approximately 57% on average. No complications were observed. CONCLUSION: MR-guided balloon dilation of femoral and popliteal artery stenoses supported by real-time MR imaging and intra-arterial MR angiography is feasible with commercially available materials.

Aged↗
PubMed2005

In vivo evaluation of the carotid wallstent on three-dimensional contrast material-enhanced MR angiography: influence of artifacts on the visibility of stent lumina.

PURPOSE: Contrast material-enhanced magnetic resonance (MR) angiography is increasingly used in postinterventional imaging after implantation of endovascular stents. The main limitations are stent-related artifacts compromising the visibility of the stent lumen. The aim of this in vivo study is the evaluation of contrast-enhanced MR angiography imaging characteristics of the carotid Wallstent. MATERIALS AND METHODS: The carotid arteries of 29 patients were examined with contrast-enhanced MR angiography 3-6 days and/or 7-23 months after implantation of a carotid Wallstent into the internal carotid artery. Images were evaluated with regard to the diameter and signal intensity (SI) of the visible stent lumen. Digital subtraction angiography (DSA) was used as the standard of reference. RESULTS: Stent-related artifacts on contrast-enhanced MR angiography caused an artificial lumen narrowing and a reduction of the SI within the stent. Artifacts were pronounced on imaging 3-6 days after stent implantation, but 68% of stents imaged 7-23 months after stent implantation presented with a significantly decreased artificial signal reduction and an improved visibility of the stent lumen. CONCLUSIONS: The results of this study indicate that a reliable evaluation of the stent lumen is limited as a result of an artificial decrease of the SI inside the stent. However, in follow-up examinations 7-23 months after stent implantation, visibility of the stent lumen was improved and diagnostic reliability of contrast-enhanced MR angiography was markedly increased. A probable explanation for this phenomenon might be the formation of a neointimal layer covering the stent struts and thereby reducing stent-related artifacts.

Adult↗
PubMed2005

Intraarterial gadolinium-enhanced MR angiography in humans for the detection of infrainguinal arterial stenoses before and after percutaneous angioplasty.

OBJECTIVE: The objectives of this study were to show the feasibility of intraarterial MR angiography of the infrainguinal arteries and to compare the accuracy of intraarterial MR angiography with selective intraarterial digital subtraction angiography for the detection of stenoses before and after percutaneous balloon angioplasty. SUBJECTS AND METHODS: Fifteen patients underwent digital subtraction angiography and intraarterial MR angiography before and after balloon angioplasty. For intraarterial MR angiography, 30 mL of diluted contrast agent (5 mL of gadodiamide diluted in 55 mL of 0.9% saline solution) was injected through a sheath in the superficial femoral artery using a flow rate of 2.5 mL/sec. A 3D gradient-echo sequence was performed. Four independent blinded observers assessed differences in the quantitative measurement of stenoses and localization of lesions between digital subtraction angiography and intraarterial MR angiography. The overall impression of the intraarterial MR angiography images was documented on a 4-point scale (1 = excellent, 4 = poor). Interobserver variability was calculated. RESULTS: Intraarterial MR angiography from the upper leg to the trifurcation was feasible in all 30 examinations with a mean overall impression of all segments of 1.3 (SD, 0.68). For the detection of significant stenoses (> or = 50% stenosis), the overall sensitivity and specificity for the femoropopliteal and crural vessels were 92.4% and 91.7% and 91.9% and 87.8%, respectively. For the complete leg, sensitivity and specificity were 92.2% and 88.6%, respectively. Interobserver variability for intraarterial MR angiography of the crural vessels exceeded that of the femoropopliteal arteries. CONCLUSION: Intraarterial MR angiography of the infrainguinal arteries is feasible in humans using injections of diluted contrast agent at concentrations as low as 8%. It has a high sensitivity for detecting stenoses and an acceptable interobserver variability.

Adult↗
PubMed2005

In vivo evaluation of patency and in-stent stenoses after implantation of nitinol stents in iliac arteries using MR angiography.

