Thomas Hackländer

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.

1H T1 and T2 measurements of the MR imaging contrast agents Gd-DTPA and Gd-DTPA BMA at 1.5T

Abstract We report in vitro T1 and T2 relaxation studies for the open-chain complexes Gd-DTPA and Gd-DTPA BMA. Measurements were performed on phantoms containing aqueous and plasma solutions of different concentrations by MR imaging in a 1.5T superconducting whole-body scanner. Longitudinal relaxation times T1 were evaluated from serial turbo-FLASH experiments for concentrations less than 1 mM, whereas for larger concentrations the values were obtained from a standard inversion recovery (IR) sequence. Transverse relaxation times T2 were determined using multi-echo spin-echo MRI protocols. The T1 and T2 relaxivities of the nonionic Gd-DTPA BMA are similar to those of the Gd-DTPA. The temperature dependencies of the relaxivities were determined over a temperature interval ranging from 21 to 50 °C and were found to be slightly different for the two contrast agents. In the case of Gd-DTPA BMA a larger deviation of the expected temperature behavior of the relaxivities was observed as compared with Gd-DTPA. Deviations from a strictly linear dependence of relaxation times on temperature were found at lower concentrations in aqueous solutions. In plasma solutions a high T1/T2 ratio was observed for low concentrations, which decreased monotonically with increasing concentrations.

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.

Individual Integration of Positron Emission Tomography and High-Resolution Magnetic Resonance Imaging

We have developed, validated, and employed a technique of retrospective spatial alignment and integrated display of positron emission tomographic (PET) and high-resolution magnetic resonance (MR) brain images. The method was designed to improve the anatomical evaluation of functional images obtained from single subjects. In the first computational step, alignment of PET and MR data sets is achieved by iteratively matching in three orthogonal views the outermost scalp contours derived from front-to-back projections of each data set. This procedure avoids true three-dimensional modeling, runs without user interaction, and tolerates missing parts of the head circumference in the image volume, as usually the case with PET. Thereafter, high-resolution MR sections corresponding to the PET slices are reconstructed from the spatially transformed MR data. In a phantom study of this method, PET/MR alignment of the phantoms surface was accurate with average residual misfits of 2.17 to 2.32 mm as determined in three orthogonal planes. In-plane alignment of the phantoms insertion holes was accurate with an average residual misfit of 2.30 mm. In vivo application in six subjects allowed the individual anatomical localization of regional CBF (rCBF) responses obtained during unilateral manual exploration. In each subject, the maxima of the rCBF activations in the hand area were precisely allocated to gray matter in the anterior or posterior wall of the central sulcus. The configuration of the rCBF responses closely followed the gyral structures. The technique provided a better topographical understanding of rCBF changes in subtraction images of PET activation studies. It opens the perspective for studies of structural–functional relationships in individual subjects.

Evaluation of renovascular hypertension: comparison of functional MRI and contrast-enhanced MRA with a routinely performed renal scintigraphy and DSA.

Objective: The main objective of this study was to evaluate a clinically suspected renovascular hypertension (RVH) by means of MRI. It was to find out if functional MRI (fMRI) is able to provide adequate results with regard to MAG3 captopril scintigraphy and if contrast-enhanced MR angiography (MRA) is able to provide adequate results in the stenosis grading compared with the nonselective digital subtraction angiography (DSA). Methods: This open, monocentric, prospective, phase 3 study included patients with a clinically suspected RVH. For fMRI a dynamic TurboFLASH sequence and for MRA a single-shot breath-hold flash 3D sequence was performed. Gadodiamide was injected as contrast medium. Results: Sixty patients were included in the study. The correlation between fMRI and scintigraphy had an accuracy, a sensitivity, and a specificity of 69%, 5%, and 92%, respectively, and correlations between MRA and DSA of 95%, 92%, and 96%. Conclusion: The noninvasive MRA can replace DSA in the diagnosis of renal artery stenosis. However, fMRI can not replace renal scintigraphy.

Agreement of multislice CT angiography and MR angiography in assessing the degree of carotid artery stenosis in consideration of different methods of postprocessing.

