Biomedical subjects

U Mödder

Publications and source records attributed to U Mödder.

242 records · Page 14Linked to original sources

PubMedDate not supplied

MRI-guided laser-induced interstitial thermotherapy of cerebral neoplasms.

OBJECTIVE: Laser-induced interstitial thermotherapy (LITT) using a neodymium:yttrium aluminum garnet (Nd: YAG) laser is a new therapeutic approach in the treatment of brain tumors. The purpose of our study was to determine the value of MRI in monitoring LITT. MATERIALS AND METHODS: Eight patients with intracerebral tumors were treated with LITT. The light guide was inserted via an applicator sheath that was implanted stereotaxically with CT guidance. The laser irradiation was performed within the MR unit and monitored by repetitive measurements of a T1-weighted 2D-FLASH sequence. RESULTS: During therapy in all patients, typical changes of signal intensity were seen. A gradually increasing central zone of high signal intensity was surrounded by an increasing peripheral area of reduced signal intensity. The diameter of an enhancing rim at the outer border of the peripheral area after Gd-DTPA was considered as the total lesion size. The lesion size as determined on 2D-FLASH scans during LITT accounted for 88-100% (mean 93.5%) of total lesion size on T1-weighted images after Gd-DTPA acquired immediately after therapy. On T2-weighted images the signal intensities of the two zones were vice versa. Follow-up studies showed a decrease of total lesion size (15-87%). CONCLUSION: Our results demonstrate that MRI is feasible and effective in monitoring LITT. However, the role of LITT in the therapeutic workup of brain tumors still has to be defined in future clinical studies.

Adult↗

PubMedDate not supplied

Quantification of carotid blood flow velocity using MR phase mapping.

OBJECTIVE: The purpose of this study was to determine the feasibility of a two-dimensional phase-sensitive MR technique [phase mapping (PM)] for the quantification of carotid blood flow velocity (CBFV) and pulsatility in normal subjects and patients with extracranial carotid disease. MATERIALS AND METHODS: Using PM, we measured the systolic peak, minimum diastolic, and mean CBFV and the pulsatility index in both common carotid arteries (CCAs) of 22 normal subjects and 32 patients. In addition, the CBFV was quantified in the internal carotid arteries (ICAs) of 25 patients. These data were compared with independent measurements based on pulsed-wave Doppler ultrasonography. RESULTS: Correlations between PM and pulsed-wave Doppler were strong for systolic peak CBFV in both the CCA (r = 0.91) and the ICA (r > or = 0.82). Slightly lower correlations were obtained for mean CBFV (r > or = 0.79) and minimum diastolic CBFV (r > or = 0.75), both measured in the CCA. Velocity waveform comparison revealed high between-method correlations for the CCA (r = 0.90 for normals; r > or = 0.88 for patients) and slightly lower correlations for the ICA (r > or = 0.75). Agreement was lower (r = 0.63) for measurements in the ICA distal to high grade stenosis. CONCLUSION: Phase mapping compared well with Doppler ultrasonography in quantifying CBFV and pulsatility in patients with extracranial carotid artery disease. Except for poststenotic measurements in high grade obstructive lesions, PM is capable of providing quantitative hemodynamic information on the severity of ICA stenosis.

Adult↗

PubMedDate not supplied

MRI of the brain in Wilson disease: T2 signal loss under therapy.

Repeat examinations in a de novo patient with Wilson disease revealed an expansion of decreased signal intensities in the basal ganglia on T2-weighted imaging after initiation of copper trapping therapy. Since marked clinical improvement was associated with continued urinary copper excretion, iron depositioning in exchange for copper might explain these findings.

Adult↗

PubMedDate not supplied

Factors influencing flow-induced signal loss in MR angiography: an in vitro study.

OBJECTIVE: Signal loss due to poststenotic turbulence is one remaining limitation in the clinical use of MRA. The objective of this study was to determine the factors influencing poststenotic signal loss (PSL) in a stenotic tube system. MATERIALS AND METHODS: With use of a two-dimensional gradient echo sequence (FLASH), the influence of (a) the degree of stenosis (50, 75, and 91% cross-sectional area reduction), (b) flow velocity (12, 47, 71, and 94 cm/s), (c) TE (3, 6, 13, and 20 ms), and (d) flip angle (5, 10, 20, ... , 90 degrees) on the length of PSL was measured in a nonpulsatile stenotic tube system. To quantify the effect of first-order gradient motion refocusing (GMR), the signal intensity ratio from flow-compensated and -uncompensated images was calculated. For statistical analysis, multiple regression analysis and unpaired Student t test were used. RESULTS: In the flow model used, the length of PSL increased significantly with the degree of stenosis (beta ST' = 0.483 mm/%, beta ST" = 0.447 mm/%, p < 0.0001), flow velocity (beta v' = 0.297 s, beta v" = 0.213 s, p < 0.0001), and TE (beta TE = 1.88 mm/ms, p < 0.0001), respectively, whereas no correlation emerged for varying flip angles (beta alpha = 0.0214, p = 0.29). First-order GMR reduced significantly PSL in through-plane measurements (p < 0.0001). Maximal signal-enhancing effects of first-order GMR were observed 1-3 cm distal to the stenosis. CONCLUSION: Flow model parameters (i.e., degree of stenosis, flow velocity) markedly influenced the length of PSL that could be compensate for by use orf shortened TEs and first-order GMR. Varying flip angles had no significant influence on PSL.

