Timo Kurki

MR classification of brain gliomas: Value of magnetization transfer and conventional imaging

We compared quantitative analysis of conventional MR and magnetization transfer (MT) images with visual morphologic assessment of standard images in the classification of gliomas. Thirty-two patients with gliomas were imaged preoperatively. Relative signal intensities on T2- and T1-weighted images, Gd-enhancement, signal heterogeneity on T2-weighted and Gd-enhanced T1-weighted images and MT ratios were measured. In 16 astrocytomas, the MT ratios were correlated with the volume fraction of tumor cell nuclei in histological sections. Among the conventional sequences T2-weighted images were most accurate for quantitative classification; signal heterogeneity was more accurate than relative signal intensity. MT ratios were superior to quantitative analysis of conventional images and equal to visual morphologic evaluation in discriminating between low-grade and high-grade gliomas and correlated with the volume fraction of nuclei in the tumor tissue (r = 0.71, p < .01). The results indicate that quantitative analysis is generally of minor value in the grading of gliomas. In spite of sensitivity to tissue changes associated with malignancy MT imaging cannot significantly improve MR classification of gliomas.

Magnetic resonance imaging of the brain used to detect early post-partum activation of multiple sclerosis

Post‐partum relapses are a frequent phenomenon in multiple sclerosis (MS). The purpose of this study was to evaluate the timing and extent of new or growing T2‐lesions after delivery in a cohort of Finnish MS patients. In addition to serial magnetic resonance imaging (MRI), the patients were followed up clinically with determination of relapse rate and expanded disability status scale. The annualized relapse rate was decreased during the last trimester of pregnancy [mean 0.14, standard deviation (SD) 0.14] when compared with the time before pregnancy (mean 0.64, SD 0.14; P = 0.04) and to time post‐partum (mean 1.50, SD 0.45; P = 0.0002). New or enlarging lesions were detected in the post‐partum images in 14 of 28 patients. Gadolinium‐enhancing lesions in post‐partum MRI were present in eight of 13 patients. There was a significant increase in the number of T2‐lesions (P = 0.0009), in the total volume of MS‐lesions measured from fluid‐attenuated inversion recovery images (P = 0.0126) and in the number of diffusion weighted imaging hyperintense lesions (P = 0.0098) in the post‐partum images. The clinical results support the earlier findings of decreased disease activity in late pregnancy. The clinical and MRI findings indicate that post‐partum activation is an early and common phenomenon amongst mothers with MS.

MR imaging of head trauma: visibility of contusions and other intraparenchymal injuries in early and late stage.

The aim of this study was to investigate the visibility of traumatic brain lesions on conventional magnetic resonance images (MRI) in early and late phase. Thirty-six patients were studied 1 week and 1 year after a traumatic brain injury. A similar MRI technique was used in both studies; T2-weighted fast or turbo spin echo images, fluid attenuated inversion recovery (FLAIR) images and T1-weighted images were used for analysis. The number and extent of contusions and semi-quantitative score of other traumatic intraparenchymal lesions were compared in the early and late phase. Contusions were seen in 18 patients both in acute and 1 year MRI; the number and extent of visible contusions was significantly decreased at 1 year. Other traumatic intraparenchymal lesions were detected in 12 patients in early MRI and in 10 patients in late MRI. The number of visible lesions and the semi-quantitative scores were significantly lower at 1 year. There is a significant decrease in the visibility of both cortical contusions and other intraparenchymal injuries in late MRI studies compared with studies in acute stage using conventional imaging techniques. Thus, early phase MRI is essential for the detection of brain injury at least using conventional imaging techniques.

Tissue characterisation of intracranial tumours: the value of magnetisation transfer and conventional MRI

We performed MRI on 85 patients with intracranial tumours to evaluate quantitative analysis in tumour characterisation. Signal intensities were measured on standard T2-and T1-weighted images, Gd-enhanced T1-weighted images and magnetisation transfer (MT) images. Statistically significant differences between tumour types were observed, but overlapping reduces their value. T2-weighted imaging was superior to T1-weighted imaging for tumour characterisation. Quantification of Gd enhancement was useful in the diagnosis of pituitary adenomas and haemangioblastomas, but of minor importance in other tumours, because of large nonspecific variation. The contribution of MT contrast to tumour characterisation resembled that of T2 contrast. However, MT imaging was superior to other sequences in the classification of intra-axial tumours. Low-grade astrocytomas, haemangioblastomas and craniopharyngiomas could be differentiated from other tumours on the basis of MT contrast. Reliable discrimination between meningiomas, high-grade astrocytomas and metastases was not possible by any of the methods.

MRI findings and Axis I and II psychiatric disorders after traumatic brain injury: a 30-year retrospective follow-up study.

We studied the association between psychiatric disorders and the presence and location of traumatic lesions on magnetic resonance imaging (MRI) in 58 patients, on average, 30 years after traumatic brain injury. Axis I psychiatric disorders that had begun after the injury were assessed with the Schedules for Clinical Assessment in Neuropsychiatry (version 2.1), and Axis II disorders with the Structured Clinical Interview for DSM-III-R Personality Disorders. A 1.5-Tesla MRI scanner was used. One-third of the subjects had traumatic lesions visible on MRI. Only three psychiatric disorders, that is, delusional disorder, dementia, and the disinhibited type of organic personality syndrome, were significantly more common in subjects with contusions. Concerning the location of contusions, organic personality syndrome and its disinhibited subtype were associated with frontal lesions, and major depression was, surprisingly, inversely associated with temporal lesions. These results, which should be interpreted with caution due to the limited size of the study group, suggest that the majority of psychiatric disorders after traumatic brain injury are not closely related to the specific location or even the presence of contusions detectable with post-acute MRI.

