Forty-one patients demonstrating clinical symptoms for cerebral infarction were investigated by magnetic resonance imaging with diffusion-weighted echo-planar imaging (DWI) and T2-weighted imaging (T2WI). In 8 patients only DWI showed the cerebral lesions clearly. One patient with positive DWI and T2WI suffered from HSV encephalitis. DWI is superior to T2WI in assessment of small cortical infarcts and cerebral infarction in patients with preexisting vascular lesions. DWI is not specific, so other causes like cerebral hematoma and encephalitis have to be considered.
Investigations were carried out on a novel type of CT scanner, the Elscint CT-Twin, for comparison and optimization of the patient dose caused by standard and spiral CT of the head. For selected CT parameters, organ doses of the Alderson head phantom were measured with thermoluminescent dosemeters. Organ doses were also calculated using the normalized computed tomography dose index (CTDIn) combined with organ dose conversion factors. Then effective doses were deduced. For standard and spiral head CT examinations brain, red bone marrow and bone surface receive the main contributions to effective dose. This amounts to 0.9 and 0.8 mSv for routine standard and spiral CT, respectively, if the combination "dual-slice" mode, 250 mAs per rotation, 5 mm nominal slice width and a packing factor of 1.0, is applied. In clinical practice, for spiral CT head examinations the effective dose has been reduced to 0.7 mSv while guaranteeing adequate image quality, as assessed by determination of low and high contrast resolution. The effective dose values obtained are in the lower part of the range of values published in the literature. The dose determinations showed that, from the aspect of radiation protection of the patient, CT examinations with nominal slice widths between 0.5 and 1 mm as well as packing factors greater than 1.0 should be restricted to really necessary cases.
Zusamrnenfassung. Ziel der Arbeit war es, eine kernspintomographische Methode zu entwickeln, um den regionalen zerebralen BlutfluB (rCBF) in rol/100 g Hirngewebe/ min, das regionale zerebrale Blutvolumen (rCBV) in ml/100 g Hirngewebe und die ,,mean transit time" (MTT) in Sekunden aus den Daten einer dynamischen MR-Serie quantitativ zu berechnen und in Parameterbildern darzustellen. W~hrend einer Bolusinjektion von 0,1 mmol Gd-DTPA/kg KG wurde eine Serie transversaler T2*-gewichteter Bilddaten aufgenommen. Eine spezielle Software wurde entwickelt, um die relativen Kontrastmittelkonzentrationen zu berechnen und eine synthetische Kurve fª jedes Voxel an den Kontrastmittelverlauf anzupassen. Aus den Fitparametern liegen sich rCBV, rCBF und MTT ableiten und in Parameterbildern darstellen. Die berechneten rCBV-und rCBF-Werte von fª gesunden Probanden lagen im Bereich der Ergebnisse von PET-Untersuchungen. Bei neun Patienten mit zerebrovaskul~irer Erkrankung korrelierten die Perfusionsparameter mit Befunden von SPECT-und Xenon-CT-Untersuchungen. Diese Technik kann zur quantitativen Messung und Darstellung der Hirnperfusion eingesetzt werden. Sie ergibt fª Prognose und Therapie zus~tzliche Informationen bei Patienten mit zerebrovaskul~trer Erkrankung.
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