OBJECTIVE: Our study was a prospective in vivo study to evaluate whether MR angiography is suitable for assessing stent patency and grading in-stent stenoses and to examine whether the accuracy of MR angiography changes with time after stent implantation. SUBJECTS AND METHODS: In a prospective study, 34 iliac stenoses in 27 patients were treated by implantation of 35 nitinol stents. MR angiography was performed immediately after stent placement for 32 stents, and both digital subtraction angiography (DSA) and MR angiography were repeated at the 6-month follow-up for 23 stents. Three blinded observers assessed stent patency and the degree of in-stent stenoses on MR angiography and DSA (the standard of reference) images. The difference between the observers' grading of stenoses on DSA and on MR angiography was determined. Statistical analysis was performed using the Student's t test for paired samples. RESULTS: Stent patency was assessed correctly for all stents and both sets of MR angiography images. Evaluation of DSA 1 images (obtained at end of implantation procedure) revealed that 96.9% of in-stent stenoses were less than 50%. On DSA 2 images (obtained at follow-up), 95.7% of in-stent stenoses were graded as less than 50%. The difference between grading of stenoses on DSA and MR angiography images was 15.0% +/- 16.0% (minimum, 0.0%; maximum, 63.3%) for DSA 1 versus MR angiography 1 (statistically significant, p = 0.037) and 9.8% +/- 13.5% (minimum, 0.0%; maximum, 63.3%) for MR angiography 2 versus DSA 2 (not statistically significant, p = 0.355). CONCLUSION: Patency was correctly assessed for all stents on MR angiography. The quality of MR angiography regarding characterization of in-stent stenoses improved with time after stent placement. However, discrepancies of more than 60% between grading of lumen narrowing on DSA and MR angiography images occurred even at the 6-month follow-up. Thus, MR angiography is not yet a reliable technique for characterization of in-stent stenoses.

Adult↗
PubMed2004

Dose reduction in skeletal and chest radiography using a large-area flat-panel detector based on amorphous silicon and thallium-doped cesium iodide: technical background, basic image quality parameters, and review of the literature.

The two most frequently performed diagnostic X-ray examinations are those of the extremities and of the chest. Thus, dose reduction in the field of conventional skeletal and chest radiography is an important issue and there is a need to reduce man-made ionizing radiation. The large-area flat-panel detector based on amorphous silicon and thallium-doped cesium iodide provides a significant reduction of radiation dose in skeletal and chest radiography compared with traditional imaging systems. This article describes the technical background and basic image quality parameters of this 43 x 43-cm digital system, and summarizes the available literature (years 2000-2003) concerning dose reduction in experimental and clinical studies. Due to its high detective quantum efficiency and dynamic range compared with traditional screen-film systems, a dose reduction of up to 50% is possible without loss of image quality.

Cesium↗
PubMed2004

Amorphous silicon, flat-panel, x-ray detector: reliability of digital image fusion regarding angle and distance measurements in long-leg radiography.

RATIONALE AND OBJECTIVES: To evaluate composed long-leg images acquired with a large-area, flat-panel x-ray detector with regard to angle and distance measurements. METHODS: Radiographs of a long-leg phantom were acquired at 13 different angle settings with a 43-cm x 43-cm digital x-ray detector based on cesium iodide (CsI) and amorphous silicon (a-Si) technology. Three overlapping single images of the phantom were reconstructed at a workstation using a generalized correlation method. Four blinded observers were instructed to determine the angle of the axis of the long-legs as well as the length of "femur" and "tibia" on soft-copy displays. For that, the angle and distance measurement software integrated in the workstation was used. The images were analyzed with and without prior manual fine tuning of the primary composition result according to a mapped scale. Standard of reference was angle and distance determination at the phantom. RESULTS: On average, the difference between the observers' angle measurements and the standard of reference was 0.4 degrees for both images with and without prior manual correction. Regarding distance measurements, the average discrepancies to the standard were 0.2 cm (femur) and 0.1 cm (tibia) when analyzing images that had undergone manual fine tuning and 0.5 cm and 0.7 cm, respectively, for images without manual correction. CONCLUSIONS: The evaluated image fusion algorithm in conjunction with a 43-cm x 43-cm flat-panel detector is feasible regarding angle and distance measurements on long-leg images. In the case of inaccurate primary composition, results can be corrected easily by manual fine tuning.

Algorithms↗
PubMed2004

Contrast-detail phantom study for x-ray spectrum optimization regarding chest radiography using a cesium iodide-amorphous silicon flat-panel detector.

RATIONALE AND OBJECTIVES: The purpose of this study evaluating a cesium iodide-amorphous silicon-based flat-panel detector was to optimize the x-ray spectrum for chest radiography combining excellent contrast-detail visibility with reduced patient exposure. MATERIALS AND METHODS: A Lucite plate with 36 drilled holes of varying diameter and depth was used as contrast-detail phantom. For 3 scatter body thicknesses (7.5 cm, 12.5 cm, 21.5 cm Lucite) images were obtained at 113 kVp, 117 kVp, and 125 kVp with additional copper filter of 0.2 and 0.3 mm, respectively. For each setting, radiographs acquired with 125 kVp and no copper filter were taken as standard of reference. On soft-copy displays, 3 observers blinded to the exposure technique evaluated the detectability of each aperture in each image according to a 5-point scale. The number of points given to all 36 holes per image was added. The scores of images acquired with filtration were compared with the standard images by means of a multivariate analysis of variance. Radiation burden was approximated by referring to the entrance dose and calculated using Monte Carlo method. RESULTS: All 6 evaluated x-ray spectra resulted in a statistically equivalent contrast-detail performance when compared with the standard of reference. The combination 125 kVp with 0.3 mm copper was most favorable in terms of dose reduction (approximately 33%). CONCLUSION: Within the constraints of the presented contrast-detail phantom study simulating chest radiography, the CsI/a-Si system enables an addition of up to 0.3 mm copper filtration without the need for compensatory reduction of the tube voltage for providing constant image quality. Beam filtration reduces radiation burden by about 33%.

