Inversion Recovery Echo Planar Research Articles

Development of fast multi‐slice apparent T1 mapping for improved arterial spin labeling MRI measurement of cerebral blood flow

To develop fast multi-slice apparent T1 (T1app ) mapping for accurate cerebral blood flow (CBF) quantification with arterial spin labeling (ASL) MRI. Fast multi-slice T1app was measured using a modified inversion recovery echo planar imaging (EPI) sequence with simultaneous application of ASL tagging radiofrequency (RF) and gradient pulses. The fast multi-slice T1app measurement was compared with the single-slice T1app imaging approach, repeated per slice. CBF was assessed in healthy adult Wistar rats (N = 5) and rats with acute stroke 24 hours after a transient middle cerebral artery occlusion (N = 5). The fast multi-slice T1app measurement was in good agreement with that of a single-slice T1app imaging approach (Lin's concordance correlation coefficient = 0.92). CBF calculated using T1app reasonably accounted for the finite labeling RF duration, whereas the routine T1 -normalized ASL MRI underestimated the CBF, particularly at short labeling durations. In acute stroke rats, the labeling time and the CBF difference (ΔCBF) between the contralateral normal area and the ischemic lesion were significantly correlated when using T1 -normalized perfusion calculation (R = 0.844, P = .035). In comparison, T1app -normalized ΔCBF had little labeling time dependence based on the linear regression equation of ΔCBF = -0.0247*τ + 1.579 mL/g/min (R = -0.352, P = .494). Our study found fast multi-slice T1app imaging improves the accuracy and reproducibility of CBF measurement.

Fast quantitative T1-mapping at ultra-high field using inversion-recovery echo planar imaging

Fast quantitative T1-mapping at ultra-high field using inversion-recovery echo planar imaging

Simultaneous measurement of tissue oxygen level-dependent (TOLD) and blood oxygenation level-dependent (BOLD) effects in abdominal tissue oxygenation level studies.

To assess oxygenation in abdominal organs with magnetic resonance imaging (MRI), a novel approach is presented to simultaneously measure both T1 - and T2*-maps serially during a single dynamic MRI scan in response to an oxygen challenge. The proposed acquisition scheme consists of a multishot multiecho gradient echo planar imaging sequence (ms-GEPI) interleaved with a multishot inversion recovery echo planar imaging (ms-IR-EPI) sequence. Respiratory motion compensation was accomplished with standard belt triggering and by acquiring all image data at the same phase of expiration. This respiratory-triggered, free-breathing, interleaved tissue oxygenation level-dependent (TOLD) and blood oxygenation level-dependent (BOLD) acquisition technique was validated on phantoms and seven healthy volunteers in response to an oxygen challenge. Measurements of relaxation times both in vitro and in vivo were in good agreement with those obtained using conventional pulse sequences and reported in the literature. The interleaved sequence was able to measure oxygen-induced relaxation time changes in human abdominal organs. The free-breathing respiratory-triggered interleaved T1 and T2* sequence successfully provided relaxation time maps of abdominal organs in a dynamic scan without the need for image registration. The simultaneous monitoring of tissue and blood oxygenation improves time efficiency and should enhance studies comparing dynamic T1 and T2* data within the abdomen.

Non‐invasive quantification of absolute cerebral blood volume during functional activation applicable to the whole human brain