Acrylic Resins↗

PubMedDate not supplied

Cerebral blood volume maps with dynamic contrast-enhanced T1-weighted FLASH imaging: normal values and preliminary clinical results.

PURPOSE: In this article we investigate the application of a method that uses the relaxation effect of bolus-like injected Gd-DTPA to quantify regional cerebral blood volume (rCBV). The aim of the study was to determine if the method provides correct rCBV values in healthy subjects as well as to obtain additional diagnostic information for patients with a glioma or stroke. METHOD: Twenty healthy subjects, 12 patients with brain infarctions, and 18 patients with gliomas were examined. A series of 64 sequential images of one slice was recorded during bolus transit with a FLASH sequence. The measured signal intensity-time curves were converted pixel-wise to concentration-time curves from which the rCBV images were calculated applying the indicator dilution method. RESULTS: An average value for gray and white matter of 4.4 +/- 1.6 vol% was obtained for the group of healthy subjects. The grading of the tumors could be classified according to the differences of their corresponding rCBV values. Fifty percent of the infarct patients had to be excluded from the analysis in the acute phase due to mispositioning of the slice and data degradation by gross motion artifact. Different rCBV values were found for areas that develop later into gliotic scars or cystic necrosis. CONCLUSION: The proposed method is easy to apply in clinical routine MR investigations and provides valuable information for noninvasive, preoperative assessment of tumor grading. It can also provide additional criteria for estimating the histological outcome and with it the degree of ischemia in stroke patients.

Adolescent↗

PubMedDate not supplied

Comparison of cerebral blood volume measurements using the T1 and T2* methods in normal human brains and brain tumors.

PURPOSE: Regional cerebral blood volume (rCBV) can be determined after bolus injection of a contrast agent by utilizing the susceptibility effect (T2* method) or the relaxation effect (T1 method). The aim of this study was to apply both methods in groups of normal subjects and tumor patients and to compare the results. METHOD: CBVs in different brain areas were determined from groups of 18 normal subjects and 21 patients with different histologically classified tumors. Measurements were performed using GE sequences on a 1.5 T scanner without echo planar imaging capability. As a measure of quality of a single examination, the temporal behavior of the contrast agent bolus was characterized using parameters such as rise time, peak value, fall time, and full width at half-maximum of the concentration-time curves. RESULTS: The quality of the T2* measurements was inferior to that obtained with the T1 method. A mean CBV value of 4.1 + 1.1 vol% averaged over the entire brain area was found in the normal collective with the T1 method. The value obtained with the T2* method was 2.6 +/- 1.1 vol%. Similar underestimations of the CBV values were also found using the T2* method when evaluating regions of interest in tumor patients. CONCLUSION: Both methods are able to determine rCBV in routine clinical studies. If the goal is to obtain quick, qualitative multislice information, the T2* method is adequate. For quantitative evaluations, however, the T1 method should be preferred.

Adolescent↗

PubMedDate not supplied

Azygos continuation syndrome with aneurysm of the azygos vein: CT and MR appearances.

We present a case of azygos vein continuation with aneurysm of the azygos vein simulating a tumor in the right upper mediastinum. The dynamic CT examination initially showed a structure of malignant appearance during the early arterial phase. Further dynamic CT revealed marked enhancement of the mass during the late venous phase, suggesting a vascular structure. Confirmation of diagnosis was made by MRI using a fast gradient echo imaging technique in cine mode, showing turbulent flow in the azygos aneurysm, and contrast-enhanced MR angiography, demonstrating a dilated azygos vein. Dynamic CT has a potential pitfall in the diagnosis of vascular structures.

Aneurysm↗

PubMedDate not supplied

Age-dependent changes in magnetization transfer contrast of white matter in the pediatric brain.

BACKGROUND AND PURPOSE: It is unknown to what extent magnetization transfer contrast (MTC) in white matter of the brain changes during myelination. The goal of this study was to measure the age-dependent changes of MTC in different regions of the pediatric brain and to evaluate their relation to T2 relaxation times. METHODS: Seventy children aged 1 week to 80 months without evidence of organic brain disease underwent MR imaging of the brain. A double-echo spin-echo (SE) sequence and an SE sequence with and without an off-resonance pulse were performed in the axial orientation. Using paired images, we calculated MTC ratios in 13 predefined regions of the brain and compared them with the T2 relaxation times measured in the same areas. Regression analysis was performed for both parameters to evaluate age dependency. RESULTS: MTC in white matter increased during myelination from a range of 13% to 19% to a range of 34% to 37%. At the same time, T2 relaxation times decreased from a range of 115 to 160 milliseconds to a range of 60 to 70 milliseconds after myelination. For both MTC and T2 relaxation times, age dependency could be expressed by a monoexponential function. CONCLUSION: A strong positive correlation exists between MTC ratios and the degree of myelination in the pediatric brain, and an inverse correlation exists between MTC and T2 relaxation times. Fast proton relaxation within macromolecules in the myelinated white matter and subsequent MT may be the most important reason for the decreasing T2 relaxation time of white matter during brain myelination.

Aging↗