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A J Aschoff

Publications and source records attributed to A J Aschoff.

At least 37 records · Page 2Linked to original sources
PubMed2001

[Comparison of susceptibility artefacts of different radiofrequency electrodes at O.2 T. Influence of electrode positioning, pulse sequence and image reconstruction methods].

PURPOSE: Interventional MRI procedure monitoring requires small but accurate susceptibility artifacts of the instruments used. In this investigation, susceptibility artifacts of different RF-electrode designs were compared using a variety of pulse sequences and k-space acquisition methods. METHODS: 4 different 18-gauge RF-electrodes (with three single electrodes made of stainless steel, copper, inconal, and a triple-clustered electrode configuration made of inconal) were placed in a 0.2 T MR-scanner perpendicular to the main magnetic field. Pulse sequences used included: TSE T2, FISP, true-FISP, PSIF, and a temperature sensitive ES-GRE sequence. In addition to the 2D Cartesian k-space trajectory with Fourier transformation (2DFT), projection reconstruction (PR) was used with the FISP, true-FISP and PSIF sequences. RESULTS: The best tip accuracy was achieved with the combination of inconal electrodes and TSE T2. The usefulness of the tested sequences was found to be: TSE T2 > PSIF > FISP/true-FISP > ES-GRE. In general 2DFT provided better or equal tip accuracy than PR. The apparent shaft width was smaller using the copper electrode compared to the inconal electrode. However, the "match shaped" tip artifact of the copper probe led to a higher error in tip accuracy. CONCLUSIONS: TSE-T2 sequences and Cartesian 2DFT acquisitions should be used for accurate tip positioning at 0.2 T. Further, artifact size of the electrode shaft prevents the use of inconal for temperature sensitive sequences. Copper electrodes can be used for these purposes, although copper is not considered to be biocompatible at present.

Artifacts↗
PubMed2001

Perfusion-modulated MR imaging-guided radiofrequency ablation of the kidney in a porcine model.

OBJECTIVE: This study was performed to test the hypothesis that temporary renal ischemia will result in increased thermal lesion size during radiofrequency thermal ablation in the kidney. MATERIALS AND METHODS: Twelve kidneys were treated in six pigs that were placed under general anesthesia in the MR suite, using a 0.2-T open C-shaped MR imaging system. A 4-cm-long, 14-mm-diameter balloon catheter was placed into the aorta using a transfemoral approach, and the balloon was positioned proximal to the renal arteries via guidance with MR imaging. A 2-cm exposed-tip MR-compatible 17-gauge radiofrequency electrode was placed into one kidney under MR fluoroscopy using fast imaging with steady-state free precession (FISP) sequences. Thermal ablation was performed with the electrode tip temperature maintained at 90 +/- 2 degrees C for 10 min. This procedure was repeated in the contralateral kidney. The balloon was inflated during one ablation. Postablation images were obtained, the pigs were sacrificed, and both kidneys of each animal were harvested for pathologic correlation. RESULTS: Technical success was achieved in all animals. The lesion measured 14.2 +/- 2.2 mm (mean +/- standard deviation) for the ischemic kidney versus 8.0 +/- 2.6 mm in the normally perfused kidney (p = 0.00002). No significant complications were noted. In all images, thermal lesions displayed low signal intensity with a sharp rim of high signal intensity best visualized using short tau inversion recovery (STIR) sequences with a mean accuracy of 1.3 +/- 1.2 mm when compared with pathologic findings and a mean contrast-to-noise ratio of 4.9 +/- 2.5. CONCLUSION: We accept the hypothesis that temporary renal ischemia leads to a significantly increased radiofrequency ablation lesion size. We conclude that catheter-based balloon perfusion reduction is feasible, that the procedure does not lead to major complications, and that it can be performed using MR imaging as the sole imaging modality.

Animals↗
PubMed2000

Thermal lesion conspicuity following interstitial radiofrequency thermal tumor ablation in humans: a comparison of STIR, turbo spin-echo T2-weighted, and contrast-enhanced T1-weighted MR images at 0.2 T.

