Purpose:To investigate the potential value and relationship of in vivo quantification of apparent diffusion coefficients (ADCs) and T2 relaxation times for characterizing brain tumor cellularity and tumor-related edema. Materials and Methods:A total of 26 patients with newly diagnosed gliomas, meningiomas, or metastases underwent diffusion-weighted and six-echo multisection T2-preparation imaging. Regions of interest (ROIs) were drawn on conventional MR images to include tumor (as defined by contrast agent enhancement) and immediate and peripheral edema. Areas of necrosis were excluded. Median values of ADCs and T2 in the ROIs were calculated.Results: ADCs for gliomas were similar to those for meningiomas or metastases in all regions. Tumor T2 values for gliomas (159.5 Ϯ 30.6 msec) were significantly higher than those for meningiomas or metastases (125.0 Ϯ 31.1 msec; P ϭ 0.005). Immediate-edema T2 values for meningiomas or metastases (226.0 Ϯ 44.1 msec) were significantly higher than those for gliomas (203.5 Ϯ 32.8 msec; P ϭ 0.033). Peripheral-edema T2 values for gliomas (219.5 Ϯ 41.9 msec) were similar to those for meningiomas or metastases (202.5 Ϯ 26.5 msec; P ϭ 0.377). Both immediate-and peritumoral-edema ADCs and T2 values were significantly higher than those in tumor for both tumor types. ADCs and T2 values from all regions correlated significantly for gliomas (r ϭ 0.95; P Ͻ 0.0001) and for meningiomas or metastases (r ϭ 0.81; P Ͻ 0.0001). Conclusion:The higher immediate-edema T2 values for nonglial tumors than for gliomas suggest tumor-related edema (vasogenic vs. infiltrated) can be further characterized by using T2 values. There were significant correlations between ADC and T2 values.

Background-More than 50% of >270 000 childhood cancer survivors in the United States have been treated with anthracyclines and are therefore at risk of developing cardiotoxicity. Cardiac magnetic resonance (CMR) has demonstrated utility to detect diffuse interstitial fibrosis and changes in regional myocardial function. We hypothesized that CMR would identify occult cardiotoxicity characterized by structural and functional myocardial abnormalities in a cohort of asymptomatic pediatric cancer survivors with normal global systolic function. Methods and Results-Forty-six long-term childhood cancer survivors with a cumulative anthracycline dose ≥200 mg/m 2 and normal systolic function were studied 2.5 to 26.9 years after anthracycline exposure. Subjects underwent transthoracic echocardiography, CMR with routine cine acquisition, tissue characterization, and left ventricular strain analysis using a modified 16-segment model. Extracellular volume was measured in 27 subjects, all of whom were late gadolinium enhancement negative. End-systolic fiber stress was elevated in 45 of 46 subjects. Low average circumferential strain magnitude (ε cc ) −14.9±1.4; P<0.001, longitudinal strain magnitude (ε ll ) −13.5±1.9; P<0.001, and regional peak circumferential strain were seen in multiple myocardial segments, despite normal global systolic function by transthoracic echocardiography and CMR. The mean T1 values of the myocardium were significantly lower than that of control subjects at 20 minutes (458±69 versus 487±44 milliseconds; P=0.01). Higher mean extracellular volume was observed in female subjects (0.34 versus 0.22; P=0.01). The purpose of this study was to use CMR T1 mapping techniques and measures of myocardial strain by tagged cine MRI to detect interstitial disease and changes in regional myocardial function in childhood cancer survivors. We tested the hypothesis that individuals with a history of high-dose anthracycline therapy may have occult cardiotoxicity, manifested by a decrease in circumferential ε cc and longitudinal ε ll strain magnitude and changes in myocardial T1 and ECV, despite normal standard measures of global left ventricular (LV) systolic function. Conclusions-Asymptomatic Methods Study PopulationEligible subjects with a cumulative anthracycline dose ≥200 mg/m 2 and normal LV systolic function defined as TTE-based shortening fraction ≥29% were identified and prospectively enrolled through a registry of pediatric cancer survivors treated with anthracyclines between 1985 and January 2011. Inclusion criteria for this study are shown in Figure 1. Subjects with high-dose radiation exposure to the chest (>3000 cGy) were excluded from the study to minimize the known synergistic effect of therapeutic radiation on cardiotoxicity. 5,21This study was approved by the Institutional Review Board at the Connecticut Children's Medical Center. The medical records of all enrolled subjects were reviewed to identify known risk factors associated with cardiotoxicity. Conversions to isotoxic equivalents of anthracycline a...

