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Biomedical subjects

E M Merkle

Publications and source records attributed to E M Merkle.

At least 37 records · Page 2Linked to original sources
PubMed1998

[Pulse sequences and visualization of instruments].

While initially advocated primarily for intrasurgical visualization (e.g., craniotomy), interventional MRI rapidly evolved into roles in image-guided localization for needle-based procedures, and thermal ablation of cancer. In this contest, MRI pulse sequences and scanning methods serve one of four primary roles: (1) speed improvement, (2) device localization, (3) anatomy/lesion differentiation and (4) temperature sensitivity. The first part of this manuscript deals with passive visualization of MR-compatible needles and the effects of field strength, sequence design, and orientation of the needle relative to the static magnetic field of the scanner. Issues and recommendations are given for low-field as well as high-field scanners. The second part contains methods reported to achieve improved acquisition efficiency over conventional phase encoding (wavelets, locally focused imaging, singular value decomposition and keyhole imaging). Finally, the last part of the manuscript reports the current status of thermosensitive sequences and their dependence on spinlattice relaxation time (T1), were diffusion coefficient (D) and proton chemical shift (delta).

Animals↗
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

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↗
PubMed1998

Metastases to the pancreas.

Disparity in prognosis and management between primary and secondary pancreatic tumours makes recognition of metastases to the pancreas on CT and MRI an important goal. Three different patterns of secondary pancreatic tumours may be seen: localized, multifocal, or diffuse enlargement. CT findings include hypodense lesions, which show rim enhancement following intravenous contrast medium. On MR examination, the lesions are usually hypointense on T1 weighted and hyperintense on T2 weighted images.

Female↗
PubMed1998

[MRCP (magnetic resonance cholangiopancreatography)--an assessment of current status].

For the first time, magnetic resonance cholangiopancretography (MRCP) provides images of the biliary and pancreatic ducts based on 3D data similar to those we are used to from endoscopic retrograde cholangiopancreatography (ERCP) and percutaneous transhepatic cholangiography (PTC). Extraordinarily impressing is the fact that no contrast media have to be applied. The following manuscript shows technical basics and the development of this technique from gradient echo sequences to the recent single-shot techniques. Furthermore possibilities and limitations of MRCP will be discussed with respect to certain illnesses.

Bile Duct Neoplasms↗
PubMed1998

[Diagnosis of gallstone ileus].

Gallstone ileus is a rare disorder, which, because it is often misdiagnosed preoperatively, may become life-threatening. The classic triad of Rigler (aerobilia, small bowel ileus and a calcified, dystopic stone) is visualized on abdominal plain films in only 14-35% of cases. Further work-up includes ultrasound, upper gastrointestinal series with water soluble contrast medium and computed tomography (CT). CT is especially reliable in demonstrating all three criteria.

Aged↗
PubMed1997

[Radiation exposure in digital micturition cystourethrography in children. How much exposure by fluoroscopy?].

OBJECTIVE: Determination of the proportion of the dose-area product caused by fluoroscopy at voiding cystourethrography in children, using digital image intensifier technology. PATIENTS AND METHODS: Using computer-assisted dosimetry, we determined the dose-area product and the respective proportions of the dose-area product caused by fluoroscopy and radiography as well as the number of radiographs taken at a given examination of 40 children (8 children less than 2 years old, 15 children between 2 and 6 years old and 17 children between 6 and 15 years old). RESULTS: The computer software program correctly differentiated between fluoroscopy and radiography in 80% of cases. Incorrect results were primarily observed in newborns and young children. The total radiation dose ranged in relation to patient age from 22 to 651 cGy x cm2. Fluoroscopy was responsible for an average 78% of the applied radiation dose. CONCLUSION: Computer-assisted dosimetry is useful in determining the proportion of the dose-area product caused by fluoroscopy in older children undergoing voiding cystourethrography. When image intensifier technology is used, this accounts for more than 75% of the total radiation dose. The method is not suitable for use in small children.

Adolescent↗
PubMed1997

Bone and soft tissue manifestations of alveolar echinococcosis.

OBJECTIVE: The present study demonstrates the osseous and soft tissue manifestations of alveolar echinococcosis (AE). PATIENTS: We report on eight patients with AE with bone or soft tissue involvement confirmed at biopsy or needle cytology. RESULTS: All eight patients showed hepatic involvement. Four exhibited infiltration of the spine as a result of direct spread of the hepatic primary lesion; distant metastases were observed in only three of these patients. Calcifications, which are typical for hepatic manifestations of the disease, were observed in soft tissue in only two of eight cases (25%); we observed no instances of endovesicular daughter cysts. CONCLUSIONS: AE manifests itself in the vertebral column as a form of spondylitis and in soft tissue presents similar to an abscess. Since in most of these cases spread of the disease per continuitatem from the liver is present, the diagnosis is easily made from the characteristic hepatic findings.

Adult↗
PubMed1997

[MR enteroclysis for nuclear spin tomographic diagnosis of inflammatory bowel diseases with contrast enhancement].

PURPOSE: To evaluate MRI for effectiveness in assessment of intra- and extramural changes in the small intestine. METHODS: 40 patients with known or suspected small bowel disease underwent MR imaging immediately after conventional enteroclysis with barium and a mixture of methyl cellulose and gadolinium-DTPA. RESULTS: In 6 of 24 patients with no pathological findings in conventional enteroclysis, intraabdominal pathology such as thickening of the intestinal wall and an abscess were identified. In the remaining patients, MRI showed good correlation with conventionally obtained data and provided important additional information regarding extraluminal involvement such as enlargement of mesenterial lymph nodes and fistulas as well as abscesses. CONCLUSIONS: MRI, carried out using this technique, provides important additional information regarding intra- and extraluminal changes with good image quality.

