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Elmar M Merkle

Publications and source records attributed to Elmar M Merkle.

33 records · Page 2Linked to original sources
PubMed2004

Low-flow vascular malformations: MR-guided percutaneous sclerotherapy in qualitative and quantitative assessment of therapy and outcome.

PURPOSE: To prospectively assess the therapeutic procedure and outcome of magnetic resonance (MR)-guided percutaneous sclerotherapy in patients with low-flow vascular malformations. MATERIALS AND METHODS: Seventy-six percutaneous sclerotherapy treatments were performed by one radiologist with real-time MR guidance in 15 patients (six female patients; mean age, 54.4 years +/- 11.1; nine male patients; mean age, 32.9 years +/- 14.1) with vascular malformations in the head and neck (n = 64), spine (n = 5), and extremities (n = 7). Qualitative assessment was used to analyze (a) individual success of therapy, (b) occurrence of complications, (c) time required for minimally invasive MR-guided sclerotherapy in regression analysis, (d) ability of MR imaging to depict postinterventional perfusion changes within the vascular malformation with calculation of changes in contrast-to-noise ratios, and (e) detection of volume changes at follow-up examinations with volumetric analysis. RESULTS: Percutaneous sclerotherapy was performed successfully and without complications by filling targeted vascular malformations with sclerosing agent. Induced vascular sclerosis was used to successfully treat individual predominant symptoms, such as hemorrhage, pain, cosmetic disfigurement, and functional impairment. Quantitative analysis focusing on the actual interventional length of time presented an acceleration over the 5-year time period, matching a cubic function in regression curve fit and taking 31 minutes 50 seconds +/- 14 minutes. Induced vascular thrombosis was identified in all treated portions on postinterventional images by the statistically significant changes in contrast-to-noise ratio (P < .05) compared with preinterventional imaging. On follow-up images (ie, those obtained after 12 weeks +/- 6), shrinkage was observed in targeted portions (67.2% +/- 18.9). CONCLUSION: MR imaging allows safe guidance and monitoring of minimally invasive sclerotherapy and permits verification of therapeutic success postinterventionally and during follow-up examinations.

Adolescent↗
PubMed2004

Multidetector CT angiography of arterial inflow and runoff in the lower extremities: a challenge in data acquisition and evaluation.

PURPOSE: To show the feasibility of acquiring homogenous 3-dimensional datasets with high temporal and spatial resolution from computed tomographic angiographic (CTA) scans of the lower extremities and to assess automated vessel-tracking techniques for vascular evaluation. METHODS: Eighteen men (mean age 67.0 years, range 43-83) with aneurysmal or occlusive vascular diseases underwent contrast-enhanced CTA of the lower limb arteries utilizing a 16-row CT imager. Curved multiplanar reformations were generated by manual selection of vessel centerlines in the infrarenal aorta and the arterial vasculature in the pelvis, thigh, and calf based on volume-rendering techniques. For each vessel, opacification and depiction were quantitatively evaluated. The manually segmented images were compared to datasets processed with automated vessel-tracking strategies by 5 radiologists, who evaluated diagnostic reliability and image quality. A Differential Receiver Operating Characteristic (DROC) analysis was performed. RESULTS: An increase in the temporal and spatial resolution led to acquisition of high quality CTA datasets. Significant homogeneity of the vascular contrast-to-noise ratios was achieved in the pelvic (coefficient of variance 1.5% to 10.1%), thigh (0.1% to 9.4%), and calf (3.3% to 19.2%) vessels. The assessment of vascular delineation revealed full-width-at-half-maximum contrast values of 96.4%, 95.5%, and 111.3% in the pelvis, thigh, and calf, respectively. Observers were not able to distinguish between manual and automated vascular segmentation, as represented by a 0.56 value for the area under the DROC curve. CONCLUSIONS: High-resolution CTA lower extremity datasets were acquired successfully, presenting vascular signal intensities of high homogeneity suitable for automated vessel-tracking techniques. Automated 3D visualization tools produced reliable, reproducible, and time-efficient centerline extractions that were comparable to manually defined centerlines.

Adult↗
PubMed2003

Differentiating a chronic hyperplastic mass from pancreatic cancer: a challenge remaining in multidetector CT of the pancreas.

A multitude of clinical symptoms originate from pancreatic inflammatory or neoplastic processes due to their highly complex composition, function, and anatomic relationships to adjacent organs as well as the heterogeneous patterns of vascular perfusion and neural innervation of the pancreatic gland which complicate an early and precise diagnosis. Whereas early assessment of inflammatory or neoplastic pancreatic processes is a prerequisite for a successful curative approach, the classical radiologic signs of chronic pancreatitis and pancreatic carcinoma show significant similarities. This article provides an overview of the pathogenesis and imaging findings in chronic pancreatitis and pancreatic cancer, including some new approaches for visualizing the subtle but distinct differences between these two entities.

