Biomedical subjects

M Heller

Publications and source records attributed to M Heller.

At least 109 records · Page 6Linked to original sources

PubMed2000

Quantitation of renal perfusion using arterial spin labeling with FAIR-UFLARE.

Quantitative perfusion imaging of human kidneys was performed using arterial spin labeling MRI with a fast spin echo readout-sequence. Perfusion maps of centrally located single slices were obtained in axial and coronal orientations. In ten healthy volunteers, the mean value of perfusion was 213+/-55 mL/(100g min) with a range from 140 to 319 mL/(100g min). These results are in accordance with literature data, considering the fact that FAIR only measures the perfusion component normal to the imaging plane. Intra-individual reproducibility errors of +/-11% were smaller than the natural interindividual variability of renal perfusion (SD = +/- 25%). Perfusion in the cortex was approximately 3-4 times higher compared to the medulla. Considering the relatively high resolution of 2x2x10 mm3, the ability to quantify perfusion, and the lack of ionizing radiation and contrast media, this technique should prove useful in diagnosing renal pathologies that are associated with reductions in tissue perfusion.

Adult↗

PubMed2000

Evaluation of water content by spatially resolved transverse relaxation times of human articular cartilage.

Non-invasive assessment of cartilage properties, specifically water content, could prove helpful in the diagnosis of early degenerative joint diseases. Transverse relaxation times T(2) of human articular cartilage (34 cartilage slices of three donors) were measured on a pixel-by-pixel basis in a clinical whole body MR system in vitro. In vivo feasibility to measure quantitative T(2) maps was shown for human patellar cartilage. The relaxation times of cartilage with collagen in the radial zone oriented perpendicular to the magnetic field increased from approximately 10 ms near the bone to approximately 60 ms near the articular surface. Cartilage water content of the tibial plateau and femoral condyles could be determined from the correlation with T(2) (R(2) = 0.71) with an error of approximately 2 wt.%. In vivo, directional variation would need to be considered. If confirmed in vivo, T(2) measurements could potentially serve as a non-invasive tool for the evaluation of the status and distribution of water content in articular cartilage.

Adult↗

PubMed2000

[Digital subtraction angiography of the extremities using step-translation technique].

PURPOSE: To evaluate, how routine application of i.a. DSA with the step-translation technique using a single contrast bolus can effectively reduce radiation exposure and the amount of contrast media in comparison to standard peripheral DSA. METHOD/MATERIALS: 100 patients with peripheral arterial occlusive disease were assessed with step-translation DSA, 100 with standard DSA using the same equipment. Imaging quality was rated two observers, judgement by consensus. Comparison of the technical data (radiation dose, contrast media) was based on pairs of patients with similar constellations of stenoses to reduce selection bias. RESULTS: Step-translation DSA was of high imaging quality from the iliac vessels to the popliteal artery. In the distal leg, imaging was often impaired by effects like unilaterally delayed contrast flow due to high grade stenosis or motion artifacts. 53% of the step translation DSA required 1 or 2, 29% more than two additional DSA runs. Including the additional runs, the average radiation exposure and the amount of contrast media (2434 cGycm2/128 ml) were comparable to those of standard DSA (2461 cGycm2/144 ml). CONCLUSIONS: Step-translation DSA provides high quality images. In routine application realization of the advantages over standard DSA such as reduction of examination times, radiation exposure and amounts of contrast media may be impaired by poorly collateralized stenoses or motion artifacts demanding additional series.

Aged↗

PubMed2000

[Mid-term follow-up after placement of the new balloon-expendable VIP-stent into the iliac arteries].

PURPOSE: To assess the effectiveness and mid-term patency of VIP balloon expandable stents in patients with iliac occlusive disease. MATERIAL AND METHODS: Between August and December 1997, 26 balloon-expandable VIP (Medtronic) stainless steel vascular stents were implanted in 19 patients with iliac occlusive disease. 22 lesions in common iliac (n = 11), external iliac (n = 5), common iliac plus contralateral external iliac (n = 1), and unilateral common and external iliac (n = 2) arteries were stented, allowing 20 limbs for assessment. There were 18 stenoses and 4 occlusions in 7 female and 12 male patients (mean age 65 years, range 45-80). RESULTS: All lesions were treated satisfactorily, yielding a technical success rate of 100%. Primary patency was 91% (20/22) at 6 months. In 2 lesions restenoses (90% and 70%) were observed, requiring repeated angioplasty. Color Doppler analysis at 12 months revealed no further restenoses. CONCLUSION: The new VIP balloon-expandable stents achieve very good initial technical success and good mid-term patency in the treatment of iliac occlusive disease.

