T2 relaxometry of brain in myotonic dystrophy

We investigated the nature and extent of brain involvement in myotonic dystrophy (DM), examining possible T2 relaxation abnormalities in the brain of 20 patients with adult-onset DM and 20 sex- and age-matched normal controls. Brain MRI was performed at 0.5 T, and T2 values were calculated from signal intensity in two echoes. Regions of interest included: frontal, parietal, temporal, occipital and callosal (rostral and splenial) normal-appearing white matter; frontal, occipital, insular and hippocampal cortex; caudate nucleus, putamen, globus pallidus and thalamus. All white-matter and occipital and right frontal cortex regions showed a significantly longer T2 in the patients. Multiple regression analysis, including grey- and white-matter T2 as dependent variables, plus age at onset and at imaging, disease duration, muscular disability, brain atrophy and CTG trinucleotide repeats as independent variables, revealed that only white-matter T2 elongation and disease duration correlated positively. White-matter involvement in DM is more extensive than previously reported by MRI and neuropathological studies and seems to be progressive in the course of disease. Received: 31 May 2000 Accepted: 27 July 2000     

T2 relaxometry of normal pediatric brain development

Purpose

To establish normal age‐related changes in the magnetic resonance (MR) T₂ relaxation time constants of brain using data collected as part of the National Institutes of Health (NIH) MRI Study of Normal Brain Development.

Materials and Methods

This multicenter study of normal brain and behavior development provides both longitudinal and cross‐sectional data, and has enabled us to investigate T₂ evolution in several brain regions in healthy children within the age range of birth through 4 years 5 months. Due to the multicenter nature of the study and the extended period of data collection, periodically scanned inanimate and human phantoms were used to assess intra‐ and intersite variability.

Results

The main finding of this work, based on over 340 scans, is the identification and parameterization of the monoexponential evolution of T₂ from birth through 4 years 5 months of age in various brain structures.

Conclusion

The exponentially decaying T₂ behavior is believed to reflect the rapid changes in water content as well as myelination during brain development. The data will become publicly available as part of a normative pediatric MRI and clinical/behavioral database, thereby providing a basis for comparison in studies assessing normal brain development, and studies of deviations due to various neurological, neuropsychiatric, and developmental disorders. J. Magn. Reson. Imaging 2009;29:258–267. © 2009 Wiley‐Liss, Inc.     

T2 relaxometry of the hippocampus at 3T

BACKGROUND AND PURPOSE: T2 mapping is useful for identifying and quantifying abnormalities of the hippocampus and amygdala. It is particularly useful in the presurgical evaluation of patients with temporal lobe epilepsy and for the identification of bilateral hippocampal sclerosis (HS). The purpose of this study was to implement and validate a dual-echo method for producing coronal T2 maps with complete coverage of the hippocampus and the rest of the brain on a 3T MR imaging scanner. MATERIALS AND METHODS: T2 relaxation times were estimated on 10 occasions on 3 quality assessment Eurospin II (Diagnostic Sonar, Livingstone, Scotland) test objects with the use of conventional spin-echo (CSE), fast spin-echo, and fast recovery fast spin-echo (FRFSE) sequences on a 3T Excite MR imaging scanner (GE Healthcare, Milwaukee, Wis). Hippocampal T2 relaxation times were then measured in 15 healthy subjects and 20 subjects with clear-cut HS who were scanned at 1.5 T with a previously validated dual-echo CSE sequence and 3T with an FRFSE sequence. RESULTS: 3T FRFSE data were as reliable as CSE data at 1.5 T. Reliability of hippocampal T2 measures was good on healthy volunteers and subjects with HS. FRFSE images were suitable for qualitative radiologic reporting and with complete brain coverage, so no additional T2-weighted sequences were required. There was good correlation between the 3T hippocampal T2 measurements and values obtained with the previously validated technique at 1.5 T, with reliable identification of all of the subjects with HS. CONCLUSIONS: T2 mapping with an FRFSE 30/80 sequence may be readily applied at 3T and can produce reliable T2 values in vivo with contiguous 5-mm sections and in a much reduced scan time of 3 minutes 1 second compared with 10 minutes 30 seconds for the CSE sequence at 1.5 T.     

