SPECT myocardial blood flow quantitation for the detection of angiographic stenoses with cardiac-dedicated CZT SPECT.

PURPOSE: CZT SPECT with the enhanced imaging characteristic facilitates SPECT myocardial blood flow (MBF) quantitation moving toward a clinical utility to uncover myocardial ischemia. The purpose of this study was to investigate the diagnostic performance of stress MBF, myocardial flow reserve (MFR) and myocardial flow capacity (MFC) derived from CZT SPECT in the detection of coronary artery disease (CAD). METHODS: One-hundred and eighty patients underwent two-day rest/adenosine-stress scans for SPECT MBF quantitation. All dynamic SPECT images were reconstructed and corrected with necessary corrections. The one-tissue two-compartment kinetic model was utilized to fit kinetic parameters (K1, k2 and FBV) by numeric optimization and converted to MBF from K1. Rest MBF, stress MBF and MFR in left ventricle and coronary territories were calculated from flow polar maps. MFC was assessed by extents of moderately and severely abnormal flow statuses using an integrated flow diagram. Per-patient and per-vessel analyses were performed to determine cutoff values for the detection of angiographically obstructive and flow-limited CAD. RESULTS: Using the threshold of ≥ 50% stenosis, 149 patients (82.78%) were classified to have obstructive lesions in 355 vessels (65.74%). Using the threshold of ≥ 70% stenosis, 113 patients (62.78%) were classified to have flow-limited lesions in 282 vessels (52.22%). On per-patient analysis, the optimal cutoff values of stress MBF and MFR to detect ≥ 50% stenosis were (1.44 ml/min/g, 1.96) and (1.34 ml/min/g and 1.75) to detect ≥ 70% stenosis. The optimal cutoff values for severely and combined moderately severely abnormal MFC extents were (2.3-2.5%, 23.1%) and (7.5%, 29.4%), respectively. The overall sensitivity of MFC (0.84-0.86, 0.86-0.90) to detect ≥ 50% and ≥ 70% lesions surpassed those of stress MBF (0.78. 0.78) and MFR (0.80, 0.75) (all p < 0.05) with similar specificity (MFC = 0.84-0.90, 0.87-0.91; stress MBF = 0.87, 0.91; MFR = 0.84, 0.89) (all p≥ 0.05). CONCLUSION: The non-invasive SPECT MBF quantitation using CZT SPECT is a reliable method to detect angiographically obstructive and flow-limited CAD. Myocardial flow capacity can outperform with higher diagnostic sensitivity than stress MBF or MFR alone.

Pseudo-spiral sampling and compressed sensing reconstruction provides flexibility of temporal resolution in accelerated aortic 4D flow MRI: A comparison with k-t principal component analysis.

INTRODUCTION: Time-resolved three-dimensional phase contrast MRI (4D flow) of aortic blood flow requires acceleration to reduce scan time. Two established techniques for highly accelerated 4D flow MRI are k-t principal component analysis (k-t PCA) and compressed sensing (CS), which employ either regular or random k-space undersampling. The goal of this study was to gain insights into the quantitative differences between k-t PCA- and CS-derived aortic blood flow, especially for high temporal resolution CS 4D flow MRI. METHODS: The scan protocol consisted of both k-t PCA and CS accelerated 4D flow MRI, as well as a 2D flow reference scan through the ascending aorta acquired in 15 subjects. 4D flow scans were accelerated with factor R = 8. For CS accelerated scans, we used a pseudo-spiral Cartesian sampling scheme, which could additionally be reconstructed at higher temporal resolution, resulting in R = 13. 4D flow data were compared with the 2D flow scan in terms of flow, peak flow and stroke volume. A 3D peak systolic voxel-wise velocity and wall shear stress (WSS) comparison between k-t PCA and CS 4D flow was also performed. RESULTS: The mean difference in flow/peak flow/stroke volume between the 2D flow scan and the 4D flow CS with R = 8 and R = 13 was 4.2%/9.1%/3.0% and 5.3%/7.1%/1.9%, respectively, whereas for k-t PCA with R = 8 the difference was 9.7%/25.8%/10.4%. In the voxel-by-voxel 4D flow comparison we found 13.6% and 3.5% lower velocity and WSS values of k-t PCA compared with CS with R = 8, and 15.9% and 5.5% lower velocity and WSS values of k-t PCA compared with CS with R = 13. CONCLUSION: Pseudo-spiral accelerated 4D flow acquisitions in combination with CS reconstruction provides a flexible choice of temporal resolution. We showed that our proposed strategy achieves better agreement in flow values with 2D reference scans compared with using k-t PCA accelerated acquisitions.

