MR imaging of the hippocampus: measurement of T2 with four dual-echo techniques

Performance of t1 and t2 mapping cardiovascular magnetic resonance to detect active myocarditis in patients with recent-onset heart failure

BACKGROUND

This study evaluated the performance of novel quantitative T1 and T2 mapping cardiovascular magnetic resonance (CMR) techniques to identify active myocarditis in patients with recent-onset heart failure.

METHODS AND RESULTS

Thirty-one consecutive patients with recent-onset heart failure, reduced left ventricular function and clinically suspected myocarditis underwent endomyocardial biopsy and CMR at 1.5 Tesla. The CMR protocol included standard Lake-Louise parameters as well as T1 mapping using a modified Look-Locker inversion recovery sequence and T2 mapping using a hybrid gradient and spin-echo sequence. Short-axis maps were generated using an OsiriX plug-in to calculate global myocardial T1, T2, and extracellular volume fraction. Active myocarditis was defined by ongoing inflammation on endomyocardial biopsy. Endomyocardial biopsy revealed active myocarditis in 16 (52%) of 31 patients. Neither clinical characteristics, standard Lake-Louise CMR parameters, global myocardial T1 nor extracellular volume fraction differed significantly between patients with and without active myocarditis. However, median global myocardial T2 was significantly higher in patients with active myocarditis (65 ms [Q1-Q3, 61-70 ms]) than in patients without active myocarditis (59 ms [Q1-Q3, 55-64 ms]; P<0.01). A cutoff value for global myocardial T2 of ≥60 ms provided a sensitivity, specificity, accuracy, negative and positive predictive value of 94% (70%-100%), 60% (32%-84%), 77% (60%-89%), 90% (56%-100%), and 71% (48%-89%) for active myocarditis, respectively.

CONCLUSIONS

T2 mapping seems to be superior when compared with standard CMR parameters, global myocardial T1, and extracellular volume fraction values for assessing the activity of myocarditis in patients with recent-onset heart failure and reduced left ventricular function.

Development of T2-relaxation values in regional brain sites during adolescence

Brain tissue changes accompany multiple neurodegenerative and developmental conditions in adolescents. Complex processes that occur in the developing brain with disease can be evaluated accurately only against normal aging processes. Normal developmental changes in different brain areas alter tissue water content, which can be assessed by magnetic resonance (MR) T2 relaxometry. We acquired proton-density (PD) and T2-weighted images from 31 subjects (mean age±S.D., 17.4±4.9 years; 18 male), using a 3.0-T MR imaging scanner. Voxel-by-voxel T2-relaxation values were calculated, and whole-brain T2-relaxation maps constructed and normalized to a common space template. We created a set of regions of interest (ROIs) over cortical gray and white matter, basal ganglia, amygdala, thalamic, hypothalamic, pontine and cerebellar sites, with sizes of ROIs varying from 12 to 243 mm(3); regional T2-relaxation values were determined from these ROIs and normalized T2-relaxation maps. Correlations between R2 (1/T2) values in these sites and age were assessed with Pearson's correlation procedures, and gender differences in regional T2-relaxation values were evaluated with independent-samples t tests. Several brain regions, but not all, showed principally positive correlations between R2 values and age; negative correlations emerged in the cerebellar peduncles. No significant differences in T2-relaxation values emerged between males and females for those areas, except for the mid pons and left occipital white matter; males showed higher T2-relaxation values over females. The findings indicate that T2-relaxation values vary with development between brain structures, and emphasize the need to correct for such age-related effects during any determination of potential changes from control values.

FLAIR signal and texture analysis for lateralizing mesial temporal lobe epilepsy

Standard magnetic resonance (MR) imaging analysis in several cases of mesial temporal lobe epilepsy (mTLE) either fail to show an identifiable hippocampal asymmetry or provide only subtle distinguishing features that remain inconclusive. A retrospective analysis of hippocampal fluid-attenuated inversion recovery (FLAIR) MR images was performed in cases of mTLE addressing, particularly, the mean and standard deviation of the signal and its texture. Preoperative T1-weighted and FLAIR MR images of 25 nonepileptic control subjects and 36 mTLE patients with Engel class Ia outcomes were analyzed. Patients requiring extraoperative electrocorticography (ECoG) with intracranial electrodes and thus judged to be more challenging were studied as a separate cohort. Hippocampi were manually segmented on T1-weighted images and their outlines were transposed onto FLAIR studies using an affine registration. Image intensity features including mean and standard deviation and wavelet-based texture features were determined for the hippocampal body. The right/left ratios of these features were used with a linear classifier to establish laterality. Whole hippocampal within-subject volume ratios were assessed for comparison. Mean and standard deviation of FLAIR signal intensities lateralized the site of epileptogenicity in 98% of all cases, whereas analysis of wavelet texture features and hippocampal volumetry each yielded correct lateralization in 94% and 83% of cases, respectively. Of patients requiring more intensive study with extraoperative ECoG, 17/18 were lateralized effectively by the combination of mean and standard deviation ratios despite a ratio of mean signal intensity near one in some. The analysis of mean and standard deviation of FLAIR signal intensities provides a highly sensitive method for lateralizing the epileptic focus in mTLE over that of volumetry or texture analysis of the hippocampal body.

