To determine the ability of proton nuclear magnetic resonance imaging (NMRI) to detect early myocardial ischemic injury, a ligature was placed around the anterior descending (3) or circumflex(3) artery in 6 dogs. In vivo imaging was done at end diastole using a .15T (6.25MHz) resistive NMR unit prior to and for 4-6 hours after coronary artery occlusion. Image acquisition was by spin echo (SE) (TE 30 msec TR 1sec, TE 60 msec TR>1sec) and inversion recovery (IR) pulse sequences. Compared to normal surrounding myocardium, NMR signal increased within the ischemic zone. Changes of evolving infarction by microscopic examination of the excised heart correlated well with the extent of NMR changes. Excellent visualization of the ischemic zone was obtained using the SE technique, particularly the TE 60 msec SE sequence. IR imaging did not demonstrate ischemia. T2 of ischemic myocardium was increased 50 +- 3% above normal myocardium in the first hour and 78 +- 27% in the third hour post occlusion (p<.05). The authors conclude that NMRI can detect early myocardial ischemic injury, best with the TE 60 msec SE sequence, thus providing a potential tool for evaluating the efficacy of interventions to limit myocardial infarct size.
The radiation dose to the lung from the administration of Tc-99m sulfur colloid aerosol (for ventilation investigations) has been calculated. The dose to the ciliated airway epithelium varies between 0.34 to 2.5 rads, compared with 0.31 rads to the lung parenchyma. The calculation was normalized to a total of 1 mCi of Tc-99m deposited in the lung.
BackgroundBOLD CMR is a non-contrast approach for examining myocardial perfusion but despite major technical advancements to date, its reliability remains weak.A key reason for this is the unpredictable cardiac motion during stress, which can lead to pronounced artifacts that confound/ mask the true BOLD signal changes during hyperemia.Recently, regadenoson has become the vasodilator of choice owing to greater patient tolerability and ease of use.We hypothesized that at 10-mins post regadenoson administration (p.r.a),(a) BOLD CMR artifacts at stress are markedly reduced compared to those conventionally acquired at 2-mins p.r.a; and (b) that myocardial perfusion reserve (MPR) remains greater than 2.0 and is highly correlated with the BOLD effects estimated from T 2 maps.
A new method for computing the modulation transfer function (MTF) of magnetic resonance (MR) imagers is presented. Previous attempts to compute the MTF of MR imagers used nonlinear magnitude reconstructed images, resulting in erroneous MTFs. By using complex domain images, the new method produces predisplay MTFs which describe the spatial frequency transfer characteristics of the entire image formation process, except the magnitude operator, eliminating the artifacts previously found in MR imager MTFs. The use of complex domain images results in two‐sided MTFs which differentiate the positive and negative frequencies associated with positive and negative phase encoding or positive and negative time relative to the echo formation. Experimental results are presented which confirm the theoretically predicted form of MR imager MTFs and the need for two‐sided MTFs.
Introduction: T2* cardiac MRI (CMR) is the standard for detecting hemorrhagic myocardial infarction (MI). However, the conventional T2* CMR (2D breath-held, ECG-gated, multi-gradient-echo T2*) can suffer from limited spatial resolution and multiple motion artifacts. We developed a time-efficient, fully ungated, free breathing, 3D T2* mapping method for detecting and characterizing hemorrhagic MI (hMI). Methods: Our approach, developed using a low-rank tensor framework, was tested in a canine model with reperfused hMI. Animals (n=5) underwent CMR 3 days after reperfusion. Short-axis, conventional 2D and proposed 3D T2*-w images, and the corresponding LGE images were acquired in a 3T CMR system. T2* maps (8 echoes, 1.41-15.44 ms) were constructed using mono-exponential fitting. IMH extent was determined by measuring the weighted sum of the imaging slices with hypointense regions (based on ‘mean-2SD’ criterion) within the LGE positive territories. Image quality was assessed by two CMR experts using a Likert scale (1 – poor; and 5 - excellent). Results: Figure 1 shows representative conventional 2D, proposed 3D T2* images, along with LGE image for reference. T2* image scores were higher with the proposed than the conventional approach: 3.5 ± 0.5 (conventional) vs 3.8 ± 0.3 (proposed), p<0.05. IMH extent measured using the two approaches provided equivalent IMH extent (see Fig. 2) under stable imaging conditions. Conclusions: The proposed 3D T2* mapping can provide much needed improvement in image quality compared to conventional 2D T2* CMR for detection of hemorrhagic MI without the need for breath holding or cardiac gating, both of which are known problems in acute MI patients. Provided imaging conditions are favorable, we also found that the proposed and conventional methods yield equivalent estimates of IMH extent. Additional studies are needed to evaluate the benefits of the proposed approach in clinical setting.
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