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S Wildermuth

Publications and source records attributed to S Wildermuth.

48 records · Page 3Linked to original sources
PubMed1995

Real-time biplanar needle tracking for interventional MR imaging procedures.

PURPOSE: To evaluate real-time biplanar tracking of a specially designed needle with magnetic resonance (MR) imaging guidance. MATERIALS AND METHODS: The needle is made of polyetheretherketone and has a miniature radio-frequency coil incorporated into the tip. Tracking software on two workstations is used to compute three-dimensional coordinates of the coil and to display the position as a moving symbol in two imaging planes. Validation of needle tracking was performed in a harvested human liver. T2-weighted fast spin-echo images were used to target a 1-cm cyst. Success of needle placement was confirmed with aspiration and with updated gradient-recalled-echo images. RESULTS: The cyst was successfully targeted from different approaches. Tracking procedures were monitored in real time simultaneously on two separate images. CONCLUSION: Real-time biplanar needle tracking may prove to be useful for both diagnostic and therapeutic interventional MR imaging procedures.

Artifacts↗
PubMed1995

Intravascular MR tracking catheter: preliminary experimental evaluation.

OBJECTIVE: This article reports on the preliminary evaluation of a new technique for guiding intravascular interventional procedures with MR imaging. Active real-time position monitoring of catheters with MR imaging is made possible by incorporating a small RF coil into the tip of the catheter. The purpose of this study was to evaluate the practicability and localizing precision of this MR catheter tracking technique in vitro and in vivo in comparison with fluoroscopy. MATERIALS AND METHODS: Feed cables employing a 0.9-mm-diameter coaxial cable, a 0.5-mm-diameter partially shielded coaxial cable, and a twisted pair cable attaching RF coils at the catheter tip to a coaxial plug at the catheter base were assessed. Further, miniature copper loop RF coils of two, three, and four turns were tested. In vitro validation of MR tracking was achieved by using a phantom consisting of a water-filled harvested segment of human aorta and iliac arteries embedded in gel. Accuracy of catheter placement was compared with MR and fluoroscopy. Subsequently, the MR tracking technique was evaluated in a swine model using a prototype 5-French MR tracking catheter. RESULTS: A fully shielded coaxial cable was found to be crucial for localizing the attached RF coil by means of the tracking technique. The number of coil turns had a lesser impact. Positions of the catheter tip measured with the MR technique and with fluoroscopy correlated well (r > .98), with a 6-mm 95% confidence interval of positional differences. Active real-time tracking of the coil-tipped catheters was achieved both in vitro and in vivo. The 5-French tracking catheter was successfully placed in the splenic and renal arteries of the swine. CONCLUSION: Robust in vivo tracking and accurate placement of catheters equipped with miniature RF coils are possible with MR imaging.

Animals↗
PubMed1994

Cardiac volumetry. Comparison of echoplanar and conventional cine-magnetic resonance data-acquisition strategies.

RATIONALE AND OBJECTIVES: Ejection fraction (EF) measurements obtained using conventional cine-magnetic resonance imaging (MRI) are accurate but time-consuming. With echoplanar imaging (EPI), these data can be acquired much faster. In this study, EF and cardiac output (CO) measurements based on EPI data are compared with those measurements based on cine-MRI images. METHODS: Twelve subjects were examined on a 1.5-T imager equipped with a special EPI gradient system. The entire heart was imaged with contiguous axial 10-mm sections using cine-MRI and EPI techniques. With cine-MRI, 20 frames were acquired over 256 cardiac cycles; with EPI, 24 frames were obtained over four RR intervals using an electrocardiogram-triggered four-shot acquisition strategy. Ejection fraction and CO were calculated based on the summation of the individual end-systolic and end-diastolic volumes. Ejection fraction and CO measurements based on the two different data sets were compared. RESULTS: Multishot EPI was 50 times faster than cine-MRI. The short acquisition time permitted breath-hold imaging. The high temporal (16 to 24 frames/RR interval) and spatial resolution (1.56 x 1.56 mm in plane) of the multishot EPI images enabled delineation of the ventricular lumen at end-systole and end-diastole in a fashion similar to cine-MRI. Echoplanar imaging EF and CO measurements correlated well with cine-MRI EF measurements, with correlation coefficients of 0.96 and 0.94, respectively. The 95% confidence interval of the EF measurement differences between the two techniques was narrow, ranging from -5.2 to 5.7 EF percentage points. CONCLUSIONS: Accurate volumetric EF and CO measurements are possible based on ultrafast multishot EPI data sets as part of an integrated MRI-based cardiac evaluation.

Adult↗
PubMed1993

Scintillation proximity assay for calcitriol in serum without high pressure liquid chromatography.