Assessment of cardiac function, blood flow and myocardial tissue relaxation parameters at 0.35 T.

A low field strength (B0) system could increase cardiac MRI availability for patients otherwise contraindicated at higher field. Lower equipment costs could also broaden cardiac MR accessibility. The current study investigated the feasibility of cardiac function with steady-state free precession and flow assessment with phase contrast (PC) cine images at 0.35 T, and evaluated differences in myocardial relaxation times using quantitative T1, T2 and T2* maps by comparison with 1.5 and 3 T results in a small cohort of six healthy volunteers. Signal-to-noise ratio (SNR) differences across systems were characterized with proton density-weighted spin echo phantom data. SNR at 0.35 T was lower by factors of 5.5 and 15.0 compared with the 1.5 and 3 T systems used in this study. All cine images at 0.35 T scored 3 or greater on a five-point image quality scale. Normalized blood-myocardium contrast in cine images, left ventricular volumes (end diastolic volume, end systolic volume) and function (ejection fraction and stroke volume) measures at 0.35 T matched 1.5 and 3 T results. Phase-to-noise ratio in 0.35 T PC images (11.7 ± 1.9) was lower than 1.5 T (18.7 ± 5.2) and 3 T (44.9 ± 16.5). Peak velocity and stroke volume determined from PC images were similar across systems. Myocardial T1 increased (564 ± 13 ms at 0.35 T, 955 ± 19 ms at 1.5 T and 1200 ± 35 ms at 3 T) while T2 (59 ± 4 ms at 0.35 T, 49 ± 3 ms at 1.5 T and 40 ± 2 ms at 3 T) and T2* (42 ± 8 ms at 0.35 T, 33 ± 6 ms at 1.5 T and 24 ± 3 ms at 3 T) decreased with increasing B0. Despite SNR deficits, cardiovascular function, flow assessment and myocardial relaxation parameter mapping is feasible at 0.35 T using standard cardiovascular imaging sequences.

Optimization methods for magnetic resonance imaging gradient waveform design.

The development and implementation of novel MRI pulse sequences remains challenging and laborious. Gradient waveforms are typically designed using a combination of analytical and ad hoc methods to construct each gradient waveform axis independently. This strategy makes coding the pulse sequence complicated, in addition to being time inefficient. As a consequence, nearly all commercial MRI pulse sequences fail to maximize use of the available gradient hardware or efficiently mitigate physiological effects. This results in expensive MRI systems that underperform relative to their inherent hardware capabilities. To address this problem, a software solution is proposed that incorporates numerical optimization methods into MRI pulse sequence programming. Examples are shown for rotational variant vs. invariant waveform designs, acceleration nulled velocity encoding gradients, and mitigation of peripheral nerve stimulation for diffusion encoding. The application of optimization methods to MRI pulse sequence design incorporates gradient hardware limits and the prescribed MRI protocol parameters (e.g. field-of-view, resolution, gradient moments, and/or b-value) to simultaneously construct time-optimal gradient waveforms. In many cases, the resulting constrained gradient waveform design problem is convex and can be solved on-the-fly on the MRI scanner. The result is a set of multi-axis time-optimal gradient waveforms that satisfy the design constraints, thereby increasing SNR-efficiency. These optimization methods can also be used to mitigate imaging artifacts (e.g. eddy currents) or account for peripheral nerve stimulation. The result of the optimization method is to enable easier pulse sequence gradient waveform design and permit on-the-fly implementation for a range of MRI pulse sequences.

Simplified quantification of 13N-ammonia PET myocardial blood flow: A comparative study with the standard compartment model to facilitate clinical use.

BACKGROUND: Short imaging protocol to quantify myocardial blood flow (MBF) and myocardial flow reserve (MFR) may enhance the clinical application of 13N-ammonia cardiac PET. We assessed the flow quantitation of 13N-ammonia PET implementing simple retention model and two-compartment model. METHODS: Fourteen healthy volunteers (HVT) and twenty-three clinical patients received 13N-ammonia PET/CT. The simple retention model used the first 7-minute image to quantify MBF. Global and regional MBF and MFR of the two models were compared. RESULTS: Global and regional MBF and MFR of these two models were highly correlated with mildly inferior correlation in RCA territory (global R2: rest MBF = 0.79, stress MBF = 0.65, MFR = 0.77; regional R2: rest MBF ≥ 0.72, stress MBF ≥ 0.52, MFR ≥ 0.68). There were significant differences for MFR (4.04 ± 0.72, 3.66 ± 0.48, p = .02) and rest MBF (0.69 ± 0.12, 0.78 ± 0.12, p = .02) between the two models in the HVT group. CONCLUSIONS: 13N-ammonia global and regional MBF and MFR from the simple retention model demonstrate strong correlations with that from the two-compartment model. Significant differences of MFR and rest MBF are noted in the HVT group, with a proposed normal reference value for the 13N-ammonia short simple retention protocol.