Aged↗

PubMed2000

[First results after implantation of the new balloon-expanded Bridge-Stent into the iliac artery].

PURPOSE: To determine the success and patency rates of the new, balloon-expandable Bridge-stents for treatment of occlusions and stenoses of iliac arteries. MATERIAL AND METHODS: Between April and October 1999, 21 patients suffering from peripheral arterial occlusive disease were treated (22 lesions). In 20 cases high-grade stenoses and in two cases complete occlusions were treated. 23 balloon-expandable Bridge-stents were implanted in the common iliac (n = 16) and the external iliac (n = 6) artery after percutaneous transluminal angioplasty. RESULTS: All interventions were performed with technical success. The mean ankle-brachial index (ABI) increased from 0.7 +/- 0.19 before to 0.86 +/- 0.16 at 24 hours after the procedure (Rutherford +3 [n = 18] and +2 [n = 3]); the ABI measured after 6 months was 0.89 +/- 0.16. The primary cumulative patency rate amounted to 91% (20/22) at 6 months. In two cases restenosis of 75% were observed, requiring repeated angioplasty. CONCLUSION: The new balloon-expandable Bridge-stents achieve very good initial technical success and promising short-term patency in the percutaneous treatment of iliac occlusive disease.

Adult↗

PubMed2000

[Contrast media-enhanced 3D MR angiography before endovascular treatment of aneurysm in the abdominal aorta, iliac artery and peripheral vessels].

PURPOSE: The value of DSA for the measurement of aortic and peripheral arterial aneurysm dimensions before endovascular treatment is limited by projection effects. It was evaluated if additional gadolinium-enhanced three-dimensional MR angiography (3D-CEMRA) could compensate for the disadvantages of DSA. MATERIALS AND METHODS: 21 patients with 35 aneurysms in the abdominal aorta (14), iliac (9) and femoropopliteal vessels (12) were assessed with DSA (7 with calibrated catheter, 14 with yardstick) and 3D-CEMRA (TR/TE 7.8/2.1 ms, flip-angle 40 degrees, Matrix 512 x 224, FOV 500 mm, eff. slice 1.8 mm). We measured and compared aneurysm dimensions on both modalities. 3D-CEMRA was regarded as the reference method to evaluate the dimension of DSA-projection effects. RESULTS: Diameter and length of aneurysms were underestimated on DSA with the yardstick as reference. The deviation ranged from 15% (+/- 5%) in the aorta to 21% (+/- 10%) in the iliac vessels. Only with calibrated catheters as reference (7/21 DSA), were the distances on DSA correlated well with MRA. In 2/35 aneurysms 3D-CEMRA detected thrombosis with difference between length of inner lumen dilatation on DSA and whole aneurysm length. 2/5 accessory renal arteries found on DSA were not detected on 3D-CEMRA. CONCLUSIONS: 3D-CEMRA is a valuable adjunct to DSA for pre-interventional diagnostics of aortic and peripheral arterial aneurysms. It provides exact evaluation of aneurysm dimensions and information about partial thrombosis.

Aneurysm↗

PubMed2000

[Quantification of fluid flow in magnetic resonance tomography: an experimental study of a flow model and liquid flow measurements in the cerebral aqueduct in volunteers].

PURPOSE: To study the feasibility o MRI for quantification of fluid flow in a tube model and the cerebral aqueduct (CA) in volunteers. VOLUNTEERS AND METHODS: All studies were performed on a 1.5 T MR scanner using a head coil and a FLASH 2D phase contrast sequence with a velocity encoding at 20 cm/s. Flow (real value, ml/sec) of a saline fluid was measured in a flexible tube model with different inside diameters: 0.75-3 mm. Three flow velocities were given (normal value). To test the reproducibility, three studies were done using a flow of 0.12 or 0.14 ml/sec and a tube diameter of 0.75 and 2.0 mm. The ratio of normal to real flow value was calculated (ideal ratio = 1). MRI of CA and flow quantification was done in 24 volunteers (28 +/- 4 years). RESULTS: Using tubes with a diameter of 0.75 and 1.5 mm the real flow was sometimes higher than the velocity encoding of the phase contrast sequences. Because of this measurements of the fluid flow and the flow velocities were impossible. There was agreement for fluid flow quantification in the tube of 3.0 mm and high agreement in the tube of 2.0 mm in diameter with reproducible results. The mean diameter of the CA in normal subjects was 2.0 +/- 0.3 mm, the mean cerebral flow was 0.04 +/- 0.02 ml/sec and the peak velocity 3.06 +/- 1.59 cm/sec. CONCLUSIONS: Reliable flow quantification with MRI is feasible if the diameter of the lumen is greater than 1.5 mm, and if the flow velocity is lower than the velocity encoding. In cases of smaller diameters and higher flow velocities the velocity encoding has to be changed. Because of this the quantification seems to be inaccurate in cases of aqueductal stenosis with the method we used.

