Feasibility of detecting cardiac torsion in myocardial perfusion gated SPECT data

Motion estimation and correction in SPECT, PET and CT

Patient motion impacts single photon emission computed tomography (SPECT), positron emission tomography (PET) and X-ray computed tomography (CT) by giving rise to projection data inconsistencies that can manifest as reconstruction artifacts, thereby degrading image quality and compromising accurate image interpretation and quantification. Methods to estimate and correct for patient motion in SPECT, PET and CT have attracted considerable research effort over several decades. The aims of this effort have been two-fold: to estimate relevant motion fields characterizing the various forms of voluntary and involuntary motion; and to apply these motion fields within a modified reconstruction framework to obtain motion-corrected images. The aims of this review are to outline the motion problem in medical imaging and to critically review published methods for estimating and correcting for the relevant motion fields in clinical and preclinical SPECT, PET and CT. Despite many similarities in how motion is handled between these modalities, utility and applications vary based on differences in temporal and spatial resolution. Technical feasibility has been demonstrated in each modality for both rigid and non-rigid motion, but clinical feasibility remains an important target. There is considerable scope for further developments in motion estimation and correction, and particularly in data-driven methods that will aid clinical utility. State-of-the-art machine learning methods may have a unique role to play in this context.

Robust model-based quantification of global ventricular torsion from spatially sparse three-dimensional time series data by orthogonal distance regression: evaluation in a canine animal model under different pacing regimes

BACKGROUND

Quantification of global ventricular rotational deformation, expressed as twist or torsion, and its dynamic changes is important in understanding the pathophysiology of heart disease and its therapy. Various techniques, such as sonomicrometry, allow tracking of specific sites within the myocardium. Quantification of twist from such data requires a longitudinal reference axis of rotation. Current methods require specific positioning and numbers of myocardial markers and assumptions about temporal positional evolution that may be violated during dyssynchronous contraction.

METHODS

We present a new method to assess myocardial twist that makes minimal fully explicit assumptions while removing extraneous assumptions, by performing a least squares orthogonal distance regression of all position data on an ellipsoidal ventricular model. Rotational deformation is quantified in terms of the ellipsoid's internal coordinate system, allowing intuitive visualization.

RESULTS

We tested this method on a set of sparse, noisy sonomicrometric crystal data in dogs under different pacing regimes to model dyssynchrony and cardiac resynchronization. We found that this method yielded robust and plausible data. This technique is also fully automated while identifying when data may be insufficient for reliable quantification of rotational deformation.

CONCLUSION

This approach may allow future analysis of myocardial contraction with less tracking sites and relaxed positioning requirements while identifying situations where data are insufficient for reliable quantification of rotational deformation.

Ventricular dyssynchrony assessed by gated myocardial perfusion SPECT using a geometrical approach: a feasibility study

PURPOSE

Left ventricular dyssynchrony may predict response to cardiac resynchronization therapy and may well predict adverse cardiac events. Recently, a geometrical approach for dyssynchrony analysis of myocardial perfusion scintigraphy (MPS) was introduced. In this study the feasibility of this geometrical method to detect dyssynchrony was assessed in a population with a normal MPS and in patients with documented ventricular dyssynchrony.

METHODS

For the normal population 80 patients (40 men and 40 women) with normal perfusion (summed stress score ≤2 and summed rest score ≤2) and function (left ventricular ejection fraction 55-80%) on MPS were selected; 24 heart failure patients with proven dyssynchrony on MRI were selected for comparison. All patients underwent a 2-day stress/rest MPS protocol. Perfusion, function and dyssynchrony parameters were obtained by the Corridor4DM software package (Version 6.1).