Human brain iron mapping using atlas‐based T2 relaxometry

Several in vivo quantitative MRI techniques have been proposed as surrogate measures to map iron content in the human brain. The majority of in vivo quantitative MRI iron mapping methods used the age‐dependent iron content data based on postmortem data. In this work, we fused atlas‐based human brain volumetry obtained on a large cohort of healthy adults using FreeSurfer with T₂ relaxation time measurements. We provide a brain atlas‐based T₂ relaxation time map, which was subsequently used along with published postmortem iron content data to obtain a map of iron content in subcortical and cortical gray matter. We have also investigated the sensitivity of the linear model relating transverse relaxation rate with published iron content to the number of regions used. Our work highlights the challenges encountered on using the simple model along with postmortem data to infer iron content in several brain regions where postmortem iron data are scant (e.g., corpus callosum, amygdale). Magn Reson Med, 2012. © 2011 Wiley Periodicals, Inc.     

T2 relaxometry of the infrapatellar fat pad after arthroscopic surgery

Objective

To investigate the T2 relaxation values of the infrapatellar fat pad (IFP) after arthroscopic surgery.

Materials and methods

This study was approved by the institutional review board; all individuals signed informed consent. We performed MRI in 16 knees from 8 subjects. Prior to imaging, each subject had unilateral arthroscopic knee surgery and an asymptomatic non-operated contralateral knee. We used a 10-echo multiple-TE fast-spin echo pulse sequence for creation of T2 relaxation time maps. Two musculoskeletal radiologists independently placed regions of interest in the IFP, suprapatellar subcutaneous and deep intermuscular adipose tissue. Qualitative assessments were performed to assess fibrotic changes affecting patellar retinaculum and IFP. Statistical analyses of T2 values determined differences between groups, correlation with time after surgery, and cut-off values to differentiate groups.

Results

The average time between arthroscopy and imaging was 3.5?±?0.4 years. IFP of knees with prior surgery had significantly shorter mean T2 values (133?±?14 ms) compared with control knees (147?±?8 ms, P?=?0.03). There was no significant difference between operated and control knees regarding T2 values of suprapatellar subcutaneous (P?=?0.3) or deep intermuscular adipose tissue (P?=?0.2). There was no correlation between IFP T2 values and time after surgery (P?>?0.2). IFP T2 values?≤?139 ms had 75 % sensitivity and 88 % specificity in identifying prior arthroscopy.

Conclusion

Shortening of T2 relaxation values is present in IFP chronically after arthroscopic surgery and may be an indicator of adipose tissue fibrosis.     

Human whole blood T2 relaxometry at 3 Tesla

A precise understanding of human blood spin–spin relaxation is of major importance for numerous applications, particularly functional magnetic resonance imaging (fMRI), which is increasingly performed at 3 Tesla. It is well known that T₂ measured from partially deoxygenated blood depends on the Carr–Purcell Meiboom–Gill (CPMG) refocusing interval (τ₁₈₀) and on blood oxygenation (Y), yet debate remains over the quantification of this phenomenon, primarily with respect to the accuracy of its characterization by the diffusion and fast two‐site exchange models. In this study, a detailed characterization of the deoxygenation‐induced T₂ reduction in human whole blood, as well as a comprehensive assessment of the role of τ₁₈₀, were performed at 3 T. The diffusion model was found to better fit the observed T₂ behavior as compared with the exchange model. The estimated diffusion‐model parameters suggest the T₂ decay enhancement at 3 T is due to a linear increase in the magnitude of deoxygenation‐induced field inhomogeneities with field strength. These findings also confirm the potential of τ₁₈₀ manipulation in measuring changes in venous blood volume. Magn Reson Med 61:249–254, 2009. © 2009 Wiley‐Liss, Inc.     

Limits of detection of SPIO at 3.0 T using T2 relaxometry.

T(2)* relaxometry for quantitative MR imaging is strongly hampered by large-scale field inhomogeneities, which lead to signal losses and an overestimation of the relaxation rate R(2)*. This is of particular importance for the sensitive detection of iron oxide contrast agent distributions. To derive an accurate measurement of T(2)*, a main field inhomogeneity correction is applied: the main field inhomogeneity is derived from multislice T(2)* relaxometry data and used as an initial value for an iterative optimization, by which the relaxation signal is corrected for each voxel. These corrected T(2)* maps show reduced influence of the local field variation and contain information about the local SPIO concentration. The method was tested on phantoms and the limit of detection of SPIO labeled cells using T(2)* relaxometry was estimated in volunteers to be 120 x 10(3) cells/mL (2.4 microg Fe/mL) in the brain and 385 x 10(3) cells/mL (8 microg Fe/mL) in the liver.     