Cerebral blood volume (CBV) changes in many diverse pathologic conditions, and in response to functional challenges along with changes in blood flow, blood oxygenation, and the cerebral metabolic rate of oxygen. The feasibility of a new method for non-invasive quantification of absolute cerebral blood volume that can be applicable to the whole human brain was investigated. Multi-slice data were acquired at 3 T using a novel inversion recovery echo planar imaging (IR-EPI) pulse sequence with varying contrast weightings and an efficient rotating slice acquisition order, at rest and during visual activation. A biophysical model was used to estimate absolute cerebral blood volume at rest and during activation, and oxygenation during activation, on data from 13 normal human subjects. Cerebral blood volume increased by 21.7% from 6.6 ± 0.8 mL/100 mL of brain parenchyma at rest to 8.0 ± 1.3 mL/100 mL of brain parenchyma in the occipital cortex during visual activation, with average blood oxygenation of 84 ± 2.1% during activation, comparing well with literature. The method is feasible, and could foster improved understanding of the fundamental physiological relationship between neuronal activity, hemodynamic changes, and metabolism underlying brain activation; complement existing methods for estimating compartmental changes; and potentially find utility in evaluating vascular health.

P846, a new gadolinium based low diffusion magnetic resonance contrast agent, in characterizing occlusive infarcts, reperfused ischemic myocardium and reperfused infarcts in rats

This study has two objectives: (1) to compare the kinetics of low diffusion P846 with Gd-DOTA using inversion recovery echo planar (IR-EPI) magnetic resonance (MR) imaging and (2) to determine the potential of P846 in defining myocardial viability in hearts subjected to various injuries using T1-weighted spin echo (T1-SE). Rats were subjected to (1) occlusive infarcts (n = 16), (2) reperfused ischemic injuries (n = 8) or (3) reperfused infarcts (n = 16). A dose of 0.05 mmol/kg P846 was compared to 0.1 mmol/kg Gd-DOTA. IR-EPI and T1-SE images were obtained during 60 min. T(1), DeltaR(1) and DeltaR(1) ratio were measured on IR-EPI. Infarct extents were evaluated on T1-SE and compared with histochemical staining. Blood DeltaR(1) was higher at 5 min after P846 (6.36 +/- 0.32 s(-1)) than after Gd-DOTA (1.30 +/- 0.14 s(-1); P < 0.001). With P846, occlusive infarcts appeared as a hypoenhanced region surrounded by a hyperenhanced rim that lasted for 60 min. The increase in the DeltaR(1) ratio value was slower after P846 than with Gd-DOTA in the reperfused infarcts, suggesting low diffusion/convection of P846. Gd-DOTA homogenously enhanced both occlusive and reperfused infarcts at 30 min. P846 provides better contrast and extended discrimination between occlusive and reperfused infarcts compared with Gd-DOTA. The gadolinium dose could be reduced with P846.

Water proton T 1 measurements in brain tissue at 7, 3, and 1.5T using IR-EPI, IR-TSE, and MPRAGE: results and optimization

This paper presents methods of measuring the longitudinal relaxation time using inversion recovery turbo spin echo (IR-TSE) and magnetization-prepared rapid gradient echo (MPRAGE) sequences, comparing and optimizing these sequences, reporting T1 values for water protons measured from brain tissue at 1.5, 3, and 7 T. T1 was measured in cortical grey matter and white matter using the IR-TSE, MPRAGE, and inversion recovery echo planar imaging (IR-EPI) pulse sequences. In four subjects the T1 of white and grey matter were found to be 646+/-32 and 1,197+/-134 ms at 1.5 T, 838+/-50 and 1,607+/-112 ms at 3T, and 1,126+/-97, and 1,939+/-149 ms at 7 T with the MPRAGE sequence. The T1 of the putamen was found to be 1,084+/-63 ms at 1.5 T, 1,332+/-68 ms at 3T, and 1,644+/-167 ms at 7 T. The T1 of the caudate head was found to be 1,109+/- 66 ms at 1.5 T, 1,395+/-49 ms at 3T, and 1,684+/-76 ms at 7 T. There was a trend for the IR-TSE sequence to underestimate T1 in vivo. The sequence parameters for the IR-TSE and MPRAGE sequences were also optimized in terms of the signal-to-noise ratio (SNR) in the fitted T1. The optimal sequence for IR-TSE in terms of SNR in the fitted T1 was found to have five readouts at TIs of 120, 260, 563, 1,221, 2,647, 5,736 ms and TR of 7 s. The optimal pulse sequence for MPRAGE with readout flip angle = 8 degrees was found to have five readouts at TIs of 160, 398, 988, 2,455, and 6,102 ms and a TR of 9 s. Further optimization including the readout flip angle suggests that the flip angle should be increased, beyond levels that are acceptable in terms of power deposition and point-spread function.

