Biomedical subjects

S Duewell

Publications and source records attributed to S Duewell.

At least 19 recordsLinked to original sources

PubMed2000

Hepatic fascioliasis: report of two cases.

Two cases of hepatic fascioliasis with characteristic features in US examinations and CT scans are presented. In both modalities they show tunnel-like branching and clustered areas of low echogenicity/density, which reach subcapsular regions. These cases are presented to recall the imaging features in hepatic fascioliasis especially outside endemic regions. Not only CT but also US is able to detect these characteristic lesions, which may help to make the diagnosis of hepatic fascioliasis in patients with clinical symptoms suggestive of parasitic disease.

Acute Disease↗

PubMed1999

Changes in cross-sectional measurements of the spinal canal and intervertebral foramina as a function of body position: in vivo studies on an open-configuration MR system.

OBJECTIVE: The purpose of this study was to evaluate physiologic changes of the cross-sectional area of the spinal canal and neural foramina in young asymptomatic volunteers. SUBJECTS AND METHODS: Twelve asymptomatic volunteers were examined in a 0.5-T open-configuration MR system. T2-weighted fast spin-echo sequences were obtained in upright neutral, upright flexed, upright extended, and supine extended positions. The cross-sectional area of the spinal canal and the thickness of the ligamentum flavum were measured on angled axial images at the L4-L5 level. The anteroposterior diameter of the spinal canal and cross-sectional areas of the neural foramina were measured on sagittal images from L1 to S1. RESULTS: At disk level, the cross-sectional area of the spinal canal varied significantly between body positions, most notably between the upright flexed (mean, 268 mm2) and the upright extended (mean, 224 mm2) positions (p < .0001). The maximum thickness of the ligamenta flava increased in the extended positions (p < .0001). The cross-sectional area of the neural foramina underwent position-dependent variations of as much as 44.4%. The smallest cross-sectional areas were found in the extended positions. CONCLUSION: In asymptomatic volunteers, MR imaging is able to show position-dependent changes in the cross-sectional areas of the spinal canal and the intervertebral foramina. The extended positions best reveal important findings.

Adult↗

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

Differentiation of necrotizing fasciitis and cellulitis using MR imaging.

OBJECTIVE: This study was performed to evaluate the diagnostic value of MR imaging in differentiating necrotizing fasciitis from cellulitis. MATERIALS AND METHODS: Spin-echo T1-weighted, T2-weighted, and contrast-enhanced T1-weighted spin-echo sequences were performed in 15 patients with clinically suspected necrotizing fasciitis. In two other patients, only unenhanced imaging was performed. The MR imaging results were correlated with the surgical findings in 11 cases, with autopsy in one case, and with the clinical outcome in five cases. RESULTS: Cellulitis was diagnosed when subcutaneous thickening with fluid collections was revealed on T2-weighted images and when subcutaneous tissue or superficial fascia or both showed contrast enhancement. For the diagnosis of necrotizing fasciitis, imaging revealed additional involvement of deep fasciae with fluid collections, thickening, and enhancement after contrast administration. According to these criteria, we found 11 cases of necrotizing fasciitis and six of cellulitis. MR imaging identified all 11 cases of necrotizing fasciitis correctly when compared with the surgical findings. One false-positive case of cellulitis was overstaged and was thought to be necrotizing fasciitis. Contrast-enhanced T1-weighted sequences delineated abscesses and areas of necrosis more clearly than T2-weighted sequences did, but showed no additional lesions. CONCLUSION: When no deep fascial involvement is revealed with MR imaging, necrotizing fasciitis can be excluded. However, because its sensitivity exceeds its specificity, MR imaging tends to overestimate the extent of deep fascial involvement. Therefore, the therapeutic regimen should be based on a combination of clinical findings and MR imaging.

Adult↗

PubMed1996

Evaluation of methemoglobin as an autologous intravascular MRI contrast agent.