Objective: We investigated the agreement of multislice computed tomography angiography (CTA) and magnetic resonance angiography (MRA) in the quantitative measurement of carotid artery stenosis. The dependency of the agreement of the chosen postprocessing procedures was also investigated. Methods: Fifty consecutive symptomatic patients were included in this study. In all patients, a CTA was performed with a 16-slice CT scanner. Within 30 days, the extracranial vessels were examined using a combined time-of-flight and contrast-enhanced MRA. The CT data sets were used to calculate the degree of stenosis according to the North American Symptomatic Carotid Endarterectomy Trial, European Carotid Surgery Trial, and Common Carotid methods by means of the 1-mm thick, transverse raw data (RD), a sagittal maximum-intensity projection reconstruction, and sagittal multiplanar reconstruction. In addition, a semiautomated analysis was done using a specialized postprocessing software. For all combinations of postprocessing procedures and methods of calculating the degree of stenosis, the correlation coefficient and the agreement based on Bland/Altman plots were calculated. Results: Eleven of the 100 primarily included carotid arteries could not be evaluated. The correlation coefficients for all combinations were comparable and lied in the interval between 0.932 and 0.787. The best correlation was found for the combination of RD/sagittal multiplanar reconstruction and ECST method. The evaluation of the agreement gave a systematic overestimation of CTA between 1.9% and 10.7% with a 95% confidence interval between ±26.7% and ±43.3%. With the semiautomated postprocessing software, additional 33 vessels could not be evaluated. The agreement of the calculated degrees of stenoses was worse than that of the planar procedures. Conclusions: CTA and MRA had a feasible agreement in measuring the degree of stenosis of the carotid arteries. The best result could be obtained for the evaluation of the RD and the NASCET method. In this case one has to take into account a systematic overestimation of CTA of 1.9%. The combination with an additional reconstructive postprocessing procedure did not improve the result but might be useful for the radiologist to identify the location of the closest narrowing.

Effect of partial volume correction on muscarinic cholinergic receptor imaging with single-photon emission tomography in patients with temporal lobe epilepsy

Animal experiments and preliminary results in humans have indicated alterations of hippocampal muscarinic acetylcholine receptors (mAChR) in temporal lobe epilepsy. Patients with temporal lobe epilepsy often present with a reduction in hippocampal volume. The aim of this study was to investigate the influence of hippocampal atrophy on the quantification of mAChR with single photon emission tomography (SPET) in patients with temporal lobe epilepsy. Cerebral uptake of the muscarinic cholinergic antagonist [123I]4-iododexetimide (IDex) was investigated by SPET in patients suffering from temporal lobe epilepsy of unilateral (n=6) or predominantly unilateral (n=1) onset. Regions of interest were drawn on co-registered magnetic resonance images. Hippocampal volume was determined in these regions and was used to correct the SPET results for partial volume effects. A ratio of hippocampal IDex binding on the affected side to that on the unaffected side was used to detect changes in muscarinic cholinergic receptor density. Before partial volume correction a decrease in hippocampal IDex binding on the focus side was found in each patient. After partial volume no convincing differences remained. Our results indicate that the reduction in hippocampal IDex binding in patients with epilepsy is due to a decrease in hippocampal volume rather than to a decrease in receptor concentration.

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 ≥ 0.82). Slightly lower correlations were obtained for mean CBFV (r ≥ 0.79) and minimum diastolic CBFV (r ≥ 0.75), both measured in the CCA. Velocity waveform comparison revealed high between-method correlations for the CCA (r = 0.90 for normals; r ≥ 0.88 for patients) and slightly lower correlations for the ICA (r ≥ 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.

An efficient and robust PC program to calculate MR based regional cerebral blood volume maps

In addition to morphological and anatomical information, functional information is increasingly used in clinical routine to assess pathological alterations of the brain. In addition to nuclear-medical methods there is a growing interest in using magnetic resonance imaging (MRI) to investigate tissue perfusion of the brain. The method employed is based on the indicator-dilution method after bolus injection of a contrast agent. In this paper we present the implementation of an efficient algorithm to calculate quantitatively the regional cerebral blood volume (rCBV). Computation requires about 1 min on a Macintosh Quadra 660AV. The results are represented as parameter images that allow global overall visual inspection as well as quantitative local evaluation by means of user-defined regions of interest.

Ein System zur funktionellen Perfusionsuntersuchung der Niere bei gleichzeitiger Unterdrückung der Atembewegung des Organs

Fur viele weitverbreitete Erkrankungen, wie z.B. den krankhaft erhohten Blutdruck, sind Funktionseinschrankungen der Nieren verantwortlich. Als Diagnosemethode ohne Strahlenexposition findet die Kernspintomographie (MRT) in der Medizin vermehrt Anwendung. Durch Auswertung der Passage eines Kontrastmittels (KM) durch das Organ fur verschiedene Regionen der Niere (Rinde, Mark, Gesamtorgan) werden Signalintensitats-Zeitkurven ermittelt. Die Nierenfunktion ergibt sich aus speziellen Parametern dieser Kurven. Eine computerunterstutzte Auswertung hat zwei Hauptprobleme zu bewaltigen. Einmal mussen Verschiebungen der Nieren wahrend der Aufnahme, verursacht durch Atmung des Patienten, korrigiert werden. Zum anderen wird eine prazise Gewebedifferenzierung fur Nierenmark und -rinde durch die spezielle Form der Nieren und die Bildqualitat der Aufnahme erschwert. Das vorgestellte Systems lost beide Probleme und verkurzt die Bearbeitungszeit bis zur Diagnosestellung erheblich.