Myocardial blood flow quantitation in patients with congestive heart failure: head-to-head comparison between rapid-rotating gantry SPECT and CZT SPECT.

PURPOSE: Recently, the feasibility of myocardial blood flow (MBF) quantitation using rapid-rotating gantry (RRG) and cadmium-zinc-telluride (CZT) SPECT cameras has been demonstrated. We compared MBF quantitation using these two camera systems. METHODS: Twenty patients with congestive heart failure (CHF) and 20 patients without CHF (non-CHF) were included. On two consecutive days, dynamic SPECT imaging was performed after a bolus injection of 20 mCi of 99mTc-Sestamibi (MIBI) with RRG-SPECT and list-mode acquisition with CZT-SPECT. All dynamic SPECT images were reconstructed with full physical corrections, corrections for ventricular spillover and partial volume effect, using one-tissue kinetic modeling. Resting MBF converted from K1 was then corrected for MIBI extraction fraction and adjusted for rate-pressure product. RESULTS: In both patient groups, there was no significant difference between resting MBF values measured with RRG-SPECT and CZT-SPECT systems (P = 0.06, P = 0.2 respectively). For CHF patients, linear regression (LR) was y(RRG) = 1.0412x (CZT) (r = 0.97) with a small systemic difference (Δ = 0.03 mL·min-1·g-1, 95% CI - 0.11 to 0.20) by Bland-Altman analysis. For non-CHF patients, LR was y(RRG) = 1.025x (CZT) (r = 0.89) with also small systemic difference (ΔT= 0.02 mL·min-1·g-1, 95% CI - 0.14 to 0.19) in BA analysis. CONCLUSION: Physical corrections along with other image corrections can provide comparable MBF quantitations in both CHF and non-CHF patients, regardless of the type of SPECT systems used.

SPECT myocardial blood flow quantitation toward clinical use: a comparative study with 13N-Ammonia PET myocardial blood flow quantitation.

OBJECTIVES: The aim of this study was to evaluate the accuracy of myocardial blood flow (MBF) quantitation of 99mTc-Sestamibi (MIBI) single photon emission computed tomography (SPECT) compared with 13N-Ammonia (NH3) position emission tomography (PET) on the same cohorts. BACKGROUND: Recent advances of SPECT technologies have been applied to develop MBF quantitation as a promising tool to diagnose coronary artery disease (CAD) for areas where PET MBF quantitation is not available. However, whether the SPECT approach can achieve the same level of accuracy as the PET approach for clinical use still needs further investigations. METHODS: Twelve healthy volunteers (HVT) and 16 clinical patients with CAD received both MIBI SPECT and NH3 PET flow scans. Dynamic SPECT images acquired with high temporary resolution were fully corrected for physical factors and processed to quantify K1 using the standard compartmental modeling. Human MIBI tracer extraction fraction (EF) was determined by comparing MIBI K1 and NH3 flow on the HVT group and then used to convert flow values from K1 for all subjects. MIBI and NH3 flow values were systematically compared to validate the SPECT approach. RESULTS: The human MIBI EF was determined as [1.0-0.816*exp(-0.267/MBF)]. Global and regional MBF and myocardial flow reserve (MFR) of MIBI SPECT and NH3 PET were highly correlated for all subjects (global R2: MBF = 0.92, MFR = 0.78; regional R2: MBF ≥ 0.88, MFR ≥ 0.71). No significant differences for rest flow, stress flow, and MFR between these two approaches were observed (All p ≥ 0.088). Bland-Altman plots overall revealed small bias between MIBI SPECT and NH3 PET (global: ΔMBF = -0.03Lml/min/g, ΔMFR = 0.07; regional: ΔMBF = -0.07 - 0.06 , ΔMFR = -0.02 - 0.22). CONCLUSIONS: Quantitation with SPECT technologies can be accurate to measure myocardial blood flow as PET quantitation while comprehensive imaging factors of SPECT to derive the variability between these two approaches were fully addressed and corrected.

