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M Boos

Publications and source records attributed to M Boos.

12 recordsLinked to original sources
PubMed1999

Phase-contrast MR angiography of peripheral arteries: technique and clinical application.

This articles describes Phase-Contrast-MRA (PC-MRA) techniques and their current clinical applications for peripheral arteries based on more than 250 clinical MRA studies performed at two institutions. PC-MRA depends on phase shifts caused by blood flow and thus this technique permits the use of coronal or sagittal slice orientations with large FOV's along the direction of the vessel of interest. Clinical applications focus on patients with peripheral arterial occlusive disease (PAOD) describing the role and limitations of PC-MRA for the work-up of stenoses, occlusions, aneurysms, and postsurgical follow-up. Recommendations for clinical routine are provided. A combined MR angiographic approach with various MRA techniques depending on the vessel segment to be imaged, PC-flow velocity measurements, and high-resolution scans of the vessel wall may turn out to be diagnostically effective and provide a comprehensive test for PAOD within the near future.

Aneurysm↗
PubMed1999

Selection of patients for carotid thromboendarterectomy: the role of magnetic resonance angiography.

It has been shown in clinical trials that patients with high grade symptomatic carotid stenosis benefit from carotid thromboendarterectomy. Because of the invasiveness and the costs of intra-arterial digital subtraction angiography, the current standard of reference for the grading of carotid stenosis, magnetic resonance angiography, has become a technique of utmost interest for evaluation of the carotid arteries. The time-of-flight and the newly developed contrast-enhanced magnetic resonance angiography techniques are discussed. At present, we recommend computer enhanced magnetic resonance angiography for screening procedures and for the post-operative follow-up. For pre-operative evaluation we still recommend intra-arterial digital subtraction angiography.

Angiography, Digital Subtraction↗
PubMed1998

Pulmonary circulation.

Evaluation of the pulmonary vasculature is mainly indicated in patients with suspected pulmonary thromboembolism. The routine procedure so far is ventilation-perfusion scintigraphy alone or in combination with diagnostic assessment of the legs to rule out deep venous thrombosis. The results are still not reliable for the majority of patients. In the case of equivocal diagnosis, invasive conventional angiography is considered the gold standard. With steady improvements in tomographic imaging techniques, such as computed tomography (CT) or magnetic resonance imaging (MRI), non-invasive alternatives to the routine diagnostic work-up are given. Helical CT and CTA techniques are already in clinical use and estimated to sufficiently serve the demands for detection/exclusion of pulmonary thromboembolism. The disadvantages mainly concern peripheral disease and reconstruction artifacts. MRI and MR angiography have been implemented in the diagnosis of pulmonary vascular disease since the introduction of contrast-enhanced MRA. In breath-hold techniques, the entire lung vascularization can be delineated and thromboemboli can be detected. The clinical experience in this field is limited, but MRI has the potential to demonstrate its superiority over CT due to its improved delineation of the vascular periphery and the more comprehensive three-dimensional reconstruction.

Aged↗
PubMed1998

Contrast-enhanced magnetic resonance angiography of peripheral vessels. Different contrast agent applications and sequence strategies: a review.

In this article the relation between contrast medium (CM) application and sequence parameters will be discussed with respect to clinical use of the contrast-enhanced magnetic resonance angiography (CE-MRA) in the peripheral vessel region. The adjustment of the sequence parameters, the CM application timing and the bolus geometry is necessary for an effective use of CE-MRA. Investigation protocols for several vascular regions differ mainly corresponding to varying fields of view and slab thickness. Restrictions of increasing the measurement time are expected in peripherally localized vessels if fast arteriovenous transit time occurs. The vessel contrast depends from (1) optimal CM bolus timing and (2) bolus geometry defined by the parameters of the intravenous bolus injection (flow rate, dose and NaCl flush volume). Our study results have shown that the bolus remains compact but also shorter if a higher flow rate is being applied at equal dose. The enlargement of the NaCl flush volume has evidently caused an increased intraarterial CM concentration and a slightly bolus lengthening. The exact timing regimen requires an automated mechanical CM injection pump. In most countries, a total dose of 0.3 mmol/kg Gd is allowed for application during one investigation. Therefore, obtaining an angiogram of the entire iliac and leg region this total dose must be separated. 0.1 mmol/kg for each of the three measurements can be recommended. Otherwise, using this lower CM dose results in less spatial resolution. At least a dosage of 0.2 mmol/kg Gd is necessary to achieve a higher spatial resolution. The calculation of CM dosage should be also related to the dedicated vessel region of interest than to the body weight only.