Cardiac arrhythmias reflect abnormal electric activity in the heart. Radiofrequency ablation (RFA) is used to treat different arrhythmias by thermally damaging tissue regions and eliminating irregular action potential propagation paths. To ensure a permanent electric block, RFA must create a continuous line of transmural lesions.1 Notwithstanding extensive efforts, the success rates of the RFA operations are still low, 2 likely because of the lack of tools to validate the lesion extent. Current ablation methods rely on suboptimal fluoroscopy and electrophysiology electroanatomic systems; fluoroscopy has poor soft tissue contrast, and even with electroanatomic systems locating and characterizing the ablation lesions are challenging. More importantly, it is difficult to predict which of the lesions that yield a conduction block in the acute setting will maintain a block in the chronic setting. Clinical Perspective on p 727MRI is a powerful tool to detect ablation lesions because of its high soft tissue contrast. Double inversion fast spin echo (DIR) sequence demonstrates intrinsic T 2 -weighted contrast and quickly detect lesions, but DIR images lack specificity and provide poor border visibility. 3,4 Late gadolinium enhancement (LGE) methods provide high contrast between healthy myocardium and the ablation lesions. 3,[5][6][7] However, acute lesion appearance on the LGE image varies with the time between the Gd-DTPA injection and image acquisition because of the wash-in/wash-out kinetics, 7 particularly in areas associated with microvascular obstruction. Shortly after Gd-DTPA injection, the lesion contains hypoenhanced regions in typical LGE acquisitions. Then Gd-DTPA starts to enter the lesion, and a bright rim becomes visible. As the bright rim expands toward the center of the lesion over the ensuing minutes, wash-out mechanisms also begin to diminish the contrast at the outer border of the lesion. The lesion severity can also affect the wash-in/wash-out kinetics. As a second consideration, a recent study reported that the scar size measured 3 months after ablation with LGE images is <50% of that measured acutely. 6 One of the possible reasons for this © 2014 American Heart Association, Inc. Original ArticleBackground-Both intrinsic contrast (T 1 and T 2 relaxation and the equilibrium magnetization) and contrast agent (gadolinium)-enhanced MRI are used to visualize and evaluate acute radiofrequency ablation lesions. However, current methods are imprecise in delineating lesion extent shortly after the ablation. Methods and Results-Fifteen lesions were created in the endocardium of 13 pigs. A multicontrast inversion recovery steady state free precession imaging method was used to delineate the acute ablation lesions, exploiting T 1 -weighted contrast. T 2 and M o * maps were also created from fast spin echo data in a subset of pigs (n=5) to help characterize the change in intrinsic contrast in the lesions. Gross pathology was used as reference for the lesion size comparison, and the lesion structures were confirm...

Introduction: Blood oxygen level-dependent (BOLD) magnetic resonance imaging (MRI) during manipulation of inhaled carbon dioxide (CO₂) can be used to measure cerebrovascular reactivity (CVR) and map regions of exhausted cerebrovascular reserve. These regions exhibit a reduced or negative BOLD response to inhaled CO₂. In this study, we sought to clarify the mechanism behind the negative BOLD response by investigating its time delay (TD). Dynamic susceptibility contrast (DSC) MRI with the injection of a contrast agent was used as the gold standard in order to provide measurement of the blood arrival time to which CVR TD could be compared. We hypothesize that if negative BOLD responses are the result of a steal phenomenon, they should be synchronized with positive BOLD responses from healthy brain tissue, even though the blood arrival time would be delayed. Methods: On a 3-tesla MRI system, BOLD CVR and DSC images were collected in a group of 19 patients with steno-occlusive cerebrovascular disease. For each patient, we generated a CVR magnitude map by regressing the BOLD signal with the end-tidal partial pressure of CO₂ (P_ETCO₂), and a CVR TD map by extracting the time of maximum cross-correlation between the BOLD signal and P_ETCO₂. In addition, a blood arrival time map was generated by fitting the DSC signal with a gamma variate function. ROI masks corresponding to varying degrees of reactivity were constructed. Within these masks, the mean CVR magnitude, CVR TD and DSC blood arrival time were extracted and averaged over the 19 patients. CVR magnitude and CVR TD were then plotted against DSC blood arrival time. Results: The results show that CVR magnitude is highly correlated to DSC blood arrival time. As expected, the most compromised tissues with the longest blood arrival time have the lowest (most negative) CVR magnitude. However, CVR TD shows a noncontinuous relationship with DSC blood arrival time. CVR TD is well correlated to DSC blood arrival time (p < 0.0001) for tissue of positive reactivity, but fails to maintain this trend for tissue of negative reactivity. Regions with negative reactivity have similar CVR TD than healthy regions. Conclusion: These results support the hypothesis that negative reactivity is the result of a steal phenomenon, lowering the BOLD signal as soon as healthier parts of the brain start to react and augment their blood flow. BOLD CVR MRI is capable of identifying this steal distribution, which has particular diagnostic significance as it represents an actual reduction in flow to already compromised tissue.

Auto-triggered elliptic centric-ordered three-dimensional (3D) gadolinium-enhanced magnetic resonance (MR) angiography was compared with 3D multiple overlapping thin-slab acquisition time-of-flight (TOF) MR angiography in the evaluation of intracranial arteriovenous malformations (AVMs) in 10 patients. Intraarterial digital subtraction angiography (DSA) was the reference standard. Gadolinium-enhanced MR angiograms were found to be equivalent to DSA images in AVM component depiction in 70%--90% of cases and were consistently superior to TOF MR angiograms.

