Biomedical subjects

M F Reiser

Publications and source records attributed to M F Reiser.

At least 37 records · Page 2Linked to original sources

PubMed2005

Techniques for diffusion-weighted imaging of bone marrow.

Diffusion-weighted magnetic resonance imaging (DWI) is an imaging technique which is sensitive to random water movements in spatial scales far below those typically accessible by magnetic resonance imaging (MRI). This property makes DWI a powerful tool for diagnosis of diseases which involve alterations in water mobility, such as acute stroke. In bone marrow, DWI has been proven to be a highly useful method for the differential diagnosis of benign and malignant compression fractures. Unfortunately, the application of DWI sequences to the bone marrow frequently suffers from artifacts, which in some cases seriously restrict the diagnostic utility of the image. This requires the introduction of additional correction techniques, or even the development of new sequences. Thus, the selection of an adequate imaging technique for DWI of the bone marrow is a very important issue. In this article the most important sequences for DWI of the bone marrow are reviewed. Special attention is paid to the problems associated with these sequences, as well as their possible solutions.

Artifacts↗

PubMed2005

Whole-body MR imaging of bone marrow.

In clinical routine, multimodality algorithms, including X-ray, computed tomography, scintigraphy and MRI, are used in case of suspected bone marrow malignancy. Skeletal scintigraphy is widely used to asses metastatic disease to the bone, CT is the technique of choice to assess criteria of osseous destruction and bone stability. MRI is the only imaging technique that allows direct visualization of bone marrow and its components with high spatial resolution. The combination of unenhanced T1-weighted-spin echo- and turbo-STIR-sequences have shown to be most useful for the detection of bone marrow abnormalities and are able to discriminate benign from malignant bone marrow changes. Originally, whole-body MRI bone marrow screening was performed in sequential scanning techniques of five body levels with time consuming coil rearrangement and repositioning of the patient. The introduction of a rolling platform mounted on top of a conventional MRI examination table facilitated whole-body MR imaging and, with the use of fast gradient echo, T1-weighted and STIR-imaging techniques, for the first time allowed whole-body imaging within less than one hour. With the development of parallel imaging techniques (PAT) in combination with global matrix coil concepts, acquisition time could be reduced substantially without compromises in spatial resolution, enabling the implementation of more complex and flexible examination protocols. Whole-body MRI represents a new alternative to the stepwise multimodality concept for the detection of metastatic disease, multiple myeloma and lymphoma of the bone with high diagnostic accuracy.

Bone Marrow Neoplasms↗

PubMed2005

[Estimation of diffuse bone marrow infiltration of the spine in multiple myeloma: correlation of MRT with histological results].

PURPOSE: To determine the detection of diffuse bone marrow infiltration with MRI in comparison with histopathological findings. MATERIALS AND METHODS: MRI was performed on 45 patients with histologically proven multiple myeloma and on 30 healthy individuals. Three experienced radiologists read separately Tl-weighted SE sequences, STIR sequences and the combination of Tl-weighted SE and STIR sequences of the spine. Additionally, Tl-weighted SE sequences were obtained after gadolinium administration and the percentage increase in signal intensity was calculated. Bone marrow histology was used as gold standard for assessing the grade of infiltration. A dichotomous decision (infiltration yes/no) was made when assessing the MRI examinations. RESULTS: For the visual detection of diffuse infiltration, the best sensitivity was found with Tl-weighted SE sequences, achieving 71 % on average. The specificity was 89 %. The STIR sequences showed a sensitivity of 61 % and a specificity of 98 %, and the combination of Tl-weighted/STIR-sequences achieved a sensitivity of 65 % and a specificity of 94 %. In comparison with the histological findings, the sensitivity of the Tl-weighted sequences was 35 % for low-grade, 89 % for moderate and 100 % for high-grade infiltration. The application of contrast material with calculation of the percentage signal increase improved the detection by 7 %. CONCLUSION: The sensitivity of the visual detection of diffuse multiple myeloma with unenhanced MRI is limited for low-grade or moderate infiltration, whereas the sensitivity for high grade infiltration is reliable. The specificity is high and the diagnostic confidence improves after application of contrast material with calculation of the percentage increase in signal intensity.