RESULTS

For the normal population time to peak motion was 42.8 ± 5.1% RR cycle, SD of time to peak motion was 3.5 ± 1.4% RR cycle and bandwidth was 18.2 ± 6.0% RR cycle. No significant gender-related differences or differences between rest and post-stress acquisition were found for the dyssynchrony parameters. Discrepancies between the normal and abnormal populations were most profound for the mean wall motion (p value <0.001), SD of time to peak motion (p value <0.001) and bandwidth (p value <0.001).

CONCLUSION

It is feasible to quantify ventricular dyssynchrony in MPS using the geometrical approach as implemented by Corridor4DM.

Quantitative study of cardiac motion estimation and abnormality classification in emission computed tomography

Quantitative description of cardiac motion is desirable to assist in detecting myocardial abnormalities from gated myocardial perfusion (GMP) emission computed tomography (ECT) images. While "optical flow" type of cardiac motion estimation (ME) techniques have been developed in the past, there has been no quantitative evaluation of their performance. Moreover, no investigation has been performed in terms of applying an ME technique to quantify cardiac motion abnormalities. Using the four-dimensional NCAT beating heart phantom with known built-in motion, the current work aimed at addressing the aforementioned two issues. A three-dimensional cardiac ME technique was developed to search for a motion vector field (MVF) that establishes voxel-by-voxel correspondence between two GMP ECT images. The weighted myocardial strain energy served as the constraint in the process to minimize the difference between one intensity image and the MVF warped other. We studied the convergence of the ME technique using different initial estimates and cost functions. The dependence of estimated MVF on the initialization was attributed to the tangential motion that is undetectable while not suppressed by the strain energy constraint. We optimized the strain energy constraint weighting using noise-free phantom images and noisy reconstructed images, the former against the known MVF and the later in the task of regional motion classification. While the results from the above two studies well coincide with each other, we also demonstrated that upon appropriate optimization the ME method has the capability of serving as a computer motion observer in separating simulated noisy reconstructed GMP SPECT images corresponding to hearts with and without regional motion abnormalities.

Helical heart on ECG gated 99mTc-tetrofosmin SPECT: counterclockwise rotation of lesion axis on wall thickening polar map as compared with that on perfusion polar map in patients with coronary artery disease

OBJECTIVE

The location of a myocardial lesion on a wall thickening polar map often does not coincide with the location of the lesion on a perfusion polar map, especially when the myocardial lesion is located at the mid cardiac region. The purpose of this study was to determine the frequency and extent of discrepancy in the location of the lesion between perfusion and wall thickening polar maps on gated single photon emission computed tomography (SPECT) using lesion axis angle (LAA).

METHODS

One hundred and forty-seven consecutive patients (male : female = 80 : 67, age range: 41-96 years) who underwent myocardial gated (99m)Tc-tetrofosmin SPECT on the suspicion of myocardial ischemia or infarct between September 2003 and September 2008 and showed both reduced myocardial perfusion and wall thickening on gated SPECT at mid cardiac region were reviewed. LAA, which is the angle between the lesion axis on perfusion and wall thickening polar maps, was measured for the patients who showed a discrepancy in lesion axis between the two polar maps. LAA was said to have a positive value when the lesion axis of the wall thickening polar map showed a counterclockwise angular rotation as compared with that of a perfusion polar map. The patients with LAA of less than 10 degrees were considered as having no lesion axis discrepancy between perfusion and wall thickening polar maps. LAA was correlated with left ventricular ejection fraction (LVEF) on gated SPECT using Pearson's correlation. Furthermore, two groups, one with LAA of >or=10 degrees and the other with LAA less than 10 degrees were correlated with dichotomous groups with >or=50% and less than 50% LVEF, using the chi(2) test. Then, 35 patients with acute coronary syndrome (ACS group) were analyzed separately for correlation between LAA and LVEF.