Adult↗

PubMed2000

Intravascular ultrasound evaluation of peripheral arterial stent-grafts.

RATIONALE AND OBJECTIVES: To evaluate neointimal hyperplasia, plaque distribution, and morphologic features of peripheral arterial stent-grafts with intravascular ultrasound (IVUS). METHODS: Twenty-three patients with stenoses or occlusions of the pelvic or femoral arteries were treated with 31 stent-grafts. Angiography and IVUS of the stented artery were performed 13.9 +/- 9.7 months after stent implantation. Maximum in-stent restenosis was measured by IVUS. Plaque composition and lesion topography were also assessed. RESULTS: The maximum in-stent restenosis was 53.2 +/- 26.5% for the femoral and 14.2 +/- 10.1 for pelvic arterial stent-grafts. Predilection sites of maximum neointimal tissue accumulation were the edges of the femoral stent-grafts. Only small amounts of neointimal hyperplasia were found in the stent-graft edges. No predilection site for maximum in-stent restenosis was found for the pelvic arterial stent-grafts. CONCLUSIONS: Predilection sites of maximum in-stent restenosis were the edges of femoral stent-grafts in contrast to pelvic stent-grafts. Femoral stent-grafts showed significantly higher graded stenoses with IVUS than iliac stent-grafts. The authors' findings at IVUS did not change the treatment plan in these patients treated with stent-grafts.

Arterial Occlusive Diseases↗

PubMed2000

Rheolytic hydrodynamic thrombectomy for percutaneous treatment of acutely occluded infra-aortic native arteries and bypass grafts: midterm follow-up results.

RATIONALE AND OBJECTIVES: To evaluate the efficacy of a rheolytic thrombectomy catheter (RTC) for treatment of acutely occluded infra-aortic native arteries and bypass grafts and to determine midterm primary patency, death, and amputation-free survival rates. METHODS: From March 1995 to September 1997, 112 patients with occluded arteries or bypass grafts were primarily treated with RTC at two centers. Thrombus removal was evaluated by two angiographers. RESULTS: More than 75% of the thromboembolic material could be removed with RTC alone. Mean activation time of RTC was 280 +/- 163 seconds. Residual mural or organized thrombi (29%) required adjunctive fibrinolytic therapy or aspiration thrombectomy. Remaining stenoses were treated with percutaneous transluminal angioplasty and additional stent implantation. For acute reocclusions, surgical intervention was required. Technical success after the entire procedure was 88.4%. RTC-associated complications included distal embolization, dissection, vessel perforation, and technical failure of RTC. Mean follow-up time was 14.8 months +/- 11.5, rates of primary patency, secondary patency, death, and amputation-free survival were 60%, 84%, 16%, and 75% after 2 years, respectively. CONCLUSIONS: RTC is a rapid and efficient technique for mechanical thrombectomy of acutely thrombosed native leg arteries and bypass grafts. Midterm results are comparable to the results of alternative treatment modalities such as Fogarty balloon thromboembolectomy or local fibrinolysis.

Aged↗

PubMed2000

Mechanical thrombectomy of acute thrombosis in transjugular intrahepatic portosystemic shunts.