Avoiding full corrections in dynamic SPECT images impacts the performance of SPECT myocardial blood flow quantitation.

INTRODUCTION: This study investigated the performance of SPECT myocardial blood flow (MBF) quantitation lacking full physical corrections (All Corr) in dynamic SPECT (DySPECT) images. METHODS: Eleven healthy normal volunteers (HVT) and twenty-four patients with angiography-documented CAD were assessed. All Corr in 99mTc-sestamibi DySPECT encompassed noise reduction (NR), resolution recovery (RR), and corrections for scatter (SC) and attenuation (AC), otherwise no correction (NC) or only partial corrections. The performance was evaluated by quality index (R 2) and blood-pool spillover index (FBV) in kinetic modeling, and by rest flow (RMBF) and stress flow (SMBF) compared with those of All Corr. RESULTS: In HVT group, NC diminished 2-fold flow uniformity with the most degraded quality (15%-18% reduced R 2) and elevated spillover effect (45%-50% increased FBV). Consistently higher RMBF and SMBF were discovered in both groups (HVT 1.54/2.31 higher; CAD 1.60/1.72; all P < .0001). Bland-Altman analysis revealed positive flow bias (HVT 0.9-2.6 mL/min/g; CAD 0.7-1.3) with wide ranges of 95% CI of agreement (HVT NC -1.9-7.1; NR -0.4-4.4; NR + SC -1.1-4.3; NR + SC + RR -0.7-2.5) (CAD NC -1.2-3.8; NR -1.0-2.8; NR + SC -1.0-2.5; NR + SC + RR -1.1-2.6). CONCLUSIONS: Uncorrected physical interference in DySPECT images can extensively impact the performance of MBF quantitation. Full physical corrections should be considered to warrant this tool for clinical utilization.

Inter- and intra-rater reliability of blood and cerebrospinal fluid flow quantification by phase-contrast MRI.

PURPOSE: To evaluate the intra- and inter-rater reliability of the quantification of blood and CSF flow rates by phase contrast MRI. MATERIALS AND METHODS: Blood and CSF flows in the upper cervical region were imaged with velocity-encoded cine-phase contrast using 3T scanners from different manufacturers at two centers. Data of 6 subjects scanned in center A and of 5 subjects in center B were analyzed by six readers at two levels of training. Each data set was analyzed three times in a randomized order for a total of 33 data sets. Intra-class correlation coefficients (ICC) were calculated for the primary measurements of areas and flow rates through the main cervical arteries, veins and the CSF space, and for secondary parameters derived from the individual flow rates. RESULTS: ICC ranged from 0.80 to 0.96 for the lumen area and from 0.97 to 0.99 for the volumetric flow rate. The ICC for the derived secondary measures ranged from 0.85 to 0.99. Differences due to operator level of training were not statistically significant. CONCLUSION: High intra- and inter-rater reliability of volumetric flow rate measurements is currently achievable across manufacturers and users' skill levels with a pulsatility based automated lumen segmentation.

A method to measure the extent of myocardial ischemia and steal with SPECT myocardial blood flow quantitation.

OBJECTIVE: We introduced a method to measure the extent of myocardial ischemia and steal with SPECT MBF quantitation. METHODS: Eighty-seven patients who received rest/Dipyridamole-stress 99mTc-Sestamibi (MIBI) dynamic SPECT scans and coronary angiography were included. Dynamic SPECT images were reconstructed with full physical corrections. The one-tissue kinetic model was utilized to quantify K1 and further converted to MBF with required corrections. Rest MBF, stress MBF and myocardial flow reserve (MFR) were converted to a flow status polar map by a flow diagram. Extents of 7 flow statuses were verified their cutoff points for detecting stenoses. The diagnostic performance (DP) was compared to that of MFR. RESULTS: Cutoff point of the extent to detect ≥ 50% stenosis was 3.01% for ischemia-steal status and 20.3% for the combined status of ischemia-steal and moderate. Using these criteria, sensitivity, specificity and accuracy to detect ≥ 50% stenosis were (80%, 75%, 79%) and (86%, 68%, 80%) for ≥ 70% stenosis. The DP was superior to that of MFR < 2.0 criterion (≥ 50%: 70%, 63%, 69%; ≥ 70%: 73%, 61%, 69%) (all p < 0.015). CONCLUSION: SPECT MBF quantitation integrated with the flow diagram can measure the extent of myocardial ischemia and steal which appeared more accurate to detect angiographic stenoses than the single MFR parameter.