The purpose of this study was to compare the contrast between radiofrequency (RF) thermal liver lesions and surrounding tissue in T2-weighted turbo spin-echo sequences (TSE T2), short TI inversion recovery techniques (STIR), and contrast-enhanced (CE) T1-weighted spin-echo images. Nineteen RF thermal ablations were performed on eight patients with metastatic liver tumors. After ablation, contrast-to-noise ratios (CNRs) were calculated between mean signal amplitudes from three regions of interest (ROI) (lesion, surrounding edema, and normal tissue) using TSE T2-weighted, STIR, and contrast-enhanced T1-weighted (CE T1) sequences for each lesion. CNRs between the thermal lesion and normal liver tissue for both TSE T2-weighted (mean 0.9) and STIR (2.0) images were significantly lower than for CE T1-weighted (8.4) images (t-test, alpha = 0.05). However, CNRs between edema rim and the core of the thermal lesion for both TSE T2-weighted (8.1) and STIR images (7.2) were not significantly different (t-test, alpha = 0.05) from CNRs between lesion and normal tissue for CE T1-weighted images (8.4), nor was the CNR between edema rim and normal tissue for both TSE T2-weighted (10.3) and STIR (9.8) images. Although the edema was not visible on CE T1-weighted images, 18 of 19 lesions (94.7%) were surrounded by a hyperintense rim on TSE T2-weighted or STIR images. Both TSE T2-weighted and STIR sequences represent valid techniques for repeatable assessment of RF thermal lesions.

Adult↗
PubMed2000

Active MR guidance of interventional devices with target-navigation.

This project incorporated a novel inductive coupling structure of three micro coils into an invasive device tip to determine both its tip position and orientation. Moreover, with the introduction of a new target-navigation technique the MR scan plane was defined automatically by the invasive device orientation and target tissue location. A time domain multiplexing technique was applied for simultaneous MR imaging and device tracking. Using these techniques, the acquired MR images always showed both the invasive device and its target tissue. Thus, roadmap images and their potential misregistration errors were avoided. A graphical user interface (GUI) was also designed to assist interventional physicians in monitoring and guiding the insertion of the interventional device. Ex vivo phantom and in vivo animal experiments were performed to test this new technique. The methods developed in this project provide a new active technique for interventional device guidance using MRI. Magn Reson Med 44:56-65, 2000.

Animals↗
PubMed2000

Diagnosis of papillomas of the breast: value of magnetic resonance mammography in comparison with galactography.

The aim of this study was evaluation of MRI alone and in combination with mammography and galactography in the diagnosis of intraductal papillomas. From 1994 to 1998, a total of 48 women presenting with pathologic mammary secretion underwent galactography and magnetic resonance mammography (MRM). Thirty-five patients aged 16-71 years (average age 46 years) subsequently underwent surgery or diagnostic puncture and the histologic findings were compared with the results of the radiologic examination. Histology revealed papillomas in 16 cases. In 6 of these patients, there was associated malignant degeneration. Malignancy without associated papilloma was observed in 3 cases. Galactography displayed a sensitivity of 94% and a specificity of 79% with five false-positive findings and one false-negative finding in the recognition of intraductal papillomas. Malignant processes were detected by mammography/galactography in only one instance. Magnetic resonance mammography visualized pathologic contrast medium uptake in 8 of 9 cases of malignant disease (sensitivity 89%). One patient with in situ ductal carcinoma escaped detection with MRM. Papillomas showed no or below-the-threshold-lying contrast uptakes with no specific sign suggestive of papilloma. Galactography in combination with mammography remains the primary diagnostic procedure in cases of pathologic mammary secretion or suspected papilloma. The addition of MRI permits exclusion of malignant disease with a high degree of certainty; thus, expectant management in individual cases with negative findings appears justified.

Breast↗
PubMed2000

Embolization for gastrointestinal hemorrhages.

Retrospective evaluation of interventional embolization therapy in the treatment of gastrointestinal hemorrhage over a long-term observation period from 1989 to 1997. Included in the study were 35 patients (age range 18-89 years) with gastrointestinal bleeding (GI) referred for radiological intervention either primarily or following unsuccessful endoscopy or surgery. Sources of GI bleeding included gastric and duodenal ulcers (n = 7), diverticula (n = 3), erosion of the intestinal wall secondary to malignancy (n = 6), vascular malformations (n = 4), and hemorrhoids (n = 2), as well as from postoperative (n = 6), posttraumatic (n = 2), postinflammatory (n = 4) or unknown (n = 1) causes. Ethibloc (12 cases) or metal coils (14 cases) were predominantly used as embolisates. In addition, combinations of tissue adhesive and gelfoam particles and of coils and Ethibloc were used (six cases). Finally, polyvinyl alcohol particles, a coated stent, and an arterial wire dissection were utilized in one case each. Bleeding was stopped completely in 29 of 35 cases (83%). In one case (3%) the source of bleeding was recognized but the corresponding vessel could not be catheterized. In five other cases (14%) there was partial success with reduced, though still persistent, bleeding. The rate of complications was 14%, including four instances of intestinal ischemia with fatal outcome in the first years, and, later, one partial infarction of the spleen without serious consequences. Gastrointestinal hemorrhage can be controlled in a high percentage of patients, including the seriously ill and those who had previously undergone surgery, with the use of minimally invasive interventional techniques. The availability of minicoils instead of fluid embolization agents has reduced the risk of serious complications.