Adenocarcinoma↗
PubMed2003

Multislice helical CT of the pancreas and spleen.

Multislice helical CT (MSCT) with its multidetector technology and faster rotation times, has led to new dimensions in spatial and temporal resolution in CT imaging. In contrast to single-slice CT, smaller slice collimations can be applied that lead to almost isotropic voxels and allow high quality multiplanar and 3-D image reconstructions. The high speed of multislice CT can be used to reduce the time needed to cover a given volume, to increase the spatial resolution along the z-axis by applying thinner slice collimations, and to cover longer anatomic volumes. The speed of MSCT allows organ imaging in clearly defined perfusion phases, e.g. the arterial, parenchymal, and portal venous perfusion phases. Contrast agents with higher iodine concentrations (400 mg iodine per ml compared with 300 mg iodine per ml) lead to higher contrast enhancement of the pancreas (arterial+portal venous phases), the kidneys (arterial+portal venous phases), the spleen (arterial phase), the wall of the small intestine (arterial+portal venous phases), the larger and smaller arteries (arterial phase), and the portal vein (portal venous phase). All of these advancements lead to improved visualization of small structures and of various pathologies, such as pancreatic tumors, liver metastases, vessel infiltration, and vascular diseases.

Humans↗
PubMed2003

Do surgical clips interfere with radiofrequency thermal ablation?

OBJECTIVE: This study sought to evaluate whether surgical clips affect tissue conductivity and thereby alter the induction of radiofrequency ablation lesions and to determine whether therapy is safe after previous placement of clips in the liver. MATERIALS AND METHODS: An ex vivo porcine hepatic model was used. Three clips were placed around a radiofrequency electrode at 10, 20, and 30 mm from the point of insertion. Clips were arranged in a plane either perpendicular or parallel to the electrode track. After placement of the liver specimen on a grounding pad, radiofrequency energy was applied in a standardized manner for 5 min. Lesion growth and morphology were documented for each minute. RESULTS: Radiofrequency lesions appeared circular and homogeneous after 5 min. Lesion diameter perpendicular to the radiofrequency electrode averaged 30 mm. However, lesion formation was irregular during the early phase of the radiofrequency ablation. The lesion extended irregularly toward the 1-cm clip after 60 sec of ablation. During the second minute, a distinct lesion was observed around the clip 1 cm from the electrode; the primary lesion had not yet reached the clip. During the final 3 min, the primary lesion reached the 1-cm clip and ultimately incorporated the satellite lesion. No lesions were detected surrounding the more distant clips. CONCLUSION: Our data suggest that with the parameters applied in our study, radiofrequency ablation can be safely performed in patients with implanted clips. No aberrant conduction is observed around surgical clips that are located 20 mm and further from the radiofrequency electrode.

Animals↗
PubMed2002

Imaging of acute pancreatitis.

Acute pancreatitis is defined as an acute inflammatory process of the pancreas with variable involvement of peripancreatic tissues or remote organ systems. This article reports the current classification, definition and terminology, epidemiology and etiology, pathogenesis and pathological findings, clinical and laboratory findings, and finally imaging findings of acute pancreatitis with emphasis on cross-sectional imaging modalities such as ultrasound, computed tomography, and magnetic resonance imaging.

Acute Disease↗
PubMed2002

Femur: MR imaging-guided radio-frequency ablation in a porcine model-feasibility study.

PURPOSE: To determine the feasibility of magnetic resonance (MR) imaging-guided and -monitored radio-frequency (RF) ablation of bone. MATERIALS AND METHODS: Seven femurs were treated in five pigs with use of a 0.2-T open MR imager. An 11-gauge bone marrow needle was percutaneously inserted into the distal femur metaphysis with MR fluoroscopy (fast imaging with steady-state precession, or FISP, sequences) to introduce an RF electrode into the bone with further image guidance. Thermal ablation was performed for 10 minutes (90 degrees C +/- 2 [mean +/- SD]). MR follow-up was performed immediately after ablation and again at 7 and 14 days after the procedure (with contrast material-enhanced T1-weighted, T2-weighted, and fast short inversion time inversion-recovery, or STIR, sequences). The animals were sacrificed at day 14. The femurs were sliced, decalcified, and stained. Image analysis was performed to measure lesion diameter and contrast-to-noise ratio (CNR) and to evaluate complications. RESULTS: Technical success was obtained in all animals. The lesion diameter perpendicular to the electrode was 15.4 mm +/- 2.7. No significant complications were noted. The thermal lesions displayed low signal intensity with a sharp rim of high signal intensity. T2-weighted images demonstrated the highest CNR and the lowest error in predicting the lesion size immediately after ablation (2.7 mm +/- 1.3). Contrast-enhanced T1-weighted images demonstrated the highest accuracy at day 14 (1.0 mm +/- 1.0). CONCLUSION: RF ablation of bone with MR imaging as the sole imaging modality is feasible and allows monitoring of the ablation.