A modified Look-Locker acquisition using saturation recovery (MLLSR) for breath-held myocardial T 1 mapping is presented. Despite its reduced dynamic range, saturation recovery enables substantially higher imaging efficiency than conventional inversion recovery T 1 mapping because it does not require time for magnetization to relax to equilibrium. Therefore, MLLSR enables segmented readouts, shorter data acquisition windows, and shorter breath holds compared with inversion recovery. T 1 measurements in phantoms using MLLSR showed a high correlation with conventional single-point inversion recovery spin echo. In vivo T 1 measurements from normal and infarcted myocardium in 41 volunteers and patients were consistent with previously reported values. Twenty subjects were also scanned with MLLSR using an accelerated sampling scheme that required half the scan time (eight vs. 16 heartbeats) but yielded equivalent results The longitudinal magnetization relaxation time T 1 has long been used to characterize tissue and pathology (1-7). For cardiac applications, it has more recently been demonstrated as a noninvasive means for quantifying acute and chronic myocardial infarction (8-11), diffuse fibrosis (12-14), heart failure (15), and myocardial amyloidosis (16). Although T 1 -weighted imaging, such as delayed enhancement MRI (DE-MRI), is part of routine clinical cardiac MR, an inappropriate selection of the inversion time (TI) in these methods result in poor contrast between normal and abnormal myocardium. Furthermore, quantitative analysis of T 1 -weighted images, such as for infarct sizing (17) and gray zone characterization (18), is limited by the qualitative signal intensity variations in individual images. In comparison, T 1 mapping can overcome these limitations and provide the underlying quantitative tissue property of the different types of normal and abnormal myocardium.Because of the growing interest in characterizing the physical properties of myocardium directly through T 1 measurement rather than indirectly through T 1 -weighted imaging, a number of approaches for T 1 mapping have recently been proposed. Iles et al. (12) presented a technique that generates a sequence of rapid inversion recovery (IR) images with increasing TIs. To produce an adequate number of time points, up to four breath holds were necessary; thus, image registration was impacted by the multiple breath holds and changing image planes. Blume et al. (9) demonstrated a navigator-gated IR technique that simultaneously measured myocardial T 1 and T 2 . Because the maximum measured TI was limited by the mid-diastolic trigger delay, it had a heart rate dependence that could affect the accuracy of the T 1 calculation, particularly for postcontrast T 1 s. Using a modification of the Look-Locker (LL) method, the modified look-locker inversion recovery (MOLLI) technique (19,20) acquires single-shot images at 11 TIs spanning five cardiac cycles in a single breath hold. As with other IR-based cardiac T 1 mapping techniques, the greatest limitation of ...

Variable-density (VD) spiral k-space acquisitions are used to acquire high-resolution (0.78 mm), motion-compensated images of the coronary arteries. Unlike conventional methods, information for motion compensation is obtained directly from the coronary anatomy itself. Specifically, periods of minimal coronary distortion are identified by applying the correlation coefficient template matching algorithm to real-time images generated from the inner, high-density portions of the VD spirals. Combining the data associated with these images together, high-resolution, motion-compensated coronary images are generated. Because coronary motion is visualized directly, the need for cardiac-triggering, breath-holding, and navigator echoes is eliminated. The motion compensation capability of the technique is determined by the inner-spiral spatial and temporal resolution. Results indicate that the best performance is achieved using inner-spiral images with high spatial resolution (1.6 -2.9 mm), even though temporal resolution (four to six independent frames per second) suffers as a result. Image quality within the template region in healthy volunteers was found to be comparable to that achieved with cardiac-triggered breath-hold scans, although Key words: variable-density; template matching; coronary artery; motion compensation; real-time Diagnostic-quality MR coronary images must possess submillimeter spatial resolution. While the theoretical limits of MR do not preclude the attainment of such resolutions, respiratory-(1) and cardiac-(2) induced displacement and distortion (3) of the arteries can significantly degrade image quality. To counteract these effects, motion compensation schemes have been developed (4,5). With the evolution toward higher-resolution imaging, however, a number of concerns are arising with respect to their accuracy. Most of these approaches use indirect measures such as the position of bellows placed over the chest, ECG waveforms, and diaphragm position determined by navigator echoes to infer coronary motion. Recent studies have indicated that while indirect measures may correlate with coronary displacement, they do not give a precise characterization of the actual motion (1,6,7). Additionally, indirect measures generally do not give any indication of the degree of distortion associated with the coronary motion (3). Furthermore, arrhythmias and/or difficulties in breathholding, commonly found in patients with coronary disease, give rise to added difficulties in the application of these techniques (8).A technique that makes use of direct visualization of the coronary anatomy for motion compensation was developed recently by Hardy et al. (9). In this "adaptive averaging" technique, a series of interleaved high-resolution echo-planar images are acquired. From each of the individual interleaves, aliased "subimages" are formed. Since these subimages are generated from every interleaf, they provide real-time visualization of the coronary anatomy. Each subimage is used to evaluate the motion present during the...

The optimal b value for in vivo DT MRI and tractographic assessment of human skeletal muscle in the calf at 1.5 T MRI was found to be 625 s/mm(2).