Adolescent↗
PubMed1997

Musculoskeletal involvement in cystic echinococcosis: report of eight cases and review of the literature.

OBJECTIVE: Our purpose was to describe the morphologic appearance of musculoskeletal lesions in patients with cystic echinococcosis shown by CT and MR imaging. CONCLUSION: Patients with musculoskeletal lesions of cystic echinococcosis typically have cystic structures in adjacent soft tissues. These cysts morphologically resemble abscesses, with peripheral uptake of contrast medium and variable signal intensities on T1-weighted MR images. The absence of calcifications or endovesicular daughter cysts does not exclude the diagnosis of cystic echinococcosis.

Adult↗
PubMed1997

Comparison of real-time virtual and fiberoptic bronchoscopy in patients with bronchial carcinoma: opportunities and limitations.

OBJECTIVE: Both helical CT and fiberoptic bronchoscopy are used in the staging of pulmonary tumors for therapeutic decision making. The improved resolution offered by helical CT has led to the clinical use of three-dimensional reconstruction techniques such as virtual bronchoscopy. We tested this new simulated endoscopic view of inner organ surfaces and compared it with corresponding fiberoptic examinations of the tracheobronchial system. SUBJECTS AND METHODS: Twenty patients with malignancies of the lung and mediastinum were examined with both virtual bronchoscopy and fiberoptic bronchoscopy. Both examinations were reviewed by radiologists and surgeons familiar with fiberoptic bronchoscopy. Virtual bronchoscopy was calculated and reconstructed from the cross-sectional images on a separate workstation. Stenoses and tumor infiltration were classified from the fiberoptic examination. These results were compared with the virtual bronchoscopy findings. RESULTS: Virtual bronchoscopy of diagnostic quality was achieved in 19 of 20 patients. High-grade stenoses were revealed equally well with virtual and fiberoptic techniques. Virtual bronchoscopy offered the advantage of being able to visualize areas beyond even high-grade stenoses. However, on virtual bronchoscopy discrete infiltration or extraluminal impression was not visible in five patients. In another patient, strong heart pulsation produced motion artifacts that prevented evaluation of the reconstruction. CONCLUSION: Virtual bronchoscopy represents a new noninvasive method for evaluating helical CT findings. In comparison with fiberoptic bronchoscopy, virtual bronchoscopy offers the advantage of being able to visualize areas beyond even high-grade stenoses. In addition to the limited view of fiberoptic bronchoscopy, extraluminal causes of lumen compressions can be analyzed in the cross-sectional images and evaluated together with the virtual representation. However, it was not possible to detect small infiltrations with virtual bronchoscopy. This new representation of helical CT data might be helpful for postoperative follow-up examinations, such as after stent implantation, and can be carried out without additional risk to the patient. Radiologists do need special fiberoptic bronchoscopy knowledge and experience with three-dimensional-reconstructions to differentiate between real stenoses and artificial stenoses that might be caused by pulsation artifacts.

Artifacts↗
PubMed1996

[The diuresis urogram in patients with a bladder replacement].

PURPOSE: To differentiate between urodynamically relevant obstruction and functionally unimportant dilation of the upper urinary tract in patients with neobladder using a modified furosemide urogram. METHOD: An excretory urogram with furosemide loading was carried out in 19 patients with neobladder and sonographically and urographically confirmed dilation of the upper urinary tract. Once strong contrasting of the renal pelves and calyces has been achieved, 20 mg of furosemide were applied and late radiographs were obtained at 15 min and 30 min, respectively. An obstruction was defined as increasing dilation of the renal pelves and calices during forced diuresis and lack of washout effect of the contrast medium. RESULTS: In 32 cases, the renoureteral unit (RUU) was dilated on ultrasound. Of these, 25 RUU's showed good emptiness of contrast medium upon stimulation of diuresis, six RUU's returned a borderline findings, while one RUU was found to exhibit a decompensated anastomotic stenosis, which was dilated. Two further patients with borderline findings were later treated surgically due to their pain symptoms. No patient required further preoperative diagnostic procedures. CONCLUSIONS: The modified furosemide urogram represents a cost-effective diagnostic orientation strategy in patients with neobladder and dilated renal pelves and calyces and is both well-tolerated by patients and meets with broad acceptance from the urologic staff.

Adult↗
PubMed1996

[Virtual cystoscopy based on spiral CT data].

Simulation of three-dimensional cystoscopy based on helical CT scan data in real-time in patients with tumours of the urinary bladder. In three patients with histologically confirmed carcinoma of the urinary bladder, a helical CT scan with double detector technology was carried out preoperatively. A native scan was first performed, followed by an examination in the early contrast medium enhanced phase. After adequate contrasting of the urinary bladder (30 minutes latency), further images were acquired. These data were transferred to a separate graphic computer workstation and reconstructed. The results were then compared with the cystoscopic and pathohistological findings. All tumours of the urinary bladder identified at fiberoptic cystoscopy were also visualised by virtual cystoscopy. The best reconstruction results were obtained from data acquired after the 30-minute latency period. Virtual cystoscopy represents an interesting option in helical CT scanning, which is able to visualise polypoid tumours of the urinary bladder. Its clinical relevance, however, must be demonstrated in studies with a larger number of patients examined.

Aged↗