Adult↗

PubMed2005

The feasibility of spatial high-resolution magnetic resonance angiography (MRA) of the renal arteries at 3.0 T.

PURPOSE: To evaluate the feasibility of high-spatial resolution magnetic resonance angiography (MRA) of the renal arteries at 3.0 T. MATERIAL AND METHODS: Twelve healthy volunteers (mean age, 38.8 years) underwent renal MRA at 3.0 T. The application of parallel imaging with an acceleration factor of 3 allowed obtaining MR angiographic data with a voxel size of 0.9 x 0.8 x 0.9 mm in scan time of only 16 s. A dose of 0.2 mmol/kg body weight of 0.5-molar gadodiamide was administered at a flow rate of 2 ml/s. For image analysis, image quality, presence of artifacts, venous contamination and level of noise were rated by two radiologists in consensus. RESULTS: All examinations were of diagnostic quality. The image quality was rated good or very good in 91 % (11/12) of cases. Due to the high parallel imaging factor the level of noise was slightly increased without diagnostic impairment. Mild venous enhancement was found in 75 % (9/12) of the examinations. CONCLUSION: Renal MRA at 3.0 T is feasible with high spatial resolution and a short acquisition time.

Adult↗

PubMed2005

Analysis and correction of ballistocardiogram contamination of EEG recordings in MR.

PURPOSE: To examine the influence of cardiac activity-related head movements and varying blood pulse frequencies on the shape of electroencephalography (EEG) recordings in a high magnetic field, and to implement a post-processing technique to eliminate cardiac activity-related artifacts. MATERIAL AND METHODS: Respiratory thoracic movements, changes of blood pulse frequency and passive head movements of 20 healthy subjects were examined outside and inside an MR magnet at rest in a simultaneously recorded 21-channel surface EEG. An electrocardiogram (ECG) was recorded simultaneously. On the basis of the correlation of the left ventricular ejection time (LVET) with the heart-rate, a post-processing heart-rate dependent subtraction of the cardiac activity-related artifacts of the EEG was developed. The quality of the post-processed EEG was tested by detecting alpha-activity in the pre- and post-processed EEGs. RESULTS: Inside the magnet, passive head motion but not respiratory thoracic movements resulted in EEG artifacts that correlated strongly with cardiac activity-related artifacts of the EEG. The blood pulse frequency influenced the appearance of the cardiac activity-related artifacts of the EEG. The removal of the cardiac activity-related artifacts of the EEG by the implemented post-processing algorithm resulted in an EEG of diagnostic quality with detected alpha-activity. CONCLUSION: When recording an EEG in MR environment, heart rate-dependent subtraction of EEG artifacts caused by ballistocardiogram contamination is essential to obtain EEG recordings of diagnostic quality and reliability.

Adult↗

PubMed2004

[Evaluating multislice computed tomography for imaging coronary atherosclerosis].

PURPOSE: The purpose of this study was the evaluation of multidetector-row computed tomography (MDCT) for the assessment of atherosclerotic coronary artery vessel wall changes. METHODS: In an ex vivo study, 17 human hearts were scanned with MDCT and results were compared to histopathology. Morphologic imaging criteria of MDCT for various plaque-types were developed. In a following in vivo study, 94 coronary MDCT angiograms (MDCTA) of patients with suspected coronary artery disease (CAD) were reviewed retrospectively, assessing the diagnostic value of the coronary MDCTA, and determining the number and correlations of the various plaques types as described in the ex vivo study. Additionally, volumetry of calcified and noncalcified plaque components was performed. RESULTS: In the ex vivo study, MDCT showed a high sensitivity for calcified and non-calcified plaques. Comparing the results with histopathology, characteristic image criteria could be determined for lipid-rich, fibrous and calcified plaque components. Reviewing the contrastenhanced in-vivo MDCT coronary angiographies, presence of noncalcified plaques was proven in 38% of the patients. In 5 patients with a calcium score of 0, presence of coronary atherosclerosis was proven in the contrastenhanced scan. CONCLUSIONS: MDCT is able to differentiate various plaque components in an ex vivo setting as well as invivo. Contrastenhanced MDCT of the coronary arteries allows for the detection of noncalcified plaques. In vivo volumetry of noncalcified plaques is feasible.