RESULTS

The mean +/- SD of LAA was 44.31+/-30.77 degrees (range: 0-145 degrees ). LAA was 0-10 degrees in 25 patients, 11-30 degrees in 24 patients, 31-60 degrees in 58 patients, 61-90 degrees in 30 patients, and >90 degrees in 10 patients. In addition, the lesion axis of the wall thickening polar map as compared with that of the perfusion polar map was rotated in the counterclockwise direction in 122 patients and not rotated in 25 patients. LVEF on gated SPECT showed positive correlation with LAA (P = 0.000147). In addition, there was statistically significant correlation (P = 0.001) when the two groups with LAA of >or=10 degrees and less than 10 degrees , respectively, were correlated with the groups of >or=50% and less than 50% LVEF. For the ACS group, the mean +/- SD of LAA was 45.88+/-30.30 degrees (range: 0-135 degrees ) and LVEF showed positive correlation with LAA (P = 0.0001). There was no significant statistical difference concerning LAA and LVEF between ACS group and non-ACS group (P = 0.725 and P = 0.473, respectively).

CONCLUSION

In most of our patients with coronary artery disease, the lesion axis of reduced wall thickening was rotated in the counterclockwise direction as compared with that of reduced perfusion on SPECT polar maps, especially when the myocardial lesion was at mid cardiac region. The LAA decreased as the LVEF decreased. This might be related to spatiotemporal distortion of myocardial contraction mentioned in the helical heart concept.

New options in noninvasive assessment of left ventricular torsion

The complex, intricate 3D pattern of ventricular torsion has both fascinated and perplexed scientists for centuries. The identity of the underlying anatomic myocardial unit responsible for this pattern of contraction continues to be an arena of debate. While the complicated wringing motions involved in torsion are difficult to quantify, several techniques have been demonstrated to be effective in the noninvasive assessment of left ventricular (LV) torsion. Magnetic resonance tissue-tagging with dynamic MRI is the gold standard for the noninvasive quantitative evaluation of torsion with high spatial and temporal resolution. However, this is a technically involved and potentially time-consuming process. Echocardiography is another alternative noninvasive method. Both tissue Doppler imaging and speckle-tracking imaging have been shown to be sufficiently accurate and reliable alternatives to MRI in the noninvasive assessment of LV torsion. While the potential applications of these techniques to assess LV torsion appears boundless, further studies are needed to validate measures of LV torsion by the additional, but most important, test of demonstrating its clinical utility as a predictor of prognosis.

Sensitivity, specificity and accuracy of stress SPECT myocardial perfusion imaging for detection of coronary artery disease in the distribution of first-order branch vessels, using an anatomical matching of angiographic and perfusion data

We sought to investigate the utility of stress single-photon emission computed tomography (SPECT) myocardial perfusion imaging (MPI) for the identification of coronary artery disease (CAD) in the distribution of first-order branch vessels. We evaluated 135 consecutive patients with coronary angiography and stress SPECT MPI. We anatomically matched angiography and SPECT to assess the sensitivity, specificity and accuracy of SPECT MPI for the detection of CAD in the distribution of first-order branches. Subgroup analysis for stress test performance and previous coronary artery bypass grafting (CABG) was also performed. The sensitivity, specificity and accuracy of stress SPECT MPI for the detection of CAD in the distribution of first-order branch vessels were all 67%. For isolated branch vessel CAD, stress SPECT MPI had a sensitivity of 44%. In patients without CABG, the sensitivity, specificity and accuracy for the detection of CAD in the distribution of first-order branch vessels were 71%, 67% and 68%, compared with 60%, 67% and 64% for patients with CABG. The sensitivity for isolated branch vessel CAD was 50% for patients without CABG, but only 29% for patients with CABG. The sensitivity and specificity for CAD in the distribution of branch vessels were similar for all patients for all stress test modalities and heart rate response (sensitivity, 64-69%; specificity, 61-69%). Stress SPECT MPI offers intermediate sensitivity, specificity and accuracy for the detection of CAD in the distribution of first-order coronary artery branch vessels. However, for isolated branch vessel CAD, stress SPECT has a lower sensitivity, particularly in patients with previous CABG.