Animals↗
PubMed2002

Endovascular treatment of visceral artery aneurysms.

PURPOSE: To review a 10-year experience with endovascular embolization of visceral artery aneurysms. METHODS: Twenty-five patients (13 men; mean age 52.1 years, range 31-80) presented with VAAs of varying locations and etiologies: 10 splenic, 3 gastroduodenal, 2 pancreaticoduodenal, 3 hepatic, 3 superior mesenteric, 2 celiac, 1 left gastric, and 1 jejunoileal. Ten patients were asymptomatic; 7 aneurysms were ruptured. Transcatheter coil embolization was the treatment of choice in all patients. RESULTS: Coil placement was initially (<7 days) successful in 23 (92%) patients. One superior mesenteric artery aneurysm remained perfused, and recurrent bleeding occurred 2 days after intervention in 1 case, but repeated embolization excluded the aneurysm. One patient with necrotizing pancreatitis died from sepsis 10 days after endovascular treatment and surgery (4% 30-day mortality). Long-term follow-up revealed excellent results after an average 48.7 months (range 14-75) with only 1 recurrence after 12 months. CONCLUSIONS: Embolotherapy is the treatment of choice in visceral artery aneurysms, regardless of etiology, location, or clinical presentation.

Adult↗
PubMed2002

Contrast-enhanced 3D MRA of the aortoiliac and infrainguinal arteries when conventional transfemoral arteriography is not feasible.

PURPOSE: To evaluate whether contrast-enhanced 3-dimensional (3D) magnetic resonance angiography (MRA) can substitute for transaxillary or transbrachial catheter access when angiography via the transfemoral route is not possible. METHODS: Contrast-enhanced 3D MRA was performed in 14 patients (12 men; mean 66.1 +/- 12.4 years, range 48-98) with atherosclerotic disease of the aorta or lower extremities in whom conventional transfemoral arteriography was not feasible. The images were evaluated for their ability to identify and characterize lesions directly responsible for the patient's symptoms, adequately depict the vascular anatomy for therapy planning, and identify additional lesions not directly responsible for the patient's symptoms. The arterial system was divided into 15 segments, and image quality and the presence of occlusive disease were determined. RESULTS: MRA adequately depicted 387 (95%) of 406 arterial segments in 14 patients. Nineteen (5%) arterial segments were inadequately delineated because of low signal intensity distal from severe stenoses (n = 11), venous overlap (n = 6), or metallic clip-induced signal voids (n = 2). The lesions directly responsible for the patients' symptoms were identified in all 14 patients (2 aortic occlusions [Leriche's syndrome] and 12 iliac occlusions or severe stenoses). Visualization of the vascular anatomy was adequate for therapy planning in 13 of 14 patients, and 3D MRA satisfactorily identified other lesions not directly responsible for the current symptoms. CONCLUSIONS: When transfemoral catheter angiography of the aortoiliac and lower extremities is not feasible, contrast-enhanced 3D MRA is suitable for determining and planning therapy and can be used instead of angiography via the transaxillary or transbrachial routes.

Aged↗
PubMed2002

Magnetic resonance imaging versus multislice computed tomography of thoracic aortic endografts.

PURPOSE: To compare the potential of magnetic resonance imaging (MRI) to multislice computed tomography (CT) for evaluating stent-graft placement in the thoracic aorta. METHODS: Susceptibility artifacts in 2 different stent-graft systems (Talent and Excluder) were evaluated in vitro in 2 angulations (straight and 33 degrees curved) using 3 different MRI gradient echo sequences (True FISP, 2-dimensional FLASH, and 3-dimensional Turbo FLASH). The size of the stent-related artifact was measured, and the relative stent lumen was calculated. In vivo stent demarcation, stent patency, and additional findings were determined in 13 patients (3 Talent, 9 Excluder, and 1 combined) and compared to CT findings. RESULTS: In vitro, both endograft systems proved to be MR compatible, with the relative stent lumen value ranging from 82% to 100% in the straight configuration; in a curved model, the relative stent lumen value ranged from 56% to 92% with the 3D Turbo FLASH sequence, which provided the smallest susceptibility artifacts. The Excluder endoprosthesis caused significant signal inhomogeneity within the stent in a curved configuration. In vivo, MRI and multislice CT showed similar results, with CT imaging slightly superior in stent demarcation and MRI better in demonstrating thrombus. CT beam hardening artifacts were pronounced in the Talent system, while the Excluder device caused significant signal inhomogeneity within the stent on magnetic resonance angiography. CONCLUSIONS: Multislice CT and contrast-enhanced MRI are fast, reliable means of providing all relevant information for surveillance of fully MR-compatible stent-grafts in the thoracic aorta.