Adult↗

PubMed2004

[Indications for multislice CT angiography of coronary arteries].

INTRODUCTION: The newest generation of 16-detector-row CT allows displaying the anatomy and assessment of coronary artery disease (CAD) when slow regular sinus rhythm is present. METHODS: For morphological assessment of cardiac structures by using Multi-detector row CT a dedicated scan protocol is obligatory. The indication for coronary CT angiography (CTA) is currently under investigation by several study groups. RESULTS: Because of the limited spatial and temporal resolution and coronary calcium artefacts, it is not possible with multislice CT angiography to assess coronary arteries in patients with established coronary artery disease. The anatomy of the coronary arteries can well be displayed with this technique. CONCLUSION: The high negative predictive value of coronary CTA may justify the investigation of symptomatic patients with intermediate pretest probability of CAD. Moreover coronary CTA is suitable for patients for displaying the origin and course of abnormal coronary arteries.

Artifacts↗

PubMed2004

[Determining myocardial viability in myocardial infarct. Comparison of single and multisclice MRI techniques with TurboFlash and TrueFISP sequences].

PURPOSE: The aim of the study was to compare the diagnostic accuracy in imaging viability of the myocardium with a multislice inversions recovery 2D single shot TrueFISP sequence and an established inversion recovery TurboFlash sequence. MATERIAL AND METHODS: Twelve patients with myocardial infarction were examined at a 1.5 tesla MR system (Sonata, Siemens, Medical Systems) 10 min after application of a single dose multihance (0,1 mmol/kg body weight) with a 2D multislice technique (inversion recovery single shot TrueFISP), that allows to image the entire short axis during one breathhold and a 2D single slice technique (inversion recovery TurboFlash), that requires one breathhold per slice. Signal intensity was determined in normal myocardium, in the infarcted myocardium and in the left ventricle. The contrast/noise ratio of normal and infarcted myocardium was determined. The areas of hyperintense infarction were compared for both sequence techniques. RESULTS: The multislice single shot 2D IR-TrueFisp sequence has a lower contrast/noise ratio than the IR-TurboFlash sequence (mean values 6.9 vs. 12.5) for viable and non viable myocardium. The assessment of the volume of the infarction is possible with excellent correlation of both techniques (r=0.97, p <0.036). In addition, an assessment of the transmural extent of the infarction is possible with identical spatial resolution. CONCLUSION: The inversions recovery 2D single shot TrueFisp technique allows for accurate detection of the infarction, for accurate determination of the area of the infarction and for assessment of the transmural extent of the infarction with high spatial resolution.

Adult↗

PubMed2004

[ECG-gated bypass CT angiography--application in imaging arterial bypasses].

Nowadays coronary artery bypass grafting is increasingly performed using arterial grafts. Purpose of the study was the evaluation of a appropriate 16 detector-row CT angiography protocol in patients after predominantly arterial bypass grafting. Fourteen patients after bypass grafting were including into the study and CT angiography carried out in the early postoperative period using a 16 detector-row CT system. To reduce cardiac pulsation artifacts data acquisition was implemented using ECG-gating algorithms. Overall 43 grafts (37 arterial, 6 venous) were examined. In 13 patients surgery had been performed using composite grafts with T or TY configuration. The mean heart rate was 74.1 bpm and showed a negative correlation to the image quality (r=-0.65; p=0.01). However, all data sets were diagnostic. Contrast injection protocol allowed for a homogeneous opacification throughout the vessels of interest. All non-delineationable grafts (5) showed a close proximity to the heart (T or Y grafts). Cardiac surgery is increasingly focusing on arterial revascularisation in bypass grafting and therefore leading to new demands for non-invasive bypass graft imaging. 16 detector-row CT allows a reliable visualization of even composite arterial grafts. However, for detection of grafts in the proximity of the heart a reduction of the heart rate (<65-70) still seems to be necessary.

