Markus Völk

Abdominal MRI after enteroclysis or with oral contrast in patients with suspected or proven Crohn's disease

BACKGROUND & AIMS Diagnostic results of magnetic resonance (MR) enteroclysis correlate highly with those from conventional enteroclysis; nevertheless, intubation of the patient and positioning of an intestinal tube is still necessary for the examination, which is often remembered as the most embarrassing part of the examination by the patient. A more comfortable and highly sensitive examination of the small bowel therefore would increase patient acceptance for recurring examinations, which are often necessary, for example, in patients with Crohns disease. This study evaluates the diagnostic efficacy of abdominal MR imaging (MRI) of the small bowel after drinking contrast agent only compared with conventional enteroclysis and abdominal MRI performed after enteroclysis in patients with suspected or proven Crohns disease. METHODS Twenty-one patients with Crohns disease referred for conventional enteroclysis underwent abdominal MRI after enteroclysis. Additionally, 1 to 3 days before or after these examinations, abdominal MRI was performed using only orally administered contrast. All MRI examinations were performed using a 1.5T scanner. RESULTS All pathological findings on conventional enteroclysis were shown correctly with MRI after enteroclysis and MRI after oral contrast only. Additional information by MRI was obtained in 6 of 21 patients. No statistically significant differences were found in assessing the diagnostic efficacy of the 3 examinations. CONCLUSIONS Abdominal MRI with oral contrast only can be used as a diagnostic tool for evaluation of the small bowel in patients with Crohns disease and has the potential to replace conventional enteroclysis as follow-up.

Comparison of magnetic resonance imaging colonography with conventional colonoscopy for the assessment of intestinal inflammation in patients with inflammatory bowel disease: a feasibility study

Aim: Magnetic resonance imaging (MRI) based colonography represents a new imaging tool which has mainly been investigated for polyp screening. To evaluate this approach for patients with inflammatory bowel disease (IBD), we compared MRI based colonography with conventional colonoscopy for assessing the presence and extent of colonic inflammation. Patients and methods: In 22 consecutive patients with suspected or known IBD, MRI colonography was performed immediately before conventional colonoscopy. After bowel cleansing, a T1 positive contrast agent was applied rectally. In addition to T2 weighted sequences, T1 weighted two dimensional and three dimensional Flash acquisitions as well as volume rendered virtual endoscopy were performed. All images were evaluated with regard to typical MRI features of inflammation. The results were compared with colonoscopy findings. Results: Distension and image quality was assessed as good to fair in 97.4% of all colonic segments. Only four of 154 segments were considered non-diagnostic. With colonoscopy serving as the gold standard, the sensitivity for correctly identifying inflammation on a per segment analysis of the colon was 31.6% for Crohn’s disease (CD) and 58.8% for ulcerative colitis (UC). In CD, in most cases mild inflammation was not diagnosed by MRI while in UC even severe inflammation was not always depicted by MRI. Virtual endoscopy did not add any relevant information. Conclusion: MRI based colonography is not suitable for adequately assessing the extent of colonic inflammation in patients with IBD. Only severe colonic inflammation in patients with CD can be sufficiently visualised.

Dark lumen magnetic resonance enteroclysis in combination with MRI colonography for whole bowel assessment in patients with Crohn's disease: First clinical experience

Background: Magnetic resonance enteroclysis (MRE) is a recently introduced imaging technique that assesses the small bowel with similar sensitivity and specificity as the fluoroscopically performed conventional enteroclysis. Magnetic resonance imaging colonography (MRC) seems to be a promising technique for polyp assessment in the colon. In this feasibility study, we evaluated the combination of small bowel MRI with unprepared MRC as an integrative diagnostic approach of the whole bowel in patients with Crohns disease. Methods: Thirty patients with known Crohns disease were prospectively examined. No particular colonic preparation was applied. Applying the dark lumen technique in all patients, MRE and MRC were performed within 1 session using an integrative examination protocol. T2‐weighted and contrast‐enhanced T1‐weighted sequences were acquired. Inflammation assessment (grades 0 to 2) of the colon was compared with conventional colonoscopy in 29 patient and with surgery in 1 patient. The entire colon was graded fair to good distended in all patients. In 11 of 210 evaluated colonic segments, feces hindered an adequate intraluminal bowel assessment. Twenty‐three of 30 patients had complete colonoscopy as the gold standard. In 7 patients, complete colonoscopy could not be performed because of an inflamed stenosis. Results: Correct grading of colonic inflammation was performed with 55.1% sensitivity and 98.2% specificity in all segments. Considering only more extensive inflammation (grade 2), the sensitivity of MRC increased to 70.2% with a specificity of 99.2%. Conclusions: The combination of MRE and MRC could improve the diagnostic value of abdominal MRI evaluation in patients with Crohns disease. However, MRC can not replace conventional colonoscopy in subtle inflammation assessment.