RATIONALE AND OBJECTIVES: To evaluate the feasibility of mechanical thrombectomy with the use of the Amplatz thrombectomy device (ATD) in restoring patency to acutely thrombosed stent-shunts after transjugular intrahepatic portosystemic shunt (TIPS) placement. METHODS: Mechanical thrombectomy with the ATD was performed in 10 consecutive patients with angiographically documented complete thrombosis of the stent-shunt (mean +/- SD, 6.6 +/- 3.4 cm), which occurred an average of 2.8 months (range, 0-11 months) after the TIPS procedure. RESULTS: In all patients, immediate restoration of patency of the stent-shunt was achieved after thrombectomy alone (n = 1), thrombectomy plus percutaneous transluminal angioplasty (PTA; n = 4), and thrombectomy, PTA, and stenting (n = 5). The mean activation time of the ATD was 253 +/- 43 seconds. The pressure gradient for portal decompression decreased from 23 +/- 6 mmHg before to 11 +/- 3 mmHg after the procedure. The primary patency rate was 80% at 3 months and 60% at 11 months. CONCLUSIONS: Mechanical thrombectomy with the ATD in acutely thrombosed TIPS is technically feasible. Mechanical thrombectomy is a potential alternative to thrombolysis.

Adult↗

PubMed2000

Characterization of ultrasmall magnetite [correction of paramagnetic magnetite] particles as superparamagnetic contrast agents in MRI.

RATIONALE AND OBJECTIVES: Very small dextran-coated magnetite particles were developed. These particles can be used either as immunospecific contrast agents for MRI by coupling to antibodies or as an interstitial contrast agent. METHODS: The particles were synthesized from iron chloride/dextran solutions. Size was evaluated by electron microscopy and photon correlation spectroscopy. The iron concentration was determined by x-ray spectroscopy. T1 and T2 values as well as relaxivities RI and R2 were evaluated with a clinical MR scanner at 1.5 T. Biocompatibility assays were performed with the cell line U937 in methylcellulose cultures. RESULTS: Superparamagnetic, dextran-coated magnetite particles with a hydrodynamic diameter of 10 nm were developed. The iron core size was 7 nm; R1,7 L/mmol x s; and R2, 19 L/mmol x s. These particles are smaller than those currently available commercially and therefore show a smaller R1 to R2 ratio. Biocompatibility tests have shown no toxic side effects so far. CONCLUSIONS: Ultrasmall magnetite particles with a dextran coating were developed; the physical properties of these particles evaluated in vitro are described in this study.

Cell Count↗

PubMed2000

Metabolically active components of fat free mass and resting energy expenditure in nonobese adults.

Resting energy expenditure (REE) and components of fat-free mass (FFM) were assessed in 26 healthy nonobese adults (13 males, 13 females). Detailed body composition analyses were performed by the combined use of dual-energy X-ray absorptiometry (DEXA), magnetic resonance imaging (MRI), bioelectrical impedance analysis (BIA), and anthropometrics. We found close correlations between REE and FFM(BIA) (r = 0.92), muscle mass(DEXA) (r = 0.89), and sum of internal organs(MRI) (r = 0.90). In a multiple stepwise regression analysis, FFM(BIA) alone explained 85% of the variance in REE (standard error of the estimate 423 kJ/day). Including the sum of internal organs(MRI) into the model increased the r(2) to 0.89 with a standard error of 381 kJ/day. With respect to individual organs, only skeletal muscle(DEXA) and liver mass(MRI) significantly contributed to REE. Prediction of REE based on 1) individual organ masses and 2) a constant metabolic rate per kilogram organ mass was very close to the measured REE, with a mean prediction error of 96 kJ/day. The very close agreement between measured and predicted REE argues against significant variations in specific REEs of individual organs. In conclusion, the mass of internal organs contributes significantly to the variance in REE.

Absorptiometry, Photon↗

PubMed2000

Magnetic resonance arthrography of the acetabular labrum. Macroscopic and histological correlation in 20 cadavers.

We studied the sensitivity and specificity of magnetic resonance arthrography (MRa) for the diagnosis of lesions of the acetabular labrum in 20 cadaver hips. The MRa results were compared with macroscopic and histological findings. We found that the labrum could be satisfactorily delineated by MRa and that large detachments could be identified satisfactorily. The diagnosis of small detachments and degeneration of the labrum was less reliable.

Acetabulum↗

PubMed2000

A new method for quantitative ultrasound measurements at multiple skeletal sites: first results of precision and fracture discrimination.