Adolescent↗
PubMed2000

Percutaneous magnetic resonance image-guided biopsy and aspiration in the head and neck.

OBJECTIVE/HYPOTHESIS: To test the hypotheses that 1) magnetic resonance imaging (MRI)-guided biopsy and aspiration with an open 0.2-T system (Magnetom Open, Siemens, Erlangen, Germany) in the head and neck is feasible and successful and 2) procedure times can be sufficiently short to be well tolerated by the patient. METHODS: Sixty-one MRI-guided procedures were performed in 47 patients (ages, 6 mo-88 y) in the head and neck, including the mucosal sites and masticator and parapharyngeal spaces (n = 23), parotid space (n = 6), submandibular space (n = 2), cervical vertebral column/paraspinal tissues (n = 8), skull base (n = 3), larynx or hypopharynx (n = 3), and infrahyoid nodal chains and surrounding tissues (n = 16). A clinical C-arm imaging system was used, supplemented by an in-room radiofrequency-shielded liquid crystal monitor, rapid gradient echo sequences for needle guidance, and MRI-compatible anesthesia, monitoring, and surgical lighting equipment. Tissue sampling included fine-needle aspiration (n = 58) and cutting-needle core biopsy (n = 27), with 24 patients undergoing both procedures. Procedures were evaluated for success of needle placement, procedure time, and complications. RESULTS: Successful needle placement was accomplished in all cases without complication, with tissue sufficient for pathological diagnosis obtained for all but five patients with an average of 2.1 passes per patient. For fine-needle aspiration, average instrument time was 7.8 minutes per pass, and average cutting-needle core biopsy time was 9.2 minutes. CONCLUSIONS: Interactive MRI guidance for needle biopsy and aspiration of deep head and neck lesions is feasible, successful, and safe. Procedure times are sufficiently short to be well tolerated by the patient.

Adolescent↗
PubMed1999

[Interventional treatment of hemorrhages in advanced cervical carcinoma].

PURPOSE: Retrospective evaluation of percutaneous interventional treatment of locally advanced cervical carcinoma. MATERIALS AND METHODS: Since 1991, 13 patients with advanced tumor disease have been referred to our department for diagnosis and therapy of an acute blood loss. In all patients (age 40-88 years, mean 61 years) hemorrhage was detected by decrease in red blood cell count. In all cases patients suffered from locally advanced or recurrent disease after surgery and/or additional radio- or chemotherapy. Embolization was performed by transfemoral access using minicoils in most cases, liquid agents less often and a covered vascular stent in one patient. RESULTS: The site of the hemorrhage or the blood pooling of the tumor could be seen in all cases angiographically. Twenty-seven treatment cycles (2.1 per patient) were performed at intervals of 3 days to 6 months. The maximum time of follow-up and additional treatments if necessary was 1 year. In 9 of 13 patients (69%) the bleeding could be stopped immediately with a single treatment or initial treatment via both iliac arteries. One patient (7,7%) died during therapy because of an uncontrollable bleeding and consecutive decrease in red blood cells count. The remaining three patients (23%) showed slight persistent or recurrent bleeding, which could be managed interventionally until the following episode. There were two complications (15%) during therapy, representing a coil misplacement and a coil wash-out, which both could be managed interventionally. CONCLUSION: Hemorrhage following locally advanced or recurrent cervical carcinoma can be stopped interventionally in about 70% of cases. Even in partial success it is possible to manage the acute life-threatening situation. Follow-up examinations of up to 1 year justify this therapeutic concept.

Adult↗
PubMed1999

Pancreas: does hyoscyamine butylbromide increase the diagnostic value of helical CT?