A rapid isolation step for 1,25-dihydroxyvitamin D3 without high pressure liquid chromatography (HPLC) and a sensitive radioimmunoassay (RIA) have been developed. The time required for extraction and isolation with a combination of Extrelut-1-minicolumns and Sep-Pak silica cartridges from as little as 0.5 ml serum is only 2 h. The assay can be counted after 8 h of incubation. It is performed in the vial that collects the eluate, thus eliminating transfer losses and errors. No separation of bound and free hormone is necessary before beta-counting in the scintillation proximity assay. The detection limit of the assay is 2.7 ng/l. The intra-assay coefficients of variation are 7.3% and 5.2% for samples with calcitriol concentrations of 31 and 148 ng/l, respectively. The inter-assay coefficients of variation are 11.3%, 13.3% and 16.1% for low (16 ng/l), medium (30 ng/l) and high (148 ng/l) control pool samples, respectively. Normal values for calcitriol range from 32 to 80 ng/l. Elderly subjects, patients with reduced kidney function and pregnant women were also evaluated for their calcitriol levels. This assay correlates well with a RIA employing HPLC prepurification and charcoal separation of bound/free calcitriol (r = 0.94).

Adult↗
PubMedDate not supplied

Flow quantitation with echo-planar phase-contrast velocity mapping: in vitro and in vivo evaluation.

We present a multishot echo-planar imaging (EPI) phase-contrast implementation for flow quantitation. The measurement accuracy of this technique was evaluated in vitro and in vivo. A gated eight-shot EPI phase-contrast sequence (TR/TE = 16/7.4, 45 degrees flip angle), with a flow-phase interval of 32 msec and an in-plane resolution of 2 x 2 mm was initially evaluated in a pulsatile flow phantom. Subsequently, EPI phase-contrast flow measurements of the ascending and descending aorta, obtained in 10 volunteers, were compared with flow volume data acquired with a conventional cine phase-contrast sequence (TR/TE = 24/7, 45 degrees flip angle, 48-msec flow-phase interval, 2 x 1 mm in-plane resolution). Comparisons between flow measurements were made using data obtained with the flow probe and cine phase contrast as the standard of reference for in vitro and in vivo measurements, respectively. EPI phase-contrast sequences reduced data acquisition times tenfold compared with cine phase-contrast sequences. EPI phase-contrast flow measurements correlated well with phantom flow (r = .98, slope = 1.1) as well as with aortic cine phase-contrast flow volume determinations (r = .98). A 95% confidence interval of measurement differences between echo-planar and cine phase-contrast imaging, ranging from 2.0 to -1058 mL/min was computed. Ultrafast phase-contrast flow measurements are possible. Multishot EPI phase-contrast imaging provides high measurement accuracy in pulsatile vessels while keeping the image acquisition interval short enough to be accomplished in a comfortable breath-hold.

Adult↗
PubMedDate not supplied

Cardiac imaging: comparison of two-shot echo-planar imaging with fast segmented K-space and conventional gradient-echo cine acquisitions.

We compared the cardiac image quality of multishot echo-planar imaging (EPI), segmented K-space, and conventional cine acquisitions. Three techniques were used to obtain gated multiphase acquisitions of an axial section traversing both ventricles in 10 volunteers: two-shot EPI acquired nonsequentially over two heart beats breath-held; segmented K-space cine with eight K-space lines acquired per cardiac trigger over 16 R-R intervals, also breath-held; and 24 cine phases obtained over 256 R-R intervals. Intraventricular SNRs with two-shot EPI were superior to segmented K-space cine acquisitions (P < .005) and not statistically different from conventional cine acquisitions (P < .1). Intraventricular signal was most homogeneous on conventional cine images (P < .05). Coronary artery visualization and myocardial delineation were better on the EPI image set than on segmented K-space cine images (P < .05). Two-shot EPI provides high-quality gated cardiac images with an acquisition time of only 2 seconds.

Adult↗
PubMedDate not supplied

Advances in vascular echoplanar imaging.

Magnetic resonance (MR) angiography is emerging as an increasingly useful tool for the noninvasive evaluation of the cardiovascular system. Ultrafast echoplanar imaging (EPI) data acquisition strategies are becoming more widely available. When applied to MR angiography, the associated reduction in data collection time allows breathheld acquisitions of entire vascular territories, as well as the exploitation of short-lived flow-enhancing measures. This paper describes technical aspects of EPI, its implementation into vascular imaging sequences, and associated artifacts. This is followed by a discussion of potential EPI MRA applications in the carotid and renal arteries, the portal venous system, and arteries and veins of the lower leg.