We investigated a new multisite quantitative ultrasound device that measures the acoustic velocity in axial transmission mode along the cortex. Using a prototype of the Omnisense (Sunlight Ultrasound Technologies, Rehovot, Israel), we tested the performance of this instrument at four sites of the skeleton: radius, ulna, metacarpal, and phalanx. Intraobserver (interobserver) precision errors ranged from 0.2% to 0.3% (0.3% to 0.7%) for triplicate measurements with repositioning. Fracture discrimination was tested by comparing a group of 34 women who had previously suffered a fracture of the hip, spine, ankle, or forearm to a group of 28 healthy women who had not suffered a fracture. Age-adjusted standardized odds ratios ranged from 1.6 to 4.5. Except for the ulna the sites showed a significant fracture discrimination (p < 0.01). The areas under the receiver operating curves (ROC) curves were from 0.88 to 0.89 for radius, metacarpal, and phalanx. A combination of the results from the three sites showed a significant increase of the ROC area to 0.95 (p < 0. 05). Our results show promising performance of this new device. The ability to measure a large variety of sites and the potential to combine these measurements are promising with regard to optimizing fracture risk assessment.

Aged↗

PubMed2000

Does diving damage the brain? MR control study of divers' central nervous system.

PURPOSE: To evaluate the prevalence of cerebral white matter changes on MR imaging in healthy elderly compressed air divers with a long diving history in comparison with control subjects who have never dived. MATERIAL AND METHODS: The investigation employed 59 experienced elderly divers and 48 control subjects matched for age, body mass index, alcohol and smoking history. MR studies included a fluid attenuated inversion recovery sequence and T1- and T2-weighted pre- and postcontrast images in axial orientation of the whole brain to localize white matter changes. RESULTS: MR images did not show any morphologic abnormalities in the brains of divers. Both groups - divers and controls - did not differ significantly with respect to white matter changes of the brain. CONCLUSION: No increased prevalence of cerebral white matter changes in compressed air divers compared with a healthy worker sample of similar age were found. Thus, extensive compressed air diving may not necessarily be related to radiological changes on MR.

Adult↗

PubMed2000

[Quantitative ultrasonic diagnosis for the assessment of osteoporosis].

In recent years Quantitative Ultrasound (QUS) approaches have increasingly been used for the assessment of osteoporosis. Extensive study results exist for the estimation of osteoporotic fracture risk. Also, results exist for the analysis of properties which characterize osteoporosis--low bone mass and deterioration of bone architecture. However, the existence of different methods, devices and parameters has to be taken into account. Moreover, the status of the evaluation is different for each type of device. Measures of quality assurance and in-depth knowledge about limitations of the approach are of substantial importance for clinical use. Because of the lack of ionising radiation and their lower cost, QUS approaches--if used appropriately--can play an important role in the assessment of osteoporotic fracture risk.

Bone Density↗

PubMed1999

Analysis of membrane proteins by two-dimensional electrophoresis: comparison of the proteins extracted from normal or Plasmodium falciparum-infected erythrocyte ghosts.

Parasite-encoded membrane proteins translocated to the surface of infected erythrocytes or in specialized vesicles underneath (Maurer's clefts) play a key role in the asexual life cycle of Plasmodium falciparum (a malaria-causing protozoan), by mediating key steps such as red blood cell invasion, sequestration of infected cells in microcapillaries, and red blood cell rupture. A large-scale analysis of these membrane proteins would therefore be of great help to gain knowledge of the different stages of the Plasmodium falciparum life cycle. In order to be able to detect and identify parasite-encoded proteins directed to the red blood cell membrane, we first defined the conditions required for optimal extraction and separation of normal red blood cell ghost proteins by two-dimensional gel electrophoresis. These conditions included the use of urea, thiourea and new zwitterionic detergents in the extraction and isoelectric focusing media. The optimized conditions were then applied to analyze normal and P. falciparum-infected red blood cell ghosts. Several protein spots were found only in infected ghosts and are expected to represent parasite-encoded proteins. These proteins are currently under investigation.

Animals↗

PubMed1999

Enhancement of Mycoplasma bovis detection in milk samples by antigen capture prior to PCR.

A rapid and sensitive procedure to detect Mycoplasma bovis from milk samples was developed. Mycoplasma cells were collected by selective binding to a monoclonal antibody, thus separating them from milk proteins and facilitating DNA extraction. Polymerase chain reaction (PCR) using species-specific primers allowed detection of 20 cfu ml-1 in agarose gels and 2 cfu ml-1 on Southern blots. The method is especially suitable for specimens from subclinical cases and intermittent shedders.

Animals↗