Optimized clinical T2 relaxometry with a standard CPMG sequence

PURPOSE: To optimize the accuracy and precision of T2 measurements using the standard Carr-Purcell-Meiboom-Gill (CPMG) sequence. T2 values obtained with this technique are normally sensitive to imperfect refocusing due to the formation of unwanted stimulated echoes. MATERIALS AND METHODS: Modifications are made to the refocusing slice selection width and the interleaving scheme. A widened refocusing slice improves the uniformity of the refocusing flip angle across the slice. A slow spin echo acquisition provided "gold standard" T2 values. Repeated T2 measurements in phantom and human studies are used to compare the accuracy and precision of the optimized and non-optimized CPMG implementations. RESULTS: The required slice thickness ratio between refocusing and excitation slice widths is found to be 3:1 for typical optimized radiofrequency pulses. T2 values obtained using this optimized implementation more closely correspond to "gold standard" values. Repeated T2 measurements indicate significantly improved correspondence between data and model. A reduction in the fitting error of approximately 70% is demonstrated for phantoms. CONCLUSION: We demonstrate that a relatively simple change to the CPMG relaxometry sequence parameters from the default setup yields significant improvements in the accuracy and precision of T2 measurements.     

Multifocal low-signal brain lesions on T2*-weighted gradient-echo imaging

Multifocal small low-signal lesions on T2^*-weighted gradient-echo (GE) MRI are reported to be common in the brain of hypertensive patients. We examined factors associated with these lesions. For one year, we routinely obtained T2*-weighted GE images (TR 1000 TE 30 ms, flip angle = 20 °) in all adult patients (314) who underwent brain MRI in our hospital, using a 1.5 T superconducting magnet. Patients with multifocal small low-signal lesions with a known or presumed pathogenesis or any condition which may cause intracerebral haemorrhage, such as brain tumours, were excluded from further analysis. Thus, 191 cases remained (104 men and 87 women; age, 62.8 ± 11.0 years, range, 30–89 years). The overall prevalence of multifocal small low-signal lesions on the GE images was 15.2 % (29/191); they were commonly in the cerebral white matter and basal ganglia. They were detected in 12 (52.2 %) of the 23 patients with prior symptomatic brain hemorrhage, 12 (20.7 %) of the 58 with prior symptomatic infarcts, and only five (4.5 %) of 110 without a prior stroke. Logistic regression analysis indicated that multifocal small low-signal lesions were significantly correlated with a symptomatic acute brain haemorrhage (odds ratio, 13.17), chronic hypertension (4.00) and a symptomatic acute infarct (3.71). The association with symptomatic acute brain haemorrhage suggests that this finding may represent subclinical microhaemorrhage. The diagnostic potential of this finding to identify individuals at risk of symptomatic intracerebral haemorrhage may require further investigation. Received: 16 July 1999 Accepted: 23 August 1999     

Testing the three-pool white matter model adapted for use with T2 relaxometry.

A three-pool model was used to improve white-matter T2 relaxometry in low signal-to-noise (SNR) data. To verify the model very high SNR T2 relaxometry experiments were performed on myelinated tissue samples and three-pool fractions were consistently found. Relaxation curves based on the in vitro results were simulated with multiple SNRs and fit using the three-pool model and three less constraining nonnegative least squares-based methods. All methods performed well with noiseless data. At lower SNR values the three-pool model was superior, primarily due to the fact that the other methods often could not unambiguously calculate pool fractions.     