Detection of Simulated Chest Lesions with Normal and Reduced Radiation Dose: Comparison of Conventional Screen-film Radiography and a Flat-panel X-ray Detector Based on Amorphous Silicon

RATIONALE AND OBJECTIVES The authors compared a solid-state amorphous silicon (a-Si) detector and screen-film radiography (SFR) with regard to the detection of simulated pulmonary lesions. Evaluation of the impact of a dose reduction of 50% with this digital flat-panel detector was of special interest. METHODS A self-scanning flat-panel detector, based on a-Si technology with 143 x 143 microm pixel size, 1 k x 1 k matrix and 12-bit digital output was used. An asymmetric state-of-the-art screen-film system was compared with a-Si images taken at the same dose as SFR-images and at a dose reduced by 50%. An anthropomorphic chest phantom was superimposed by templates containing nodules, linear structures, reticular, and micronodular opacities in a random distribution. Receiver operating characteristic analysis was performed for 23,040 observations made by four independent observers. Students t test (95% confidence-level) was used for statistical analysis. RESULTS Receiver operating characteristic analysis showed that a-Si images taken at the same dose as SFR-images were significantly superior to SFR with respect to the detectability of lines (P = 0.01) and micronodular opacities (P < 0.01). For the other objects and the a-Si images taken at a reduced dose, it yielded no statistically significant differences between both imaging modalities. CONCLUSIONS The results of this phantom study indicate that a-Si detector technology holds promise in terms of dose reduction in chest radiography without loss of diagnostic accuracy compared with SFR.

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.

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 43×43-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.

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 19stenoses 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.

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.Rationale and Objectives.To evaluate the quality of chest radiographs after 32:1 compression/decompression with different image compression algorithms. Methods.Ten digital (Thoravison) radiographs of an anthropomorphic chest phantom with superimposed simulated nodular lesions (NL) and linear reticular lesions (LL) were obtained. Each radiograph was subdivided into 15 fields; they contained the lesions with a probability of 0.5. The radiographs were compressed and decompressed by using JPEG, fractal and wavelet algorithms at a compression rate of 32:1. Five radiologists evaluated the images. Data were analyzed with the receiver operating characteristic (ROC) method (comparison of area under curve). Results.At 32:1 JPEG or wavelet compression, no statistically significant difference was observed for both NL and LL when compared with the original images. The fractal algorithm performed significantly lower for both NL and LL when compared with the original radiographs. Conclusion.The JPEG and wavelet image compression does not result in loss of relevant information for chest x-rays at a compression rate of 32:1.

Amorphous silicon, flat-panel, x-ray detector versus screen-film radiography: effect of dose reduction on the detectability of cortical bone defects and fractures.

RATIONALE AND OBJECTIVES The purpose of this phantom study was to assess the diagnostic performance of a self-scanning, solid-state amorphous silicon (a-Si) detector in skeletal radiography using different exposure parameters. METHODS A flat-panel detector (15 cm x 15 cm), based on a-Si technology with 143 microm x 143 microm pixel size, 1k x 1k matrix, and 12 bit digital output was used. State-of-the-art screen-film radiography (SFR; speed 400, detector dose 2.5 microGy) was compared with a-Si images taken at doses that were equivalent to a speed of 400, 800, 1,250, and 1,600, respectively. A total of 232 segments of long tubular deer-bones (femur, tibia, humerus, radius) had 110 artificial fractures and 112 cortical defects simulating osteolytic lesions. Receiver operating characteristic analysis was performed for 9,280 observations made by four independent observers. Two-tailed Students paired t test was used for statistical analysis (95% confidence level). RESULTS Receiver operating characteristic analysis yielded equivalent results of the a-Si and SFR system. Even at the lowest dose there were no statistically significant differences between both imaging modalities with respect to the detectability of fractures and cortical defects. CONCLUSIONS The results of this study indicate that a-Si detector technology holds promise in terms of dose reduction in skeletal radiography without loss of diagnostic accuracy.

Potential of adipocytokines in predicting peripancreatic necrosis and severity in acute pancreatitis: Pilot study

Background and Aim:  Severe acute pancreatitis is characterized by lipase‐induced peripancreatic fat cell necrosis. Because adipocytes secret several highly active molecules, the aim of the present study was to investigate the hypothesis that adipocytokines could serve as potential markers predicting peripancreatic necrosis and severity in acute pancreatitis.