Methemoglobin (MetHb) was evaluated as an intravascular paramagnetic contrast agent. Methemoglobin formation was induced by 4-dimethylaminophenol (4-DMAP), causing a reduction in blood T2* in vitro. The 4-DMAP generated metHb with a time constant of 62 s. A 4-DMAP bolus did not decrease measurably the signal intensity in the in vivo rabbit kidney in the first pass. At steady state, a MetHb concentration of 24.8 +/- 2.3% resulted in a signal decrease of 9.2 +/- 2.6% in the kidney. Methemoglobin is an effective vascular T2* relaxation agent, but the formation of MetHb by 4-DMAP is too slow for first-pass imaging. A more effective conversion agent resulting in a bolus of at least 25% MetHb within 5 s would result in a detectable first-pass signal and a viable contrast technique.

4-Aminopyridine↗

PubMed1996

The evaluation of dielectric resonators containing H2O or D2O as RF coils for high-field MR imaging and spectroscopy.

Electromagnetic resonators consisting of low-loss dielectric material and/or metallic boundaries are widely used in microwave technologies. These dielectric resonators usually have high Q factors and well-defined field distributions. Magnetic resonance imaging was shown as a way of visualizing the magnetic field distribution of the resonant modes of these resonators, if the dielectric body contains NMR sensitive nuclei. Dielectric resonators have also been proposed as RF coils for magnetic resonance experiments. The feasibility of this idea in high-field MR is discussed here. Specifically, the dielectric resonances of cylindrical water columns were characterized at 170.7 MHz (4 T 1H Larmor frequency), and evaluated as NMR transmit and receive coils. The dielectric resonance of a cylindrical volume of D2O was used to image a hand at 170.7 MHz. This study demonstrated that MRI is an effective way of visualizing the magnetic field in dielectric structures such as a water cylinder, and can potentially be generalized to solid-state dielectric devices. The possible applications of dielectric resonators other than simple cylindrical volumes in MRI and MR solution spectroscopy at high field strengths are also discussed.

Deuterium↗

PubMed1996

Improved growth with bioabsorbable sutures in both high- and low-pressure zones.

BACKGROUND: Compromised growth after operation remains a significant problem in the cardiovascular field. Some benefit of absorbable suture materials has been demonstrated for arterial anastomoses. However, for the low-pressure zone, few data are available. METHODS: To assess growth in high- versus low-pressure zones we transected the abdominal aorta (high-pressure zone) as well as the inferior vena cava (low-pressure zone) in 10 young mongrel dogs using for reanastomosis 7-0 nonabsorbable versus absorbable running sutures in random order. RESULTS: All animals survived and were evaluated over 12 months including body weight (gain, 212% +/- 45% for nonabsorbable versus 218% +/- 8% for absorbable; not significant), angiography, and, after elective sacrifice, detailed studies of aorta and vena cava. Systematic complication of angiographic data at 12 months showed at the suture level an area of 13.8 mm2 for nonabsorbable versus 24.3 +/- 14.4 mm2 for absorbable sutures in the high-pressure zone as compared with 12.9 +/- 4.9 mm2 for nonabsorbable versus 25.3 +/- 15.4 mm2 for absorbable sutures in the low-pressure zone. Residual lumen, calculated as a function of the area above and below the suture, accounted for 35% +/- 10% for nonabsorbable versus 92% +/- 12% for absorbable sutures (p < 0.001) in the high-pressure zone as compared with 37% +/- 13% for nonabsorbable versus 75% +/- 15% for absorbable sutures (p < 0.003) in the low-pressure zone (high versus low, not significant). Poststenotic dilatation accounted for 199% +/- 22% for nonabsorbable versus 126% +/- 43% for absorbable sutures (p < 0.01) in the high-pressure zone. In the low-pressure zone, poststenotic dilatation remained below the inflow area, and the residual poststenotic lumen accounted for 52% +/- 14% for nonabsorbable versus 77% +/- 16% for absorbable sutures (p < 0.004). Macroscopic, light, and scanning electron microscopic studies confirmed different growth patterns in high- versus low-pressure zones. CONCLUSIONS: Aortic narrowing resulted in poststenotic dilatation and unrestricted outflow path (hourglass-type stenosis). Caval narrowing was followed by restriction of poststenotic outflow path (funnel-type stenosis). Absorbable suture material allows for superior growth in both high- and low-pressure zones.