Increased anterior temporal lobe T2 times in cases of hippocampal sclerosis: a multi-echo T2 relaxometry study at 3 T

BACKGROUND AND PURPOSE: Increased T2 relaxation times in the ipsilateral hippocampus are present in patients with hippocampal sclerosis. Visual assessment of T2-weighted images of these patients suggests increased signal intensity in the anterior temporal lobe as well. Our aim was to assess hippocampal and anterior temporal T2 relaxation times in patients with partial epilepsy by using a new T2-relaxometry sequence implemented by using a 3-T General Electric imaging unit. METHODS: Coronal view T2 maps were generated by using an eight-echo Carr-Purcell-Meiboom-Gill sequence (TE, 28-231) with an acquisition time of 7 min on a 3-T General Electric Signa Horizon LX imaging unit. T2 relaxation times were measured in the hippocampus and anterior temporal lobe of 30 healthy control volunteers and 20 patients with partial epilepsy. RESULTS: For the 30 control volunteers, the mean hippocampal T2 relaxation time was 98 +/- 2.8 ms. In all measured areas, the asymmetry index was small (<0.01). For the 15 patients with independent evidence of hippocampal sclerosis established by visual, volumetric, and, when available, pathologic criteria, mean hippocampal T2 relaxation times were 118 +/- 7 ms (P <.0001) on the ipsilateral side and 101 +/- 4 ms (P =.005) on the contralateral side. The T2 values were also increased in the anterior temporal lobe (ipsilateral: 82 +/- 6 ms, P <.0001; contralateral: 79 +/- 6 ms, P =.01) as compared with the values for the control volunteers (75 +/- 3 ms). The five patients with focal cortical dysplasia had hippocampal T2 relaxation times that were not different from control values. CONCLUSION: T2 relaxometry at 3 T is feasible and useful and confirmed marked ipsilateral hippocampal signal intensity increase in patients with hippocampal sclerosis. Importantly, definite signal intensity change was also present in the anterior temporal lobe. T2 relaxometry is a sensitive means of identifying abnormalities in the hippocampus and other brain structures.     

Pattern of T2 hypointensity associated with ring-enhancing brain lesions can help to differentiate pathology

Ring-enhancing lesions seen on MR images can occur with a variety of etiologies. Some ring-enhancing lesions have hypointense rims peripherally on T2-weighted MR images. In this study, we examined whether T2 hypointense rims were associated with specific pathologies. A search for ring-enhancing lesions on MR images obtained from 1996 to 2004 was performed, and revealed 221 patients with MRI findings of ring enhancement. The pattern of T2 hypointensity (arc or rim) corresponding with ring enhancement was recorded. In addition, we analyzed other imaging characteristics, including signal on diffusion-weighted images, central homogeneity on T2 and multiplicity of lesions. We then reviewed clinical data on the patients to ascertain the diagnosis for each examination. The most common associated pathologies in our study were gliomas (40%), metastases (30%), abscesses (8%) and multiple sclerosis (MS; 6%). Hypointense borders on T2-weighted images were present in 67% of lesions in the form of a rim in 40% and an arc in 60%. Abscesses had the highest percentage of hypointense rims. Metastases and gliomas more commonly had arcs, and MS lesions were divided between rims and arcs. Abscesses and MS lesions were more commonly homogeneous centrally, compared to gliomas and metastases. Additionally, abscesses were more often bright on diffusion imaging than the other pathologies. As expected, abscesses and MS lesions were usually multiple, whereas metastases were typically multiple in approximately 50% of the patients; gliomas were generally solitary. Trends in T2 hypointensity may aid in distinguishing among etiologies of ring-enhancing lesions, although there is overlap between the MR appearance of these various pathologies.     

Serial postmortem relaxometry in the normal rat brain and following stroke

PURPOSE: To investigate MRI for noninvasive autopsy by means of measurements of serial changes in relaxation parameters of the rat brain during the postmortem interval. MATERIALS AND METHODS: Postmortem relaxometry measurements were performed before and hourly after death for 24 h on five control rats and five rats that underwent middle cerebral artery occlusion. Analyses were performed on representative regions of gray, white, and mixed gray/white matter structures. RESULTS: Significant decreases in both T(1) and T(2) values were measured in all areas in the control group within 24 h of death. In the stroke animals, T(2) differences between normal and ischemic striatal tissue decreased by 11 +/- 4% (P < 0.01), with a complete convergence of T(2) values observed between ischemic striatal tissue and nonischemic cortical tissue. CONCLUSION: Lesion conspicuity and the ability to differentiate between different tissue compartments are significantly affected by postmortem interval, and alterations to pulse timing parameters will be necessary if the sensitivity of MRI to detect central nervous system diseases in postmortem tissue is to be maintained. Indeed in the case of stroke at least, convergence of T(2) values with normal tissue post mortem indicates that T(1)-weighted images may be more sensitive to the presence of such lesions.