Cesium↗
PubMed2004

Iliac artery stent placement: clinical experience and short-term follow-up regarding a self-expanding nitinol stent.

PURPOSE: To evaluate the effectiveness, safety, and short-term patency rates of a self-expandable nitinol stent (JostentSelfX; Abbott Laboratories, Chicago, IL) for treatment of iliac artery stenoses. MATERIALS AND METHODS: In a prospective study, 34 chronic iliac artery stenoses were primarily treated in 27 patients (mean age, 61.7 years +/- 9.4) by placement of a JostentSelfX. Handling and visibility of the stent was scored on a 4-point scale. Before stent placement, within 3 days after stent placement and at 6 months follow-up, the clinical history, clinical stage according to the Rutherford classification, and the ankle-brachial index (ABI) were assessed. Intra-arterial digital subtraction angiography including measurement of the mean pressure gradient was performed at the time of stent placement and at 6 months follow-up or in case of recurrence of symptoms. The Wilcoxon signed rank test and Kaplan-Meier method were applied for statistical analysis. RESULTS: The immediate technical success rate was 94%. The clinical success rate immediately after the procedure was 96% and 85% at 6 months follow-up. Stent placement significantly decreased the severity of stenoses as well as the mean pressure gradients and significantly increased the ABI. Handling of the stent was judged good. No misplacement occurred. Foreshortening during deployment was negligible and no stent migration was seen. However, visibility of the stent during fluoroscopy was ranked as moderate to bad. Follow-up at 6 months revealed the cumulative angiographic primary patency rate (<50% restenosis and <10 mm Hg mean pressure gradient) to be 0.96. CONCLUSION: The evaluated self-expandable nitinol stent is an effective tool in treating iliac artery stenoses. Apart from poor visibility, handling was good. The angiographic patency rate is comparable with data reported in other stent trials.

Alloys↗
PubMed2003

Amorphous silicon, flat-panel, x-ray detector versus storage phosphor-based computed radiography: contrast-detail phantom study at different tube voltages and detector entrance doses.

RATIONALE AND OBJECTIVES: Evaluation of the contrast-detail performance of an active-matrix flat-panel x-ray detector in comparison with a storage phosphor system with special regard to the potential of dose reduction. METHODS: A digital x-ray detector based on cesium iodide (CsI) and amorphous silicon (a-Si) technology was compared with a fifth-generation storage phosphor system. A lucite plate with 36 drilled holes of varying diameters and depths was used as contrast-detail phantom. At 45 kVp, 70 kVp, and 113 kVp, images at 8 different detector entrance doses ranging between 0.3 microGy and 40 microGy were obtained. On soft-copy displays, 3 masked observers evaluated the detectability of each aperture in each image according to a 5-point scale. The mean sum scores of corresponding images were compared. RESULTS: For all tube voltages and detector entrance doses, the images obtained with the CsI/a-Si detector resulted in better observer contrast-detail performance as compared with the images of the storage phosphor system. The CsI/a-Si system allowed a calculated dose reduction of 39% at 45 kVp, 68% at 70 kVp, and 81% at 113 kVp as compared with the storage phosphor system, without loss of contrast-detail detectability. CONCLUSIONS: Under the conditions of the chosen experimental design, the CsI/a-Si system provided a superior contrast-detail performance as compared with the storage phosphor system. The potential of dose reduction increased with rising tube voltage.

Cesium↗
PubMedDate not supplied

Fatty liver: imaging patterns and pitfalls.

Fat accumulation is one of the most common abnormalities of the liver depicted on cross-sectional images. Common patterns include diffuse fat accumulation, diffuse fat accumulation with focal sparing, and focal fat accumulation in an otherwise normal liver. Unusual patterns that may cause diagnostic confusion by mimicking neoplastic, inflammatory, or vascular conditions include multinodular and perivascular accumulation. All of these patterns involve the heterogeneous or nonuniform distribution of fat. To help prevent diagnostic errors and guide appropriate work-up and management, radiologists should be aware of the different patterns of fat accumulation in the liver, especially as they are depicted at ultrasonography, computed tomography, and magnetic resonance imaging. In addition, knowledge of the risk factors and the pathophysiologic, histologic, and epidemiologic features of fat accumulation may be useful for avoiding diagnostic pitfalls and planning an appropriate work-up in difficult cases.

Diagnosis, Differential↗