Aged↗

PubMed2004

[Determining global heart function with real time TrueFISP in one respiratory cycle].

Real-time multislice cine techniques lead to inaccurate results in ventricular volumes based on limited temporal resolution. The purpose of the study is to evaluate a real-time cine technique with parallel imaging algorithms in comparison to standard segmented techniques. Twelve patients underwent cardiac cine MRI using real-time multislice cine trueFISP. Temporal resolution was improved using parallel acquisition techniques (iPAT) and data acquisition was performed in a single breath-hold along the patients' short axis. Evaluation of EDV, ESV, EF and myocardial mass was performed and results compared to a standard segmented single-slice cine trueFISP. Combination of real-time cine trueFISP and iPAT provided a temporal resolution of 48 ms. Results of the multislice approach showed an excellent correlation to standard single-slice trueFISP for EDV (0.94, p <0.001), ESV (0.97, p <0.001) EF (0.99, p <0.001) and myocardial mass (0.93, p <0.001). No significant differences could be found. The use of parallel acquisition techniques (PAT) allow for a substantial improvement of temporal resolution in real-time cine MRI (<50 ms). Therefore these techniques enable an accurate and exact quantification of global ventricular function.

Algorithms↗

PubMed2004

[Radiofrequency ablation of lung tumors and -metastases].

BACKGROUND AND PURPOSE: Radiofrequency ablation is increasingly used to treat tumors "beyond the liver". The aim of this article is to perform a structured and critical review of the current literature concerning RFA of the lung and to compare these results with our own experience. MATERIAL AND METHODS: 16 patients with tumors or metastases of the lung were treated in our institution within 18 months. 8 of these 16 patients were treated in a multicenter trial. For this article we compared our results to the results of all publications concerning RFA of the lung since 1995. RESULTS: 8 of our 16 patients were not included in the international multicenter trial and were followed-up at least 15 months. Within this observation period, 2 of 8 patients had recurrence of the tumors while in 6 patients no recurrence was detected. Lee et al. published a study with 30 patients. In 10 of these 30 patients RFA was performed in a curative intention with a therapeutical success in 8 of 10 patients after one year. DISCUSSION: Radiofrequency ablation of lung tumors smaller than 3 cm appears to be an alternative to surgical removal. Moreover, RFA offers a higher quality of life for the patients due to a low morbidity and mortality. However, more studies with longer observation periods are necessary for a definite conclusions.

Catheter Ablation↗

PubMed2004

[RFA of bone and soft tissue tumors].

Radiofrequency ablation (RFA) of primary and secondary liver malignancies is a promising and rapidly evolving technique, which increasingly gains importance. A new field of RFA is the minimal invasive therapy of osseous and soft tissue tumors. In the management of osteoid-osteoma, RFA is a well established treatment option. Basic principles, indications, complications and results of RFA will be presented. A careful evaluation of indications for RFA in osseous or soft tissue neoplasms is mandatory. In patients who are neither candidates for surgical tumor resection nor respond to chemotherapy, there is a need for alternative treatment options. In these preselected patients a substantial improvement in quality of life with low associated morbidity can be provided by RFA. In malignancies of bone and soft-tissue tumors, RFA is a palliative treatment option. Therefore, the results can not be compared to those of surgical resection or chemotherapy which essentially are employed with curative intention. Our own experiences as well as data published in the literature indicate that RFA is a helpful tool in preserving patient's quality of life. The high technical and clinical success together with a low complication rate makes RFA of osseous and soft tissue neoplasms a valuable supportive tool for patients not referable for surgery or systemic therapy.