Among 50 patients referred for helical computed tomography (CT) of the pancreas, 24 randomly selected patients received 40 mg of hyoscyamine butylbromide to evaluate whether its administration improved image quality and diagnostic findings. Differences between the groups were not statistically significant. It was therefore concluded that hyoscyamine butylbromide does not contribute a diagnostic advantage at helical CT of the pancreas.

Adult↗
PubMed1998

[MRI of the abdomen combined with enteroclysis in Crohn disease using oral and intravenous Gd-DTPA].

In spite of the improved MR-diagnosis of the abdomen, MRI is not used as a routine method for the diagnosis of inflammatory small bowel disease. The aim of this study was--after optimazation of the bowel opacification--the correlation of the findings obtained with enteroclysis and MRI in patients with known Crohns' disease. 60 patients between 17 and 72 years of age were investigated. First, an enteroclysis was performed in typical manner. The applicated methylcellulosis was blended with positive oral MR contrast media (Magnevist oral, Schering). After enteroclysis, MRI of the abdomen was performed using T1- and T2-weighted breathhold sequences (Flash 2D pre- and postcontrast and TSE) in axial and coronal planes. The length of the affected bowel and the stenosis seen with enteroclysis correlated well with the visible thickening of the small bowel wall and the stenosis seen in MRI. Using MRI, additional findings could be obtained in 28 patients, such as fistulas, abscesses or a hydronephrosis, or a better assessment of the stenosis was possible with MRI, because of the avoidance of overshadowing of the affected bowel loop with MRI. A brilliant MR-tomographic imaging of the small bowel is possible under the condition, that the small bowel contrast is optimal. The main prerequisite is a large filling volume of the small bowel to reach a homogeneous contrast and a good distension of the small bowel lumen.

Administration, Oral↗
PubMed1998

[High-resolution virtual laryngoscopy based on spiral CT data].

This pilot study investigated the feasibility and clinical value of high-resolution virtual real-time laryngoscopy based on helical CT data sets. Nine patients with laryngeal pathology (three with tumors of the vocal cords, two laryngeal carcinomas, one with invasion of the larynx by thyroid carcinoma and six subglottic stenoses) underwent examination by helical CT at a collimation of 1 mm. Following acquisition, the images were processed at a workstation with standard visualization software, such that virtual endoscopy (VE) in real time was possible. The images were then compared with the findings of conventional endoscopy. Because of swallowing artifacts, reconstruction failed in 2 of 12 patients. None of the carcinomas of the vocal cords was recognized at VE or in the cross-sectional CT images. VE provided the correct diagnosis in 8 of 12 cases (laryngeal tumors, subglottic stenoses). Virtual laryngoscopy is capable of simulating the visual findings of endoscopy in cases of laryngeal tumors and subglottic stenoses. Small tumors of the vocal cords are not adequately visualized. The major problem affecting results is motion artifacts resulting from involuntary swallowing.

Aged↗
PubMed1998

MRI follow-up of pisiform bone transposition for treatment of lunatomalacia.

OBJECTIVE: Transposition of the pisiform bone is an operative treatment for lunatomalacia. The postoperative viability of the transposed pisiform bone is difficult to assess. The purpose of the study was to evaluate the utility of MRI for postoperative assessment of viability of the pisiform and lunate bones. DESIGN AND PATIENTS: Six patients who underwent transposition of the pisiform for treatment of lunatomalacia, were assessed pre- and postoperatively with conventional radiographs (including tomography), CT and MRI. RESULTS: Conventional radiographs, conventional tomograms and CT were all useful in demonstrating the location of the transposed pisiform. CT showed the transposed pisiform without superposition. However, neither CT nor conventional techniques provided information regarding viability of the pisiform. In all patients investigated in the first year following surgery, T1-weighted MR images showed high signal intensity in the transposed bones. In all patients investigated after 1 year, the signal intensity decreased to an intermediate level on T1-weighted images. Enhancement following contrast medium administration in the transposed pisiform and the lunate was noted in all patients, indicative of viability. CONCLUSION: Contrast-enhanced MRI is able to provide important information regarding the viability of the transposed pisiform and the remaining parts of the lunate. Thus, contrast-enhanced MRI provides an improved means of postoperative assessment regarding short-term follow-up following pisiform transposition. In the long-term follow-up conventional radiography and CT may be equal to MRI in showing increasing sclerosis and/or fragmentation.

Adolescent↗
PubMed1998

[The percutaneous transarterial embolization therapy of traumatic kidney hemorrhages].

