T2* effects in the dual‐sequence method for high‐dose first‐pass myocardial perfusion

Abstract

Purpose: To examine whether T2* effects reduce the accuracy of arterial input function (AIF) measurement by the dual-sequence method. Materials and Methods:The dual-sequence method obtains a low-resolution AIF image and high-resolution myocardial images in each cycle, with suitable T1 weightings. It was modified to assess T2* effects in the low-resolution AIF image (4.8 ϫ 4.8 ϫ 10 mm voxels, TE ϭ 0.58 msec) by minimizing T1 weighting in that sequence, while the myocardial sequence remained T1-weighted. In 10 patients who underwent perfusion MRI scans (0.5 M Magnevist, 0.1 mmol/kg, 15-ml flush, 7 mL/second right antecubital) the blood signal in the left ventricle (LV) was measured at the bolus peak and compared with the first cycle's fresh magnetization signal. Results:The bolus peak measured 98% Ϯ 4% (mean Ϯ SD, N ϭ 20) of the value before contrast agent arrival. MEASURING MYOCARDIAL PERFUSION requires undistorted arterial input function (AIF) and high signal-to-noise ratio (SNR) myocardial tissue response function measurements. The dual-sequence method (1,4) obtains these measurements in the same cardiac cycle, while the dual-bolus method (2,3) uses separate low-and high-dose first passes for the AIF and myocardial measurements, respectively. The dual-bolus and dual-sequence methods agreed reasonably well in previous in vivo studies (1), and the dual-bolus method has been validated against microspheres as the gold standard (2). ConclusionIn each cardiac cycle, the dual-sequence method (1) acquires a low-resolution image of the left ventricular (LV) blood using a fast (50 msec) sequence with low T1-sensitivity for the AIF, followed by a high-resolution high-T1-sensitivity sequence to acquire images for the myocardial tissue response. The larger voxels of the fast AIF sequence are expected to have more T2* dephasing than those of a typical myocardial perfusion sequence. Larger voxels have more distance over which B0-inhomogeneity may dephase the signal. Conversely, the shorter TE and faster echo sampling of the AIF sequence should reduce T2* effects. It was therefore necessary to test for T2* effects in vivo.The purpose of this work was to examine whether T2* effects in large pixels reduce the accuracy of AIF measurement, which would distort myocardial perfusion measurement by the "dual-sequence" method (1). MATERIALS AND METHODSA Siemens Sonata 1.5T (Numaris 4, VA21) was used with a 12-channel cardiac array coil placed around the patient's chest (six anterior and six posterior elements).In 10 patients referred for assessment of myocardial perfusion, three short-axis myocardial slices were collected on each of 50 cardiac cycles, starting with a breath-hold at end-expiration, imaging the first pass (0.5M Magnevist, 0.1 mmol/kg, and then 15-ml saline flush at 7 mL/second, 18-gauge right antecubital). Adenosine stress (140 g/kg/min) perfusion imaging was performed for clinical examination and the perfusion imaging was repeated at rest after at least 20 minutes. The 50-msec rapid AIF sequence was run at each R-wave w...

Optimization of dual-saturation single bolus acquisition for quantitative cardiac perfusion and myocardial blood flow maps

“…During the same contrast injection different echoes are acquired with the corresponding R2* signal decay. With a contrast dose of 0.1 mmol/kg injected at a rate of 3 ml/s the maximum ΔR2* value was 39Hz, which underestimated AIF by 3.5% for the TE used in the present study (TE = 0.9 ms) and by 2.2% for previously reported TE (TE = 0.58 ms) [ 26 ]. This effect has been compensated for in the contrast conversion procedure by using the estimated relation between the R1 and R2* effects (Figure 4 ) in contrast conversion curves.…”

Myocardial perfusion cardiovascular magnetic resonance: optimized dual sequence and reconstruction for quantification

“…The inherent non-linear response of SR on the AIF was minimized by design of the protocol and post-processing. Earlier dual sequence AIF protocols used centric ordered acquisition to minimize the TS for improved linearity, but this leads to a high pass spatial filtering of the blood pool signal which becomes dependent on gadolinium concentration [10] and creates a dependence on the AIF and how the blood pool is segmented, i.e., the edges of the blood pool will have a longer effective saturation delay. Use of a linear ordering leads to a more homogeneous blood pool image.…”

“…A short readout (64 point) with wide bandwidth (3900 Hz/pixel) and short duration RF pulses (250 μs, time-bandwidth product = 2.0) were used to achieve low T2* losses (TE 1  = 0.76 ms). T2* dephasing loss has been a known concern in estimating AIF and conversion to [Gd] and approaches to this problem have focused either on minimizing the loss by choosing adequately short echo time (TE) [10] or on correcting for T2* loss based on modeling the relationship between T1 and T2* [11, 12]. In this work, the dual sequence approach was modified to incorporate a 2 echo acquisition for measurement of T2* during the bolus passage.…”

Quantitative 3D myocardial perfusion with an efficient arterial input function

“…One benefit of reducing the number of readout samples in the 2D AIF is that a shorter TE could be achieved. A shorter TE for the 2D AIF would reduce or eliminate the need for correction . Because the 2D AIF and 3D acquisitions were interleaved, we were not currently set up to independently set the bandwidth or number of samples for each readout.…”

“…With the efficient AIF measurement, more than 2 echoes could be acquired to model a more complex without increasing scan time. Another possibility is to further reduce TE of the 2D AIF acquisition, which would reduce or eliminate the need for correction …”