Spin-lattice relaxation and magnetization transfer in intracranial tumors in vivo: Effects of Gd-DTPA on relaxation parameters

Spin-lattice relaxation time T1 and relaxation parameters in magnetization transfer (MT) imaging were measured in 11 intracranial tumors before and after injection of Gd-DTPA at 0.1 T by using the inversion recovery method and the saturation transfer technique, respectively. Preinjection T1 relaxation times of the tumors were longer than those of white matter, but after Gd-enhancement the relaxation times of most tumors were in the same range as those of white matter. Gd-DTPA shortened the apparent relaxation time in the presence of off-resonance saturation pulse (T1a) due to marked shortening of the relaxation time of mobile water (T1w). Gd-DTPA decreased the magnetization transfer contrast (MTC) but did not influence on the magnetization transfer rate (Rwm). The parameters MTC and Rwm differed clearly between Gd-enhanced tumors and normal brain, whereas the relaxation time T1a was in many Gd-enhanced tumors in the same range as in normal brain.

Reproducibility of Tract-based and Region-of-Interest DTI Analysis of Long Association Tracts.

PurposeReproducibility of two different methods for quantifying fiber tracts by using a diffusion tensor imaging (DTI) sequence suitable for clinical magnetic resonance imaging (MRI) protocols was evaluated.MethodsDTI of 15 subjects was used to analyze intra-rater and inter-rater reproducibility. Another 10 subjects underwent MRI twice for assessment of between-scan reliability. Ten long association tracts were defined by fiber tracking using inclusion and exclusion regions of interest (ROIs). Whole-tract analysis and tractography-based core analysis were performed, and the effect of fractional anisotropy (FA 0.15/0.30) and turning angle threshold (27°/60°) on reproducibility was evaluated. Additionally, ROI measurements were performed in the core of the tracts.ResultsFor the tract-based methods, intra-rater and inter-rater reliabilities of FA and mean diffusivity (MD) measurements were excellent. Between-scan reproducibility was good or excellent in 127 of 130 of the measurements. There was no systematic difference in the reproducibility of the FA, MD, and volume measurements depending on the FA or turning angle threshold. For the cross-sectional ROI measurements, reliability showed large variation from poor to excellent depending on the tract.ConclusionsCompared with the commonly used cross-sectional core ROI method, the tract-based analyses seem to be a more robust way to identify and measure white matter tracts of interest, and provide a novel reproducible tool to perform core analysis.

T1 in subacute and chronic brain infarctions. Time-dependent development.

RATIONALE AND OBJECTIVES Time-dependent behavior of T1 in brain infarcts and in brain tissue of the contralateral hemisphere was studied in the subacute and early chronic stages of stroke. METHODS T1 was measured from magnetic resonance images (MRIs) of 29 patients as a function of infarct location and age. Another group of 11 patients was studied with consecutive MRI studies during the first 5 weeks after the onset of infarct, and the distribution of T1 in the infarctions was analyzed from T1 maps using a histographic method. RESULTS During the first 2 months after a stroke, T1 was longer in the infarcted gray matter than in the infarcted white matter (P = .002), and prolonged linearly in both. The histographic analysis showed a component arising from tissue breakdown products that could be identified for up to 5 weeks. A transient lengthening in T1 of the contralateral hemisphere, reaching a maximum at 3 weeks, also was observed. CONCLUSIONS These characteristics of recent infarctions differentiate them from older, gliotic lesions. The lengthening of T1 in the contralateral hemisphere may reflect remote flow and metabolic effects of brain infarctions.

Apparent Diffusion Coefficient Histograms in the Follow-up of Relapsing-Remitting Multiple Sclerosis.

Diffusion-weighted (DW) magnetic resonance (MR) imaging in addition to conventional magnetic resonance MR images provide valuable information in multiple sclerosis (MS). Increased diffusivity measured with diffusion-weighted imaging (DWI) has been demonstrated in normal appearing brain tissue in MS. So far, longitudinal changes taking place in whole-brain histograms in patients with active relapsing-remitting MS have not been evaluated. The aim of this study was to evaluate how apparent diffusion coefficient (ADC) histograms are altered during the follow-up of active relapsing-remitting MS patients. Nine patients were studied twice by MRI with a three-month interval. All patients had active newly diagnosed MS with two to three relapses during the year preceding the first MRI, and interferon-beta treatment was initiated after obtaining the first image. ADC histograms were produced after removing extracranial tissues and cerebrospinal fluid from the images. Additionally, brain volume index (BVI) and lesion volume on FLAIR images were measured. Five patients had signs of disease activity in the follow-up MRI. In the four patients without signs of disease activity the change in ADC histogram parameters was less than 2%. In patients with disease activity both increase (one case) and decrease (four cases) in histogram parameters were detected. Changes in BVI or lesion volume did not significantly correlate with histogram changes. The number of new T2-lesions showed a positive correlation with mean (r=0.79, P=0.014) and upper quartile (r=0.77, P=0.021) value change. Alterations in disease activity lead to histogram changes; both shifts to lower values and shifts to higher values are possible. The histogram changes are mostly related to subtle inflammatory changes in normal appearing brain tissue during inflammatory activity and their resolution during less active inflammatory conditions.