Arterial Occlusive Diseases↗
PubMed1997

Clinical utility of contrast-enhanced MR angiography.

MR angiography (MRA) is a technique under ongoing discussion. Its non-invasiveness and sensitivity to flow irregularities make it an investigational technique which is easy to apply but which does not always lead to comprehensive results. It requires special skill to perform and also experience for correct interpretation of the results. The lengthiness of the procedure combined with certain physical properties tends to limit its use to mostly neurovascular applications. With the introduction of ultrafast MRA in conjunction with peripheral bolus-injection of extracellular contrast media, a new approach to the imaging of such regions as the thoracic and abdominal vasculature not to mention other vascular territories has become possible. In this paper, considerations of bolus and measurement optimization and timing protocols for dedicated indications are presented together with an overview on the experience acquired to date for CE-MRA of the carotid artery, mediastinal and pulmonary vessels, abdominal vasculature, and peripheral vessels. The main advantage of ultrafast CE-MRA is that patients are subjected to much more tolerable breath-hold investigations with the result that physiological motion such as peristalsis or major pulsation is minimised.

Adolescent↗
PubMed1997

[Conventional magnetic resonance angiography and contrast enhanced magnetic resonance angiography of extracranial blood vessel segments].

The introduction of fast gradient systems allows a reliable visualization of the extracranial carotid vessels by the magnetic resonance angiography (MRA) which meanwhile is implemented into clinical routine. By the mainly applied time-of-flight (TOF) technique, vessels can be imaged without contrast agent (CA). Due to the application of ultra-fast gradient-echo-sequences, the first-pass evaluation of an intravenous bolus-injection of Gadolinium in the carotids from the aortic arch up to the skull base can be performed in less than 30 s. In this study. Advantages and disadvantages of both techniques are discussed. For a qualitatively optimal contrast enhanced MRA (CE-MRA) timing parameters like injection delay, flow rate and the adjustment of sequence parameters have to be considered in relation to the fast venous return from the sinus to the jugular veins. First, the optimal time point of the data acquisition have been determined at a model and with a computer simulation in reference to the presence of CA in the arteries. As a result, 90% of the contrast contribution is defined by 16% of the symmetrically acquired central k-space lines. A measuring protocol for clinical use was obtained by a gradual variation of spacial resolution, measuring time and CA-injection parameters and was proved in normal volunteers and patients. An exact determination of the bolus-arrival-time by means of a test-bolus injection was acquired. The best qualitative results were achieved by a double-dose- injection at 2 ml/s injection rate. The temporal reserves of ultra-fast sequences should be invested in the improvement of the spatial resolution. To date, further investigations related to the problem of optimal CA-application may improve the potentials of CE-MRA procedures.

Carotid Arteries↗
PubMed1997

[MR angiography of thoracic blood vessels].