Absorption↗

PubMed1996

MR relaxation times in human brain: measurement at 4 T.

PURPOSE: To determine the values for relaxation times in human brain for magnetic resonance (MR) imaging at 4 T. MATERIALS AND METHODS: T1 measurements were made with a progressive saturation sequence, an implementation of the Look-Locker sequence, and an inversion-recovery (IR) interleaved echo-planar imaging (IEPI) sequence. T2 measurements were made with a standard spin-echo (SE) sequence and an SE IEPI sequence. RESULTS: The T1 measurements yielded values of 1,724 msec +/- 51 for gray matter, 1,043 msec +/- 27 for white matter, and 4,550 msec +/- 800 msec for cerebrospinal fluid. The deep gray matter regions had T1 values of 1,458 +/- 38 (caudate nucleus) and 1,372 +/- 60 (putamen). The T2 measurements yielded results of 63 msec +/- 6.2 for gray matter and 49.8 msec +/- 2.2 for white matter. CONCLUSION: The T1 values measured at 4 T show a higher value than predicted from extrapolation at lower field strengths. The T2 measurements showed a slight decrease in values over those measured at lower-field strength. The gain in signal-to-noise ratio from the higher field strength may be substantially offset by these altered relaxation time values to a degree that is sequence dependent.

Adult↗

PubMed1996

MR imaging contrast in human brain tissue: assessment and optimization at 4 T.

PURPOSE: To evaluate multiple magnetic resonance (MR) imaging sequences for their ability to provide T1 and T2-weighted images at a field strength of 4 T, and to validate previously obtained relaxation time measurements. MATERIALS AND METHODS: Different spin-echo, inversion-recovery (IR), gradient-recalled acquisition in the steady state (GRASS), and magnetization transfer contrast-enhanced GRASS sequences were evaluated in a single section, each in at least four volunteers. Also, interleaved echo-planar imaging (IEPI) and interleaved gradient-recalled echo (IGRE) sequences were analyzed and compared with standard sequences. RESULTS: Predicted contrast behavior, according to MR relaxation time measurements, was found to agree well with that of the validation experiments. Fair T1 contrast can be achieved on MR images at 4 T, contrary to early predictions. Under other conditions, however, such as partially spin-density-weighted parameters, lower contrast is observed at the high field strength when compared with conventional field strengths. CONCLUSION: The longer T1 values at higher field strengths have a substantial effect on image contrast. Depending on the sequence and parameters chosen, good image contrast can be realized at 4 T. IEPI and hybrid IR IGRE sequences are useful in shortening the prolonged examination times owing to the longer T1 values at higher field strengths.

Artifacts↗

PubMed1995

[Rare association of a coronary fistula with a fusiform aneurysm of the superior vena cava: diagnosis via transesophageal echocardiography and MRI].

A congenital fistula of the left circumflex coronary artery with large aneurysmal sacculations and drainage into the vena cava superior is reported in an asymptomatic black adult female. An indicator dilution curve excluded a significant left-to-right shunt. In addition, the patient had a large fusiform aneurysm of the superior vena cava with maximal extension in the anterior upper mediastinum. Transesophageal Doppler echocardiography and magnetic resonance imaging were complementary diagnostic tools, the first for clearly visualizing coronary anatomy and shunt, the second for accurate imaging of the aneurysmal vena cava superior in the upper mediastinum.

Adult↗

PubMed1994

Differences in biodistribution of the anti-(carcinoembryonic antigen) murine monoclonal antibody CE-25, its F(ab')2 fragment and its intact mainly human chimeric form CE 4-8-13. Dependence on tumour size and amount of antibody injected.

