Biomedical subjects

S Wildermuth

Publications and source records attributed to S Wildermuth.

17 recordsLinked to original sources

PubMed1998

[Vascular applications of interventional MRI].

The flow sensitivity inherent to the MR experiment allows for the non-invasive assessment of both the arterial and venous vasculature in any desired plane with good spatial resolution. Data can be acquired in a three-dimensional form, permitting reformating in any plane. In addition, MRI is capable of providing quantitative blood flow information with the use of phase-contrast flow-mapping techniques. Ultrafast gradient echo and echoplanar data acquisition strategies even permit imaging in near-real time. The availability of open MRI configurations now permits one to take advantage of the unique imaging features inherent to MR imaging for the purpose of guidance and control of various intravascular procedures. With the recent development of the MR tracking and MR profiling techniques, permitting visualization of guide-wires and catheters relative to their surroundings in the MR environment in real time, one of the last obstacles to 'Interventional MR angiography' has in effect been overcome. In addition, MR catheters can be modified to acquire high-resolution MR images of the vascular wall, thereby opening vast possibilities regarding characterization of atherosclerotic plaques. This review introduces the underlying techniques for catheter and guide-wire visualization in the MR environment, describes preliminary interventions in animals and humans and discusses the potential of intravascular MRI.

Echo-Planar Imaging↗

PubMed1998

Lumbar spine: quantitative and qualitative assessment of positional (upright flexion and extension) MR imaging and myelography.

PURPOSE: To compare measurements of the sagittal diameter of the lumbar dural sac obtained at positional magnetic resonance (MR) imaging and at functional myelography and to assess the influence of various body positions on the dural sac and the intervertebral foramina. MATERIALS AND METHODS: Thirty consecutive patients referred for lumbar myelography were examined with an open 0.5-T MR imager, Sagittal T2-weighted fast spin-echo images were acquired with patients in the supine, upright flexion, and upright extension positions. The midsagittal diameter of the dural sac was measured at the level of the disks on MR images and myelograms. Foraminal sizes on the MR images were scored independently by two observers. RESULTS: Correlation between MR imaging and myelographic measurements was high (r = .81-.97). A small but statistically significant positional dependence of the dural sac diameter was found in the lower lumbar spine. Position-dependent differences in foraminal scores were uncommon. CONCLUSION: Quantitative assessment of sagittal dural sac diameters is comparable between lumbar myelography and positional MR imaging. In a selected patient population, only small changes in the sagittal diameter of the dural sac and foraminal size can be expected between various body positions, and the information gained in addition to that from standard MR imaging is limited [corrected].

Adult↗

PubMed1998

Role of CT angiography in patient selection for thrombolytic therapy in acute hemispheric stroke.

BACKGROUND AND PURPOSE: It has been shown that thrombolytic therapy can improve clinical outcome in a subgroup of patients with acute cerebral ischemia. This subgroup was characterized by certain clinical and imaging findings (eg, moderate to severe neurological deficit for less than 3 to 6 hours, occlusion of the middle cerebral artery, lack of extended infarct signs on CT, and efficient leptomeningeal collaterals). Although not part of published prospective randomized rtPA trials, information about the status of the brain vessels would be helpful in the selection of patients who may benefit the most. Our purpose was to determine the feasibility of CT angiography (CTA) in patients with acute hemispheric ischemia and to evaluate its relevance for thrombolytic therapy. METHODS: CTA was performed in 40 consecutive patients (11 women and 29 men; age range, 19 to 80 years) with moderate or severe symptoms (National Institutes of Health Stroke Scale score of > or =8) of acute hemispheric ischemia. CTA findings were compared with Doppler ultrasonography (US; n=22) and intra-arterial digital subtraction angiography (DSA; n=7). Twenty patients received thrombolytic therapy, the remaining patients received intravenous heparin. RESULTS: Images and 3-dimensional reconstructions of diagnostic quality could be obtained in all patients. Thirty-four patients had a vessel occlusion. The extent of leptomeningeal collaterals correlated significantly with the outcome after thrombolytic therapy (rs=0.46, P<0.05). The evaluation of diagnostic accuracy showed a high agreement with US (22 of 22) and DSA (6 of 7). CONCLUSIONS: CTA can provide important information for the initiation of therapy in patients with acute hemispheric ischemia. Identification of patients with autolyzed thrombi, occlusion of the internal carotid artery bifurcation, and poor leptomeningeal collaterals is feasible with the use of CTA. These patients may have little potential for benefit from thrombolytic therapy.

Acute Disease↗

PubMed1997

MR imaging-guided intravascular procedures: initial demonstration in a pig model.