Bone Neoplasms↗

PubMed2004

[MRI-assisted thermometry for regional hyperthermia and interstitial laser thermotherapy].

PURPOSE: To demonstrate the potential of quantitative MRI-assisted thermometry for the treatment of tumor patients with regional hyperthermia (RHT) and interstitial laser thermotherapy (ILTT). METHODS: Two patients and seven tissue samples were investigated using the T1-relaxation time and the chemical shift of the proton resonance frequency (PRF) as temperature sensitive MRI-parameters at 0.2 and 1.5 T. Thermotherapy was applied using either a dedicated MRI-hyperthermia hybrid system or a temperature controlled laser with 830 nm. RESULTS: Both patients were treated successfully showing clinical benefit. T1 and PRF are depending on the applied thermotherapy method and on the MR-system suitable for MRI-assisted thermometry. The clinical application based on phantom results is not necessarily adequate. CONCLUSION: Clinical application and phantom experiments of RHT and ILTT show the potential of MRI-assisted thermometry for further improvement of both minimal invasive thermotherapy methods. Further investigations concerning optimization of the MRI-techniques, the influence of perfusion or the determination of threshold values are necessary.

Adult↗

PubMed2004

[Cardiovascular whole body MRI with parallel imaging].

PURPOSE: To create a whole-body cardiovascular MRI protocol with parallel imaging (iPAT). MATERIAL AND METHODS: Twenty two persons participated in the whole body scan. Due to iPAT high resolution imaging of the heart could be performed. 3D contrast enhanced MR angiography (3D-CE-MRA) took only 62 s to cover the whole body at a spatial resolution of less than 1.4x1.0x1.5mm(3). Scan time for HASTE lung imaging could be reduced by the factor of 2 while maintaining the signal to noise ratio (SNR). Image quality was rated by 2 radiologists blinded to each other. RESULTS: Mean scan time was 104 min on the standard system and less than 80 min on the new system. 75% of all MRA segments were rated good in terms of vessel conspicuity, more than 80% had no venous overlay. One case of distal occlusion of the anterior tibial artery and two cases of myocardial infarction were detected. CONCLUSION: Parallel imaging offers the possibility of fast whole body imaging. A combination of morphologic and functional imaging can be performed within less than 80 min.

Adult↗

PubMed2004

[Comparison of high resolution whole-body MRI using parallel imaging and PET-CT. First experiences with a 32-channel MRI system].

PURPOSE: To compare the accuracy in the detection and staging of various malignant tumors with high resolution whole-body MRI using parallel imaging with whole-body dual-modality PET-CT. PATIENTS AND METHODS: Preliminary results of an interim analysis from a prospective, blinded study are presented, in which 20 patients (mean age 59 years, range 27-77 years) with different oncological diseases underwent whole-body dual modality FDG-PET-CT screening for tumor search or staging in case of confirmed or suspected metastatic disease. All patients also underwent whole-body MRI imaging with the use of parallel imaging (iPAT). High-resolution coronal T1w- and STIR-sequences of 5 body levels with 512 x 512 matrix, axial fast T2w imaging of lung and abdomen (HASTE), contrast-enhanced dynamic and static T1w-sequences of liver, brain, abdomen, and pelvis were performed. Using a 32-channel whole-body MRI scanner (Magnetom Avanto, Siemens Medical Solutions) with a total field of view of 205 cm and free table movement, all patients could be covered from head to toe within one examination. With this technique, high spatial resolution and acceptable scanning times could be obtained. Two experienced radiologists read the MRI-scans, one radiologist and one nuclear scientist read PET-CT scans, each in consensus in a clinical setting. Delineation of the primary tumor (T-stage) or recurrent tumor, pathologic lymph node involvement, as well as degree and localization of metastatic disease, was assessed using PET-CT as standard of reference. RESULTS: Metastases from gastrointestinal tumor (25%) and breast cancer (25%), genitourinary tumor (15%) and malignant melanoma (15%) were detected. In 4/20 patients the primary tumor was identified, 2/20 patients showed recurrent tumor. Of 140 malignant lesions detected by PET-CT, 124 lesions were detected with MRI, resulting in a sensitivity of 89% at a specificity of 86%. In malignant lymph node detection, sensitivity of MRI was 83% and specificity 85%. CONCLUSION: Whole-body MRI is a promising technique in the detection of primary tumor and metastatic disease. Sensitivity in the assessment of lymph node metastases seems to be limited. With the use of parallel imaging (iPAT), dedicated high-resolution whole-body MRI is possible within acceptable scanning times.