Quantitative analysis of temporal lobe white matter T2 relaxation time in temporal lobe epilepsy

The objective of this study was to assess temporal lobe white matter (WM) quantitatively using T2 relaxometry in patients with pharmacologically intractable temporal lobe epilepsy (TLE). T2 relaxometry was performed using a dual-echo sequence with 23 contiguous oblique coronal slices in 56 consecutive TLE patients and in 30 healthy subjects. Averages of six slices were chosen to calculate T2 relaxation time in the temporal lobe WM (WM-T2) and the hippocampus (Hippo-T2). Twenty-seven patients had unilateral hippocampal atrophy (HA), and twenty-nine patients had normal hippocampal volumes (NV) on volumetric MRI. Mean WM-T2 was increased ipsilateral to the seizure focus in TLE patients with HA and those with NV (P < 0.001). Contralateral mean WM-T2 was increased in left and right TLE with HA (P < 0.001) and in right TLE with NV (P = 0.001). There was a positive correlation between WM-T2 and Hippo-T2. Individual analysis showed a prolongation of WM-T2 in about 70% of TLE patients with HA and NV. In half of the patients, WM-T2 increase was bilateral and symmetric. However, in 33% of patients with NV and bilateral symmetric increase in Hippo-T2, WM-T2 provided a correct lateralization of the seizure focus. Regardless of the pattern of T2 abnormalities, that is, bilateral symmetric or ipsilateral, the majority of patients with HA became seizure-free after surgery, while those with NV did not have a favorable outcome. In patients with NV, WM-T2 measurement may provide additional lateralizing information compared to Hippo-T2.

Magnetization transfer and T2 quantitation in normal appearing cortical gray matter and white matter adjacent to focal abnormality in patients with traumatic brain injury

Traumatic brain injury (TBI) is one of the commonest causes of morbidity and mortality in the developed countries with posttraumatic epilepsy and functional disability being its major sequelae. The purpose of this study was to test the hypothesis whether the normal appearing adjacent gray and white matter regions on T2 and T1 weighted magnetization transfer (MT) weighted images show any abnormality on quantitative imaging in patients with TBI. A total of 51 patients with TBI and 10 normal subjects were included in this study. There were significant differences in T2 and MT ratio values of T2 weighted and T1 weighted MT normal appearing gray matter regions adjacent to focal image abnormality compared to normal gray matter regions in the normal individuals as corresponding contralateral regions of the TBI patient's group (p < 0.05). However the adjoining normal appearing white matter quantitative values did not show any significant change compared to the corresponding contralateral normal white matter values. We conclude that quantitative T2 and MT ratio values provide additional abnormality in patients with TBI that is not discernable on conventional T2 weighted and T1 weighted MT imaging especially in gray matter. This additional information may be of value in overall management of these patients with TBI.

Multiparametric quantitation of the perilesional region in patients with healed or healing solitary cysticercus granuloma

The purpose of this study was to compute T2 values and magnetization transfer (MT) ratios in the perilesional region of healing and healed cysticercus granulomas to determine if there are T2 abnormalities not apparent on conventional T2-weighted imaging and to determine the relationship between seizure control and the quantitative measures. Sixty-three patients were studied. T2 values and MT ratios were computed for the perilesional region and were compared with measurements from the contralateral normal-appearing region. A significantly increased T2 value was found for the perilesional region compared to the corresponding contralateral region despite the absence of qualitative abnormality on conventional T2-weighted magnetic resonance imaging. For patients showing normal-appearing perilesional regions on MT imaging, there was no significant difference in T2 and MT ratios between the perilesional and the normal contralateral regions. There was a statistically significant inverse correlation between perilesional T2 values and MT ratios, suggesting each was associated with perilesional gliosis. The study illustrates that quantitative evaluation of MT ratios and T2 augments the qualitative visual assessment of the perilesional region in healing or healed cysticercus granulomas.

A fast FLAIR dual-echo technique for hippocampal T2 relaxometry: first experiences in patients with temporal lobe epilepsy

To evaluate the use of cerebrospinal fluid (CSF) signal nulling in MR T2 measurements of the hippocampus in normal control subjects and patients with temporal lobe epilepsy (TLE), dual-echo acquisitions covering the whole brain were used. T2 relaxation times were estimated in 12 standard Eurospin II MR test objects and in the hippocampi of 10 control subjects, using T2 maps constructed from conventional spin-echo (CSE), fast spin-echo (FSE), and fast FLAIR (FF) dual-echo sequences on a 1.5-T MR scanner. Hippocampal T2 values (HCT2) were measured on contiguous coronal 5-mm slices throughout the antero-posterior extent of each hippocampus in the 10 controls and 12 TLE patients, using both CSE and FF. Scan-rescan reproducibility in Eurospin II standard MR test objects was high for all sequences. There was a good correlation between T2 values from CSE, FF, and FSE sequences in test objects and in control hippocampi. In controls, the coefficient of variation of mean HCT2 values differed between slice positions, but was lowest for FF, followed by CSE data. The intrarater coefficient of reliability between repeated measurements in control subjects was lowest for FF HCT2, at 2.3%. The interrater coefficient of reliability for CSE HCT2 measurements in controls (4.8%) was slightly lower than the interrater coefficient for FF HCT2 (5.4%). HCT2 measurement with both CSE and FF identified abnormal values in the same 10 hippocampi of 12 patients. Hippocampal dual-echo T2 relaxometry using CSF nulling is reliable in control subjects, and identifies the abnormal hippocampi in patients with TLE. The increases in hippocampal T2 signal demonstrated using FF HCT2 measurements are unlikely to be partial volume effects from CSF.