The effect of the size of the tumour and the amount of antibody injected on the biodistribution of a family of radioiodinated antibodies was studied. The intact mouse anti-(carcinoembryonic antigen) (anti-CEA) monoclonal antibody CE-25, its F(ab')2 fragment and the intact human-mouse chimeric from CE 4-8-13 were evaluated in a model system using the human CEA-producing colon xenograft T 380 grown in nude mice. The relative retention (the percentage of the injected dose per gram of tissue), of mouse mAb and F(ab')2 in tumour and most normal tissues 1 day after injection was independent of the antibody dose; after 4 days the mAb values increased with increasing antibody dose. The relative retention of chimeric mAb increased with increasing antibody dose 1 day after injection and also slightly after 4 days. The relative retention in tumour tissue was lower in bigger xenografts for all antibodies. The relative retention of mouse mAb in small tumours increased from day 1 to day 4; for chimeric mAb this value decreased. In normal tissues the relative retention of mouse mAb decreased from day 1 to day 4, but the relative retention of chimeric mAb in normal tissue dropped rapidly and changed little afterwards. Thus the biokinetics of antibodies is "species"-dependent: foreign, mainly human, chimeric antibody clears faster from normal mouse tissue than mouse antibody and reaches lower concentrations.

Animals↗

PubMed1994

[Fat-suppressed MR imaging sequences in the diagnosis of liver and pancreatic neoplasms at 1.5 tesla].

We investigated 55 patients with suspected neoplasms of the liver and/or pancreas using fat-suppressed spin echo and gradient echo MR sequences. T1 and T2 weighted fat-suppressed spin echo sequences provided higher sensitivity for the detection of liver metastases. In the diagnosis of pancreatic tumours, T1 weighted fat-suppressed gradient echo sequences after application of intravenous and oral paramagnetic contrast agents offered more information than other sequences. Drawbacks of fat-suppressed sequences are an increase in scan time and inhomogeneous fat-suppression at the periphery of the image.

Adipose Tissue↗

PubMed1994

Normal heart: evaluation with echo-planar MR imaging.

PURPOSE: To evaluate the appearance of the heart on spin-echo (SE) and gradient-echo (GRE) echo-planar magnetic resonance (MR) images. MATERIALS AND METHODS: Nine healthy volunteers were examined with an MR imager with transaxial echo-planar imaging (EPI) capabilities. SE EPI and GRE EPI sequences were used. Full k-space signal was obtained with readout time of 40 msec per image, and total image acquisition time was 72 and 52 msec, respectively, for SE EPI and GRE EPI. RESULTS: Delineation of cardiac structures was superior with SE EPI, reflective of significantly higher contrast between myocardial and intraluminal signal intensity (SI) (P < .001). The higher (P < .01) and more homogeneous (P < .001) intraluminal SI with GRE EPI allowed better assessment of intracardiac flow. Septal SI was significantly higher for GRE EPI (P < .01), but signal homogeneity was similar for both sequences (P > .2). CONCLUSION: Diagnostic images of the heart were obtained with both SE EPI and GRE EPI. GRE EPI is more suitable for flow studies because of the higher and more homogeneous intravascular SI.

Adult↗

PubMed1993

The value of bone scintigraphy, bone marrow scintigraphy and fast spin-echo magnetic resonance imaging in staging of patients with malignant solid tumours: a prospective study.

The purpose of this prospective study was to define the value of bone scintigraphy (BS), bone marrow scintigraphy (BMS) and the new fast spin-echo (FSE) magnetic resonance imaging (MRI) sequences in screening for bone metastases in patients with solid malignant tumours. It was our particular interest to classify patients into a group with and a group without bone metastases, and not only to compare the absolute number of metastases detected by each method. Thirty-two patients were examined using technetium-99m dicarboxy propane diphosphonate bone scintigraphy, 99Tc-labelled monoclonal anti-granulocyte antibodies for bone marrow scintigraphy and 1.5 T MRI using T1-weighted and FSE T2-weighted sequences. Against a reference standard obtained by re-evaluation of all clinical and imaging data 1 year after prospective BS, BMS and MRI had been performed, the three imaging modalities were falsely positive in two, eight and two cases and falsely negative in zero and four cases, respectively. BMS was falsely positive in eight patients because of vertebral marrow degeneration which caused photopenic defects which could not be differentiated from metastases. MRI showed these lesions to unequivocally contain fat. BMS and MRI were falsely negative in four cases because of the limited field of examination. In our study the key factor in classifying a patient as bone M1 or M0 was the possibility of surveying the entire skeleton, as is the case in BS, and not that MRI had a higher sensitivity compared to BS when analysis was on a lesion-by-lesion basis.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1993