Arteries↗
PubMedDate not supplied

Juvenile granulosa cell tumor.

We present three-dimensional computed tomographic findings of a juvenile granulosa cell tumor of the ovary at FIGO stage IA in a 17-year-old woman. Juvenile granulosa cell tumor is one of the rare sex cord stromal tumors of the ovary. Most tumors at FIGO stage IA have a favorable prognosis, whereas those at higher stages have a less favorable outcome.

Adolescent↗
PubMedDate not supplied

MR-guided percutaneous angioplasty: assessment of tracking safety, catheter handling and functionality.

PURPOSE: Magnetic resonance (MR)-guided percutaneous vascular interventions have evolved to a practical possibility with the advent of open-configuration MR systems and real-time tracking techniques. The purpose of this study was to assess an MR-tracking percutaneous transluminal angioplasty (PTA) catheter with regard to its safety profile and functionality. METHODS: Real-time, biplanar tracking of the PTA catheter was made possible by incorporating a small radiofrequency (RF) coil in the catheter tip and connecting it to a coaxial cable embedded in the catheter wall. To evaluate potentially hazardous thermal effects due to the incorporation of the coil, temperature measurements were performed within and around the coil under various scanning and tracking conditions at 1.5 Tesla (T). Catheter force transmission and balloon-burst pressure of the MR-tracking PTA catheter were compared with those of a standard PTA catheter. The dilatative capability of the angioplasty balloon was assessed in vitro as well as in vivo, in an isolated femoral artery segment in a swine. RESULTS: The degree of heating at the RF coil was directly proportional to the power of the RF pulses. Heating was negligible with MR tracking, conventional spin-echo and low-flip gradient-echo sequences. Sequences with higher duty cycles, such as fast spin echo, produced harmful heating effects. Force transmission of the MR-tracking PTA catheter was slightly inferior to that of the standard PTA catheter, while balloon-burst pressures were similar to those of conventional catheters. The MR-tracking PTA catheter functioned well both in vitro and in vivo. CONCLUSION: The in vivo use of an MR-tracking PTA catheter is safe under most scanning conditions.

Angioplasty, Balloon↗
PubMedDate not supplied

3D phase contrast EPI MR angiography of the carotid arteries.

OBJECTIVE: Our goal was to compare 3D phase contrast (PC) echo planar imaging (EPI) MRA of the carotid and vertebral arteries with conventional 3D PC in volunteers and patients. MATERIALS AND METHODS: The carotid arteries of 12 volunteers were imaged with conventional and EPI 3D PC sequences. The visibility for each of seven carotid and four vertebral segments was qualitatively assessed. Signal intensity and homogeneity determinations were performed on the source images. Three patients with known carotid artery disease were also imaged with the same protocol. RESULTS: EPI reduced 3D PC data acquisition time from 459 to 32 s (factor of 15). Both techniques permitted full assessment of the common carotid artery, the bifurcation, as well as the proximal internal carotid artery (ICA), external carotid artery (ECA), and vertebral arteries. Visualization of the distal ICA/ECA and vertebral arteries was inferior with EPI compared with the conventional acquisition. In all patients, lesions as established by X-ray angiography were seen to equal advantage with both techniques. CONCLUSION: EPI 3D PC MRA renders diagnostic images of the proximal carotid system. The considerable reduction in data acquisition time must be weighed against poorer image quality.

Adult↗
PubMedDate not supplied

Postprocessing techniques for gadolinium-enhanced three-dimensional MR angiography.

Contrast material-enhanced three-dimensional (3D) magnetic resonance (MR) angiography is rapidly gaining acceptance as a versatile noninvasive alternative to conventional angiography. The technique has proved useful in the visualization and assessment of complex pathologic entities in the thoracic and abdominal aorta, renal arteries, pelvic arterial system, and pulmonary arteries. Several postprocessing techniques are available for reformation of the imaging data, including maximum intensity projection (MIP), surface rendering, and virtual intraluminal endoscopy (VIE). MIP and subvolume MIP reconstructions can be produced quickly and are useful for demonstration and archiving purposes. Because of its unique ability to display vessels without overlap, surface rendering is especially useful in depicting diseases that influence either the outer shape of the vessels or their topographic arrangement. VIE allows assessment of the inside of the vascular wall and is helpful in detecting wall-bound thrombus and evaluating the degree of stenosis. Most clinically relevant questions (eg, presence of pulmonary embolism, aortic aneurysm, renal artery stenosis) can be fully answered if analysis is based on MIP and thin multiplanar reformations of contrast-enhanced 3D MR angiograms. In some cases, the use of additional postprocessing techniques enhances diagnostic confidence.

Aorta↗