Adult↗

PubMed2004

[Diagnostic evaluation of carotid artery stenoses with multislice CT angiography. Review of the literature and results of a pilot study].

BACKGROUND: The accurate evaluation of carotid artery stenoses is important for therapeutic decision making. Catheter digital subtraction angiography (DSA) still represents the gold standard, while the advent of multislice CT (MSCT) has led to improved temporal and spatial resolutions of CTA. MATERIAL AND METHODS: In a pilot study, we investigated 14 diseased vessels in 9 symptomatic patients (7m, 2f; mean age 60.7+/-10,9 years) comparing biplanar DSA with standardized 16-slice MS-CTA. The degree of stenosis was evaluated in a consensus reading following modified NASCET criteria. RESULTS: DSA demonstrated 4 occlusions, 5 high-grade stenoses (>70%) and 5 lower-grade stenoses (<70%). One dissecting, infrapetrous stenosis was not adequately quantified by CTA due to a close topographic relation to the skull base. In the carotid bifurcation (n=13), an excellent correlation was demonstrated between DSA and CTA with a correlation coefficient of 0.99. CONCLUSION: MS-CTA has a good diagnostic potential in the evaluation of carotid artery stenoses. Larger studies will need to demonstrate the relative diagnostic value for different subtypes of stenosis and for different reader experience levels.

Aged↗

PubMed2004

[The significance of MR angiography for the diagnosis of carotid stenoses].

Arteriosclerosis of the supra-aortic vessels is a known risk factor for cerebrovascular disease. Large multicenter studies like NASCET and ECST have proven the protective effects of the surgical treatment of severe (>70%) carotid artery stenoses. The exact detection and grading of stenoses of the carotid arteries is a prerequisite for a successful therapy. Besides the gold-standard examination, digital subtraction angiography (DSA), MR angiography (MRA) is being used increasingly. MRA allows a non-invasive, high-resolution depiction of the supra-aortic vessels without ionizing radiation in only 20 s. This article first illustrates the MRA-techniques, and the indications and limitations of MRA. Next, the diagnostic accuracy of MRA is compared to DSA and ultrasound. The clinical value of MRA for the detection of stenoses of the carotid arteries is discussed on the basis of clinical examples.

Angiography, Digital Subtraction↗

PubMed2004

[Whole-body MRI and PET/CT in tumor diagnosis].

Tumor staging according to the TNM-system influences prognosis and therapeutical options of patients with a malignant disease. It is the challenge of diagnostic imaging to depict the exact localization of the primary tumor and to detect or rule out lymph node involvement or distant metastases. In doing so, the complete body anatomy should be covered with a modality that offers high sensitivity and specificity. As these requirements could not or only partially be achieved by previous ordinary procedures, the use of multiple different modalities became necessary. Last but not least, in consideration of the costs it would be preferable to replace this cascade of different modalities by a "whole body examination", preconditioned that the same accuracy is achieved.With PET/CT and whole-body MRI, two newly available promising methods for a systemic tumor staging have been developed. First experiences indicate PET/CT as a method of first choice. With the introduction of new whole-body MRI scanners using parallel imaging technique (iPAT) and free table movement, MRI plays a more and more important role in whole body tumor staging.

Adult↗