Monitoring Tumor Therapy

This unit presents the preferred protocol for imaging the brain following the institution of chemotherapy, radiation therapy, or surgery for brain tumors and specific modifications are discussed where necessary. The sequences described in this unit are based on a 1.5 T scanner (Echospeed GE Medical Systems), but can be expected to be equally applicable to other field strengths and scanners from other manufacturers.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/145339/1/cpmia0305.pd

Cardiac T-2* mapping:Techniques and clinical applications

Cardiac T-2* mapping is a noninvasive MRI method that is used to identify myocardial iron accumulation in several iron storage diseases such as hereditary hemochromatosis, sickle cell disease, and beta-thalassemia major. The method has improved over the years in terms of MR acquisition, focus on relative artifact-free myocardium regions, and T-2* quantification. Several improvement factors involved include blood pool signal suppression, the reproducibility of T-2* measurement as affected by scanner hardware, and acquisition software. Regarding the T-2* quantification, improvement factors include the applied curve-fitting method with or without truncation of the signals acquired at longer echo times and whether or not T-2* measurement focuses on multiple segmental regions or the midventricular septum only. Although already widely applied in clinical practice, data processing still differs between centers, contributing to measurement outcome variations. State of the art T-2* measurement involves pixelwise quantification providing better spatial iron loading information than region of interest-based quantification. Improvements have been proposed, such as on MR acquisition for free-breathing mapping, the generation of fast mapping, noise reduction, automatic myocardial contour delineation, and different T-2* quantification methods. This review deals with the pro and cons of different methods used to quantify T-2* and generate T-2* maps. The purpose is to recommend a combination of MR acquisition and T-2* mapping quantification techniques for reliable outcomes in measuring and follow-up of myocardial iron overload. The clinical application of cardiac T-2* mapping for iron overload's early detection, monitoring, and treatment is addressed. The prospects of T-2* mapping combined with different MR acquisition methods, such as cardiac T-1 mapping, are also described. Technical Efficacy Stage: 5 J. Magn. Reson. Imaging 2019

Influence of reference tube location on the measured sodium concentrations in calf muscles using a birdcage coil at 3T

PURPOSE: To investigate the influence of the sodium (Na) reference tube location in a birdcage coil on the quantification of Na in the calf muscle. Two correction methods were also evaluated. METHOD: Eight (4 × 20 mM, 4 × 30 mM Na) reference tubes were placed along the inner surface of the coil and one (30 mM Na) tube more centrally near the tibia. In two volunteers, four repeated UTE scans were acquired. In six calf muscles, the Na concentration was calculated based on each reference tube. Flip angle mapping of a homogenous Na phantom was used for correcting intensity values. Alternatively, a normalized intensity map was used for correcting the in vivo signal intensities. Results were given as range or SD of Na concentration measurements over the reference tubes. RESULTS: For calf Na measurements, there was limited space for positioning reference tubes away from coil B1 inhomogeneity. In both volunteers, the Na quantification depended greatly on the reference tube used with a range of up to 10 mM. The central tube location gave a Na quantification close to the mean of the other tubes. The flip angle and normalized signal intensity phantom-based correction methods decreased the quantification variation from 14.9% to 5.0% and 10.4% to 2.7%, respectively. Both correction methods had little influence (&lt; 2.3%) on quantification based on the central tube. CONCLUSION: Despite use of a birdcage coil, location of the reference tube had a great impact on Na quantification in the calf muscles. Although both correction methods did reduce this variation, placing the reference tube more centrally was found to give the most reliable results.</p

T2* assessment of the three coronary artery territories of the left ventricular wall by different monoexponential truncation methods