Aorta, Thoracic↗
PubMedDate not supplied

Helical computed tomography of the pancreas: potential impact of higher concentrated contrast agents and multidetector technology.

The introduction of multidetector helical computed tomography (CT) has revolutionized the field of pancreatic imaging and has created a new dimension of temporal and spatial resolution. The speed of multidetector CT can either be used to reduce the time needed to cover a given volume or to increase the resolution along the z-axis, thereby resulting in nearly isotropic voxels. Pancreatic perfusion phases can thus be more clearly differentiated and small structures are better delineated, leading to an improvement in the diagnostic value of pancreatic CT. Contrast media with a higher iodine concentration seem to be superior to lower concentrated contrast agents, mainly because of the better evaluability of the vessels in the arterial examination phase. This manuscript reports current CT imaging strategies for patients with pancreatic cancer with emphasis on vascular invasion, lymph node metastasis, liver metastasis, and peritoneal carcinomatosis.

Contrast Media↗
PubMedDate not supplied

Assessment of automatic vessel tracking techniques in preoperative planning of transluminal aortic stent graft implantation.

OBJECTIVE: To evaluate automatic vessel tracking techniques in the course of preoperative planning prior to transluminal aortic endograft implantation by comparing accuracy, reproducibility, and postprocessing time with source image and volume-rendered analysis methods. METHODS: Multislice computed tomography datasets of 5 patients with abdominal aortic aneurysms were preoperatively examined, performing volumetric analysis of diameter and position of renal artery orifices, aneurysmal neck, maximal aneurysmal extension, aortic bifurcation, and iliac arteries and bifurcation. Analysis was realized by utilizing transverse datasets, volume rendering, and automated vessel tracking strategies (MxView, Philips, Best, The Netherlands). Measurement techniques were evaluated by 2 independent readers 3 times for each patient and measurement modality. Statistical analysis evaluated accuracy of the measurements and intra- and interobserver reliability. Postprocessing time was documented. RESULTS: Using transverse source datasets, intraobserver reliability ranged from 0.49 to 0.58. Intraobserver reliability improved to 0.7 to 0.98 when volume-rendered datasets were evaluated. Interobserver variability for transverse and volume-rendered datasets ranged from 0.49 to 0.76 and 0.70 to 0.96, respectively. Automated vessel tracking datasets did not demonstrate any intra- or interobserver variability. Based on transverse datasets, the length and diameter of iliac arteries and location and diameter of the aneurysmal neck were measured as statistically different in all cases in contrast to volume rendering and automated segmentation techniques. Postprocessing time consumption for measurements based on transverse, volume-rendered, and automated tracking segmentation datasets averaged 3.32 minutes, 25.43 minutes, and 2.24 minutes, respectively. CONCLUSIONS: Preoperative measurements improve significantly if datasets are evaluated based on volume-rendering techniques. This time-consuming procedure can be shortened, while further reducing observer variability, with automatic segmentation techniques.

Aged↗
PubMedDate not supplied

Dual gradient-echo in-phase and opposed-phase hepatic MR imaging: a useful tool for evaluating more than fatty infiltration or fatty sparing.

A T1-weighted gradient-echo in-phase and opposed-phase sequence has become a routine part of every hepatic magnetic resonance (MR) imaging protocol. Although this sequence is primarily used to identify common pathologic conditions, such as diffuse or focal steatosis and focal fatty sparing, it is also helpful in detection of pathologic entities associated with T2* effects owing to the double-echo approach. Thus, pathologic conditions such as hemochromatosis or hemosiderosis can be identified and characterized with a high level of confidence. In cases of iron storage disease, the hepatic parenchymal signal intensity decreases on the image with the longer echo time due to the continued decay of the transverse magnetization. In addition, susceptibility artifacts can be easily detected and characterized with in-phase and opposed-phase MR imaging. Metallic objects demonstrate a larger susceptibility artifact on the image with the second or longer echo time, which is usually the in-phase image. Finally, intrahepatic pneumobilia can be identified with the T1-weighted gradient-echo in-phase and opposed-phase sequence because gas also causes a susceptibility artifact, which is more pronounced on the image with the longer echo time. A complete understanding of both the chemical shift cancellation artifact and the T2* effects of the in-phase and opposed-phase sequence is important for correct interpretation of hepatic MR images.

Diagnosis, Differential↗