With use of an open 1.5-T magnetic resonance (MR) imager and a tracking catheter, the authors successfully placed the catheter into the left or right sacral artery in pigs. The tracking catheter comprised a 5.3-F percutaneous transluminal angioplasty catheter with a small copper radio-frequency coil in its tip. With use of the coil as an antenna, the catheter tip position was projected in real time onto MR angiography road maps in two planes. Guidance of placement of the catheter with the MR angiography road maps allowed successful embolization, balloon occlusion, and transjugular intrahepatic puncture of the portal system. Specialized catheters can be tracked in vivo to allow MR guidance in intravascular interventional procedures.

Animals↗

PubMed1996

Köbberling-Dunnigan syndrome: a rare cause of generalized muscular hypertrophy.

A 36-year-old woman presented with muscle hypertrophy (particularly of the calves) since puberty, occasional muscle cramps, a musculine habitus, and a loss of subcutaneous fat on limbs and trunk sparing her face, neck, and vulva. Multiple lipomas were found on her trunk, and acanthosis nigricans on her neck. Laboratory testing revealed hyperlipidemia and pathological glucose tolerance with hyperinsulinemia. Physical and laboratory findings are consistent with Köbberling-Dunnigan syndrome, a rare inherited form of lipoatrophy. The patient's mother had the same body habitus and insulin-dependent diabetes mellitus. These cases suggest that partial lipodystrophy also affects muscle and is a cause of genuine muscular hypertrophy.

Adult↗

PubMed1996

Towards active guidewire visualization in interventional magnetic resonance imaging.

Improving the visibility of interventional devices is of paramount importance if MRI-guided fluoroscopy is to become a reality. Passive visualization is problematic in that the susceptibility-induced artifacts are material- and orientation-dependent. Here a concept is presented for making interventional devices visible. It involves fitting a device with a straight-wire antenna. As the sensitivity of such an antenna is highest for signal sources in the immediate neighborhood, using the antenna for reception gives an outline image. In this manner a guidewire or other interventional device could be made MRI-visible. The image appearance of a straight-wire antenna depends on the orientation of the device with respect to the main magnetic field and imaging plane. This phenomena is discussed theoretically and documented with MR images.

Catheterization↗

PubMed1996

Human aorta: preliminary results with virtual endoscopy based on three-dimensional MR imaging data sets.

PURPOSE: To determine the feasibility of use of magnetic resonance (MR) imaging data sets to perform virtual intraarterial endoscopy (VIE). MATERIALS AND METHODS: Seven female and 14 male patients (aged 9-86 years [mean, 42 years]) with various pathologic aortic conditions underwent three-dimensional gadolinium-enhanced spoiled gradient-echo MR imaging. With prototype software, VIE postprocessing algorithms (based on ray casting) were applied to the imaging data sets. Findings at conventional angiography were used as the standards of reference. RESULTS: The vessel wall was seen from the inside in each case, and the following pathologic conditions were depicted clearly: the two lumina in a congenial double aortic arch and the single lumen after correction, vessel narrowing in coarctations, characteristics of Leriche syndrome, stenoses, occlusions, and the true and false lumina of dissections. CONCLUSIONS: Limitations of VIE include the image quality of the original data set, the threshold chosen to minimize intraluminal artifacts, and the inherent smoothing of vessel walls.

Adult↗

PubMed1996

MR venography of the calf: value of flow-enhanced time-of-flight echoplanar imaging.

OBJECTIVE: Release of a tourniquet on the thigh and termination of Valsalva's maneuver result in a transient increase in venous blood flow in the leg. The purpose of this study was to determine the value of time-of-flight echoplanar imaging performed with these flow-enhancing methods to image the veins of the calf. SUBJECTS AND METHODS: Flow volumes in the femoral veins in eight volunteers were determined with a two-dimensional phase-contrast MR imaging technique before and immediately, 20, 40, and 60 sec after termination of Valsalva's maneuver and thigh vein occlusion. Subsequently, the calf veins of 11 healthy volunteers were imaged with a two-dimensional four-shot echoplanar MR imaging technique. Forty-one 5-mm-thick sections were obtained over 10 sec immediately after termination of venous occlusion. Visibility of the three venous bundles was analyzed in the proximal, middle, and distal portions of the calf on the basis of a four-point scale. Finally, the calf of a single patient with documented DVT was imaged by the same MR imaging technique. RESULTS: Both Valsalva's maneuver and venous occlusion caused significant increases in venous flow (p < .05) only during the first 20 sec after termination of the maneuver and the occlusion. Venous occlusion had a significantly greater effect than did Valsalva's maneuver (p < .05). Flow augmentation by venous occlusion of the thigh improved calf vein visualization with time-of-flight echoplanar MR imaging (p < .0001). Of the 99 calf vein segments examined, 93 were clearly seen. Thrombi were seen in the patient study. CONCLUSION: Multishot time-of-flight echoplanar imaging can exploit the short-lived effect of mechanical flow-enhancing measures, resulting in good visualization of calf veins. The true diagnostic impact of this technique needs to be evaluated in a patient study.

Adult↗

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

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↗