Through the introduction of newly invented high-performance gradient systems to MRI, which enable for echoplanar imaging (EPI), also magnetic resonance angiography (MRA) has gained an entirely new field of applications and techniques. Ultrafast imaging techniques in MRA allow the investigation of larger vascular areas within a single breath-hold-period. Artifacts like motion induced signal misregistrations, dephasing or saturation of the vascular signal are minimized by extremely short echo times. The technique thus requires the intravenous application of a contrast media bolus, usually a gadolinium compound, which is in standard clinical use. Coordination of the bolus injection and the timing of the data acquisition is crucial for optimal results. The first pass evaluation of the contrast media resembles CTA to a certain extend. Due to the fast measurement and the high contrast in contrast-enhanced MRA (CE-MRA) new applications and indications are developed like MRA of the pulmonary vessels. The paper offers considerations and trials for optimization of thoracical CE-MRA. Besides parameter constellation also bolus-optimization is described with respect to the dedicated anatomical premises. Investigations on volunteers and on patients build a basis for suggestions of optimized CE-MRA procedures. To date, a final estimation of the clinical value of the new technique cannot be given since ongoing improvements change the optimal protocol frequently and the potential of further developments is high.

Adolescent↗
PubMed1997

[Phase-contrast MR angiography of the lower extremity. Comparison of methods and clinical application].

PURPOSE: To investigate whether phase-contrast MRA is a clinically suited approach to examine arteries of the pelvis and lower extremities. METHODS: The study was divided into two parts, a volunteer study and patient study. Three MRA techniques-2D TOF with venous saturation, 3D magnitude contrast and 2D phase contrast with ECG triggering-were intraindividually compared in 15 volunteers and evaluated by three blinded readers. Subsequently, a total of 230 vessel segments of 45 MRA studies using ECG-triggered phase contrast were compared with intraarterial DSA. All vessel segments were scored by three blinded readers using a five-point scale with DSA serving as the gold standard. RESULTS: ECG-triggered phase contrast provided better image quality than the other MRA techniques as assessed by the Friedman test. Clinical studies demonstrated a significant correlation of DSA and MRA as assessed by the Spearman correlation and kappa statistics for individual readers. CONCLUSION: MRA of the pelvis and lower extremities may be performed with 2D ECG-triggered phase-contrast MRA within a reasonable time frame (< 30 min). MRA slabs provide orientation similar to that with DSA projections and good to very good correlation of vessel pathology as shown by kappa statistics.

Angiography, Digital Subtraction↗
PubMed1995

[Magnitude contrast angiography in peripheral arterial occlusive disease of the lower extremities].

PURPOSE: To assess the clinical value of magnitude contrast angiography in arteriosclerosis of the lower limb. MATERIAL AND METHODS: 187 examinations were done in 105 patients with arteriosclerotic lesions of the femoropopliteal vessels. The MRA results were compared to DSA and conventional angiography. 36 patients were investigated before and after angioplasty. RESULTS: Occlusions were detected correctly in all cases. In mild and moderate stenoses there was 90% agreement. High-grade stenoses may simulate occlusions. All interruptions of the signal with a length of 1 to 10 mm have to be read as high-grade stenoses (MRA sensitivity was 0.96 and specificity 0.94). In patients with low cardiac output MRA may be advantageous in comparison to DSA: collaterals and vessels distal to occlusions were visualized better in MRA. Axial scans show morphology of stenoses and occlusions and influenced the choice of treatment in 6 cases. In 3 cases, thrombotic material and calcified plaque were distinguished. After angioplasty vessel wall lesions such as dissection of the intima or compressed plaque inside the vessel wall were well visualized. Agreement was 92% with MRA as opposed to lesser values with DSA.

Angiography, Digital Subtraction↗
PubMedDate not supplied

Goretex fabric as a cast underliner in children.

The efficacy of using Goretex fabric as a cast liner to improve skin care was evaluated. A prospective study was performed of 20 patients undergoing casting using Goretex underliners. At each cast change or at the end of casting, skin condition was evaluated. No change in any standard treatment protocol regarding cast changes was made because of the Goretex liner. Goretex fabric provided improved ease of care and prevented cast soiling. The breathability of the fabric was believed to be a benefit in decreasing skin irritation.

Casts, Surgical↗