EPI-FLAIR sequence in the evaluation of mesial temporal sclerosis

The purpose of this study is to evaluate morphological and signal intensity changes in the hippocampus in patients with medically intractable temporal lobe epilepsy. We studied 8 patients with mesial temporal sclerosis using a 1.5 -T MR and the following sequences Spin Eco- SE, Fast Spin Echo- FSE, Fluid Attenuation Inversion Recovery Echo Planar Imaging--FLAIR-EPI. We noticed a sensitive increase signal intensity on FLAIR- EPI sequences, particularly, in coronal images, than on SE and FSE sequences. The STIR sequence showed a cortical hippocampus atrophy in half of the cases, in whom signal abnormalities were present.

Quantification of tissue gadolinium concentration using magnetic resonance imaging: comparison of ultrashort inversion time inversion recovery echoplanar and dynamic three-dimensional spoiled gradient-recalled approaches with in vitro measurements.

Quantification of tissue gadolinium concentration using magnetic resonance imaging: comparison of ultrashort inversion time inversion recovery echoplanar and dynamic three-dimensional spoiled gradient-recalled approaches with in vitro measurements.

Identification of myocardial reperfusion with echo planar magnetic resonance imaging. Discrimination between occlusive and reperfused infarctions.

The current treatment of many cases of acute myocardial infarction involves the use of thrombolytic agents. Evaluation of this therapy requires determination of the success of reperfusion and assessment of the presence and extent of infarction in the reperfused territory. The present study was designed to simulate in rat models several possible outcomes of reperfusion therapy: (1) successful reperfusion and absence of myocardial infarction, (2) successful reperfusion and presence of myocardial infarction, and (3) unsuccessful reperfusion. The usefulness of contrast-enhanced fast magnetic resonance (MR) imaging in defining the success of reperfusion was investigated. The dynamic effects were examined of low and high doses of gadolinium-BOPTA/dimeglumine (Gd-BOPTA/dimeg) on myocardial signal using MR inversion recovery echo planar imaging (IR-EPI) and gradient recalled echo planar imaging (GR-EPI), respectively. Rats were subjected to one of the following regimens: reperfused reversible myocardial injury (n = 9), reperfused irreversible myocardial injury (n = 9), and occlusive infarction (n = 9). MR echo planar images were acquired every 1 or 2 seconds before, during, and after administration of Gd-BOPTA/dimeg. In all groups, normal myocardial signal was sharply increased on IR-EPI and decreased on GR-EPI at the peak of the bolus, followed by a gradual decline to baseline. In animals subjected to reperfused reversible myocardial injury, normal and previously ischemic regions were indistinguishable during and after the passage of Gd-BOPTA/dimeg. On the other hand, enhancement of reperfused irreversibly injured myocardium was delayed but increased steadily to a higher level than normal myocardium on IR-EPI. The reperfused irreversibly injured myocardium was identified on IR-EPI as a zone of high signal (hot spot). On GR-EPI, signal loss in reperfused irreversibly injured myocardium was significantly less compared with normally perfused myocardium. In animals with occlusive infarctions, there was no change in signal intensity over the ischemic region on either IR-EPI or GR-EPI. Occlusive infarction was identified as zones of either low (cold spot) or high (hot spot) signal compared with normal myocardium, depending on MR pulse sequence and dose of the contrast medium. The transit of Gd-BOPTA/dimeg monitored by fast MR imaging techniques can be used to distinguish between reperfused reversibly and reperfused irreversibly injured myocardium and between occlusive and reperfused infarctions.