OBJECTIVES: This study aimed at evaluating left ventricular myocardial pixel-wise T2* using two truncation methods for different iron deposition T2* ranges and comparison of segmental T2* in different coronary artery territories. MATERIAL AND METHODS: Bright blood multi-gradient echo data of 30 patients were quantified by pixel-wise monoexponential T2* fitting with its R2 and SNR truncation. T2* was analyzed at different iron classifications. At low iron classification, T2* values were also analyzed by coronary artery territories. RESULTS: The right coronary artery has a significantly higher T2* value than the other coronary artery territories. No significant difference was found in classifying severe iron by the two truncation methods in any myocardial region, whereas in moderate iron, it is only apparent at septal segments. The R2 truncation produces a significantly higher T2* value than the SNR method when low iron is indicated. CONCLUSION: Clear T2* differentiation between the three coronary territories by the two truncation methods is demonstrated. The two truncation methods can be used interchangeably in classifying severe and moderate iron deposition at the recommended septal region. However, in patients with low iron indication, different results by the two truncation methods can mislead the investigation of early iron level progression

Intra‐Axial Primary Brain Tumors

The majority of primary brain tumors in adults are found in the supratentorial compartment, while tumors in pediatric patients are usually infratentorial in location. This unit presents basic protocols for imaging all types of primary intra‐axial brain tumors, whether infiltrative (i.e., astrocytoma, oligodendroglioma, lymphoma) or circumscribed (i.e., ganglioglioma, cystic astrocytoma). Specific modifications are discussed where necessary. The sequences described in this unit are based on a 1.5 T scanner (Echospeed GE Medical Systems), but can be expected to be equally applicable to other field strengths and scanners from other manufacturers.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/145224/1/cpmia0303.pd

Correlation between choline level and Gd-DTPA enhancement in patients with brain metastases of mammary carcinoma

Single voxel 1HH double spin-echo MR spectroscopy was used to examine 15 cases of brain metastasis of mammary carcinoma (18 lesions) in relation to Gd-DTPA enhanced MR imaging. For lesions larger than 50% of MRS voxel size, there was significant correlation between Gd-DTPA-enhanced MRI signal and MRS-detected signal of choline (Cho) containing compounds (r = 0.86, P < 0.01; n = 8). The observed loss of correlation when including the smaller lesions was overcome by correcting for partial volume effects (r = 0.69, P < 0.002; n = 18). Metastasis spectra showed increased Cho compared with control spectra, except for those lesions showing detectable lactate (Lact) signal. The detection of Lact in four of the larger lesions coincided with comparatively low levels of creatine (Cr) and Cho and heterogeneous Gd-DTPA enhancement (ring-enhancement). It was concluded that in brain metastases of mammary carcinoma Lact represents a product of ischemia preceding/during tissue decay resulting in central necrosis, rather than tumor specific metabolism resulting in increas

Diagnostic value of MRS-quantified brain tissue lactate level in identifying children with mitochondrial disorders

Magnetic resonance spectroscopy (MRS) of children with or without neurometabolic disease is used for the first time for quantitative assessment of brain tissue lactate signals, to elaborate on previous suggestions of MRS-detected lactate as a marker of mitochondrial disease. Multivoxel MRS of a transverse plane of brain tissue cranial to the ventricles was performed in 88 children suspected of having neurometabolic disease, divided into 'definite' (n = 17, >= 1 major criteria), 'probable' (n = 10, >= 2 minor criteria), 'possible' (n = 17, 1 minor criterion) and 'unlikely' mitochondrial disease (n = 44, none of the criteria). Lactate levels, expressed in standardized arbitrary units or relative to creatine, were derived from summed signals from all voxels. Ten 'unlikely' children with a normal neurological exam served as the MRS reference subgroup. For 61 of 88 children, CSF lactate values were obtained. MRS lactate level (> 12 arbitrary units) and the lactate-to-creatine ratio (L/Cr > 0.22) differed significantly between the definite and the unlikely group (p = 0.015 and p = 0.001, respectively). MRS L/Cr also differentiated between the probable and the MRS reference subgroup (p = 0.03). No significant group differences were found for CSF lactate. MRS-quantified brain tissue lactate levels can serve as diagnostic marker for identifying mitochondrial disease in children. MRS-detected brain tissue lactate levels can be quantified. MRS lactate and lactate/Cr are increased in children with mitochondrial disease. CSF lactate is less suitable as marker of mitochondrial disease