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H Greess

Publications and source records attributed to H Greess.

25 records · Page 2Linked to original sources
PubMed1999

[Dosage reduction in computed tomography by anatomy-oriented attenuation-based tube-current modulation: the first clinical results].

PURPOSE: To examine the feasibility of reducing exposition in CT examinations by applying a prototype device for tube current modulation with the image quality remaining unchanged. PATIENTS AND METHODS: The prototype device for tube current modulation was integrated into a Somatom Plus 4 CT scanner (Siemens). The method is based on anatomy-oriented modulation of the tube current. The attenuation of the X-ray beam by the patient's body was determined online, the tube current was adapted to changing anatomy after a delay of 180 degrees. In ten patients undergoing radiotherapy, four identical scans of the shoulder region were carried out with and without tube current modulation. For determining dose reduction, mAs product of both scans were compared. The evaluation of noise artifacts, low contrast detectability and overall image quality was performed by four radiologists in a blinded fashion. RESULTS: Patient doses could be reduced by 38% on an average. Scans with tube current modulation were superior to scans without it as to noise (75%), low contrast detectability (51%), artifacts (69%), and overall image quality (71%). CONCLUSIONS: A significant reduction in exposition during CT can be achieved by anatomy-oriented tube current modulation without image degradation.

Artifacts↗
PubMed1999

Contrast enhanced MRA of peripheral arteries with the automatic "floating table".

Magnetic resonance angiography (MRA) is increasingly used as a non-invasive alternative to digital subtraction angiography (DSA). Besides plain time-of-flight (TOF) and phase contrast (PC) MRA a new MRA technique using positive contrast agent has been introduced recently. A fast 3D gradient-echo sequence is applied to reach a significant reduction of measurement time for acquisition of the MRA within the first pass of the contrast agent, thereby avoiding venous overlap. A significant progress was yielded by MR systems allowing manual table movement for examination of the pelvis and the lower limbs in one examination with a single contrast agent bolus. However, in this case it is necessary to have a coworker in the examination room moving the table manually. In this paper we report a prototype system which allows automatic table movement ("floating table"). Using this novel system we examined a patient with an aneurysm of the abdominal aorta and peripheral arterial occlusive disease (PAOD). Diagnostic results of contrast enhanced MRA and DSA were equivalent. In summary, the automatic floating table system introduced in this paper allows comfortable non-invasive examination of pelvic and lower limb arteries. The value of this technique in comparison to DSA has to be determined in future studies.

Arterial Occlusive Diseases↗
PubMedDate not supplied

Clinical value of MRC in the follow-up of liver transplant patients with a choledochojejunostomy.

BACKGROUND: We investigated the clinical value of magnetic resonance cholangiography (MRC) in liver transplant patients receiving choledochojejunostomy (CDJ). METHODS: Twenty-five MRCs were performed in 23 initially asymptomatic patients 19 months (mean) after liver transplantation with biliary reconstruction via CDJ. The images were evaluated by consensus (two investigators) for bile duct strictures and dilatations. As a standard of reference, clinical follow-up (including laboratory analysis) was used in 20 cases and direct cholangiography or surgery in three cases. RESULTS: Fourteen pathologic findings were observed in 11 patients (anastomotic strictures in four, left or right bile duct strictures in three, and peripheral segmental dilatations with or without strictures in seven). Patients with pathologic MRC findings had significantly higher levels of alkaline phosphatase (p < 0.05) and more frequently had histories of cholangitis than did patients with normal MRC. Four of six patients with stenoses of the central bile ducts subsequently developed biliary complications requiring treatment (three confirmed by direct cholangiography). In patients with unremarkable bile ducts or only peripherally located changes on MRC, no bile duct complications or relevant changes in the cholestasis parameters occurred during follow-up (mean = 30 months). CONCLUSION: MRC can noninvasively detect pathologic biliary tract changes in liver transplant patients in the asymptomatic stage and provide information for planning invasive therapeutic procedures.

Adult↗
PubMedDate not supplied

Virtual labyrinthoscopy: visualization of the inner ear with interactive direct volume rendering.

Computed tomography (CT) is the modality of choice for detailed imaging of the bony labyrinth. Usually, information about the complex three-dimensional anatomic structures of the inner ear is presented as two-dimensional section images. Interactive direct volume rendering is a powerful method for visualization of the labyrinth. Unlike other visualization methods, direct volume rendering enables direct visualization of the bony labyrinth without explicit segmentation prior to the visualization process. Direct volume rendering was applied to visualization of the structures of the temporal bone in five patients without pathologic conditions and four patients with pathologic conditions. In all cases, clear representations of the bony labyrinth and the facial canal were provided. Because standard CT examinations combined with interactive visualization based on direct volume rendering are used, the method is fast and flexible. Therefore, this approach is applicable in routine clinical work. Problems occur in patients with effusion in the temporal bone because adjustment of imaging parameters for proper delineation of the target structures is difficult in this situation. However, direct volume rendering can produce meaningful images of high quality even in these problematic cases. The term virtual labyrinthoscopy is suggested for visualization of the labyrinth by using direct volume rendering.

Cochlea↗