PURPOSE: To demonstrate the possibility of transarterial, superselective embolization after traumatic kidney injury and hemorrhage in patients usually treated by surgery. METHODS: In a series of 16 patients aged 21 to 86 years (mean 37 years) external trauma led to kidney damage and consecutive bleeding. After diagnostic angiography (5 F) the exact site of hemorrhage was detected and treated by superselective embolization via a coaxial catheter system (2.7 F) either by coils (n = 5) or liquid agents (ethibloc, n = 11). RESULTS: In all patients bleeding was stopped interventionally. Additional surgical treatment was not necessary in any case. In one older patient with preinterventionally known reduced kidney function, the excretion function decreased to creatinine levels of about 3.6 mg/dl after therapy and led to compensated nephric insufficiency. Other complications were not observed. CONCLUSION: Interventional embolization is a well-tolerated and effective treatment modality after traumatic kidney hemorrhage. After exclusion of other injuries obligate for surgery, percutaneous transarterial therapy may help to avoid an operation. This reduces the risk of narcosis and treatment especially in multimorbid patients.

Adult↗
PubMed1998

Diagnostic value of spiral-CT angiography in comparison with digital subtraction angiography before and after peripheral vascular intervention.

To evaluate spiral-computed tomography (CT) angiography in primary diagnosis and/or in noninvasive follow-up after vascular intervention, we compared spiral-CT angiography and conventional angiography before and after vascular intervention. Helical-CT examinations before and after percutaneous transluminal angioplasty (PTA) or stent implantation were performed in 10 patients (mean age 63 years) with symptomatic peripheral arteriosclerotic disease. Stenoses were located in the iliac, femoral, or popliteal artery. CT examinations were done with a spiral-CT in double detector technique (CT Twin, Elscint). The parameters were as follows: slice thickness: 5.5 mm, increment: 2.7 mm, pitch: 1.5, contrast medium: 150 mL, flow rate: 2.5 mL/second, delay: 30 seconds. For evaluation, transverse planes as well as maximum intensity projections and 3-D reconstructions were used. The possible scan length reached from the aortic bifurcation down to about 10 cm below the ankle trifurcation. Preinterventional digital subtraction angiography (DSA) was superior to CT angiography (CTA: 94%, maximum intensity projection [MIP] alone: 65%), although high-grade stenoses were detected by both methods. After intervention, a resolved stenosis and improved peripheral flow could be detected by helical-CT as well as by intraarterial angiography in every patient (100%). In the primary diagnosis of vascular changes, intraarterial DSA remains the method of choice. Nevertheless, spiral-CT angiography shows comparable results after percutaneous intervention and becomes a noninvasive alternative in the postinterventional follow-up.

Angiography↗
PubMed1998

The average dose-area product at intravenous urography in 205 adults.

The intravenous urography (IVU) is the most important and most frequently performed radiological examination in urology. This prospective study determined the dose-area product as a measurement of radiation dose in 205 adult patients undergoing IVU. Average dose-area product was 1017 cGy cm2. An average 3.7 radiographs were obtained per patient. Tomographic views were required in only 8.8% of cases. Radiation dose is dependent not only on the number and size of the obtained radiographs, but on the physical constitution of the patient. The dose-area products measured show a clear relationship to the body weight of the patient.

Adolescent↗
PubMed1998

Virtual cystoscopy based on helical CT scan datasets: perspectives and limitations.

The purpose of the study was to simulate cystoscopy based on three-dimensional helical CT scan datasets in real-time in patients with tumours of the urinary bladder. A helical CT scan with double detector technology was carried out pre-operatively in 11 patients with histologically confirmed carcinoma of the urinary bladder and one patient with chronic cystitis. A non-enhanced scan was first performed, followed by an examination in the early phase of contrast medium enhancement. Further images were acquired after adequate filling of the bladder with contrast medium, approximately 30 min after injection. These data were transferred to a separate graphic computer workstation and reconstructed. The results were then compared with the cystoscopic and histopathological findings. All tumours of the urinary bladder identified at fibreoptic cystoscopy were shown on virtual cystoscopy. The best reconstruction results were obtained from data acquired 30 min after injection of contrast medium. The ureteric orifices were not visualized at virtual cystoscopy. These data lead us to conclude that, at present, virtual cystoscopy has not reached the quality of fibreoptic examination and remains restricted to use in specific cases, for example patients with urethral strictures.

Aged↗