[Reduction of MRT time in the female pelvis using T2-weighted Fast-Spinecho(FSE)-technique. A quantitative and qualitative comparison of conventional spinecho(SE) and Fast-Spinecho(FSE)-sequence].

The fast spin echo (FSE) technique leads to time saving by individual phase coding of several spin echoes within one repetition interval. The new sequencing was compared quantitatively and qualitatively with conventional spin echo sequences in 30 patients with gynaecological pelvic disease. The signal-to-noise ratio was higher on FSE images in all tissues but to a variable degree. This led to an increased contrast-to-noise ratio, particularly between fat and solid structures, and to a reduction in the contrast between fat and fluid. Artifacts were reduced in FSE sequences leading to improved image quality in 83% and increased diagnostic information in 10%. This is of particular advantage when using time consuming T2-weighted sequences, which are necessary for the examination of the female pelvis.

Adult↗

PubMed1993

[Three-dimensional imaging of the pelvic veins using magnetic resonance angiography].

The veins in the pelvis and lower limbs have been demonstrated by means of magnetic resonance angiography (MRA) in 11 normals and in 20 patients, using a "time-of-flight" technique (TOF). Using normals, changes in the measurement parameters were used in order to optimise the examination protocol; consequently, the internal and external iliac veins and the superior and inferior gluteal veins could be identified in all cases and the internal pudendal veins in 6 out of 11 cases. This examination protocol was then used in patients with clinical suspicion of lower limb or pelvic vein thrombosis. Comparison of the MRA findings with those of phlebography (7 cases), duplex sonography (6 cases) and colour Doppler examinations (11 cases) showed that MRA was better for diagnosing thrombosis of the internal iliac veins (10 cases) than the other methods. In two patients thromboses of the common iliac veins and the inferior vena cava were demonstrated which were missed by colour Doppler examination. On the basis of our present experiences, MRA, using a two-dimensional TOF technique, appears to be a reliable non-invasive technique for demonstrating the veins of the pelvis and thigh.

Adult↗

PubMed1993

[Magnetic resonance imaging. Sequences, options, indications].

In the last few years several new MR sequences have been developed an even more imaging options have become available. In this paper, the properties of all the important MR sequences and their possible variations are discussed and their use in different clinical settings is addressed.

Contrast Media↗

PubMed1992

Swollen lower extremity: role of MR imaging.

The authors assessed the use of magnetic resonance imaging in differentiating lymphedema, phlebedema, and lipedema of the lower limb. They examined 14 patients: five with lipedema, five with lymphedema, and four with phlebedema. T1- and T2-weighted transaxial sequences were performed before administration of gadolinium tetraazacyclododecane-tetraacetic acid (DOTA) and T1-weighted spin-echo sequences were performed after administration of Gd-DOTA in each patient. Images of patients with lipedema showed homogeneously enlarged subcutaneous layers, with no increase in signal intensity at T2-weighted imaging or after Gd-DOTA administration. Patients with phlebedema had areas containing increased amounts of fluid within muscle and subcutaneous fat. In lymphedema, a honeycomb pattern above the fascia between muscle and subcutis was observed, with a marked increase in signal intensity at T2-weighted imaging. After Gd-DOTA administration, there was only a slight increase in signal intensity in the subcutis in lymphedema and phlebedema and a moderate increase in signal intensity in muscle in phlebedema.

Adolescent↗