The problem of radiotracer abdominal activity in myocardial perfusion imaging studies

Effect of proton pump inhibitors on Rubidium-82 gastric uptake using positron emission tomography myocardial perfusion imaging

BACKGROUND

Rb-82 positron emission tomography (PET) myocardial perfusion imaging (MPI) is a robust tool for the evaluation of coronary artery disease (CAD). However, gastric uptake and spillover can be seen in 10% of Rb-82 PET MPI studies, commonly affecting the inferior wall, and can preclude the accurate identification of myocardial ischemia. We sought to understand the relationship between Rb-82 gastric uptake and the use of proton pump inhibitors (PPI).

METHODS

600 consecutive patients who presented for a clinically indicated Rb-82 PET MPI study were prospectively enrolled. In addition to the clinical history, PPI use was ascertained (medication, dose, frequency and duration of use, and time of last dose). Patients were categorized as PPI and non-PPI users. Rb-82 uptake in the gastrium, myocardium, and liver were measured at rest. Absolute uptake values and gastric:hepatic ratios were compared in PPI and non-PPI users.

RESULT

Of 600 enrolled patients, 181 (30.2%) patients were using PPI. The gastric Rb-82 uptake in PPI users was 23% higher than non-PPI users (146 ± 52 kBq/cc vs 119 ± 40 kBq/cc, respectively; P < 0.001). The resting gastric:hepatic Rb-82 uptake ratio was also 23% higher in PPI vs non-PPI users (2.7 ± 1.0 vs 2.2 ± 0.8, respectively; P < 0.001).

CONCLUSION

The gastric uptake of Rb-82 appears to be greater in patients actively using PPI and may identify a group who might be at greater risk of non-diagnostic Rb-82 PET MPI.

A Comparison of Iterative Reconstruction and Prone Imaging in Reducing the Inferior Wall Attenuation in Tc-99m Sestamibi Myocardial Perfusion SPECT

Objective:

Prone positioning, iterative reconstruction (IR-OSEM) and electrocardiography (ECG) gating have been demonstrated to improve the specificity of myocardial perfusion SPECT (MPS) in the diagnosis of coronary artery disease.

Methods:

The gated supine and prone MPS images of 45 patients were reconstructed with both IR-OSEM [supine (SIR) and prone (PIR)] FBPs [supine (SFBP), prone (PFBP)] for comparison. Perfusion, wall motion (WM) and wall thickening were also interpreted semi-quantitatively. Two groups were generated as those with normal or abnormal findings. Segmental myocardial tracer uptake values were noted from four of the reconstructed images from 17 segment model of bullseye.

Results:

The difference between mean values and the standard deviations of the % tracer uptakes of inferior wall segments were statistically significant in all images. The normalcy rates were highest in PIR images, followed by PFBP and SIR images. The number of patients with any perfusion abnormality were 42, 12, 32, and 6, in SFBP, PFBP, SIR and PIR images, respectively. The six patients with perfusion abnormality in PIR images were re-evaluated with rest images and were diagnosed with a fixed perfusion defect. There was positive correlation between WM and either PFBP or PIR images. Sixteen patients’ WM were evaluated as abnormal while only 6 patients’ perfusions were abnormal in PIR.

Conclusion:

Prone imaging in addition to a supine perfusion SPECT improves imaging quality of the inferior wall, especially when reconstructed with iterative methods. If prone imaging can not be performed, ECG-gating can also be used as a beneficial method.

Increased Gastric Activity on Myocardial Perfusion Imaging

We anecdotally observed an increased accumulation of (99m)Tc-tetrofosmin in the stomach of myocardial perfusion patients when their uptake phase coincided with preparation of hamburgers in an adjacent room for gastric emptying studies on other patients. The potential for a scent-stimulated alteration of gastric biodistribution required further investigation.

METHODS

An experimental group and a control group were enrolled (20 patients per group). The experimental group could smell food being prepared during the uptake phase. Stomach, heart, and background regions were drawn in multiple projections, and the resulting data were evaluated.

RESULTS

The experimental and control groups did not significantly differ in stomach counts per pixel, background-corrected counts per pixel, or heart-to-stomach ratio. Further analysis of the data revealed that women had a significantly higher increase in stomach counts (P = 0.022) and background-corrected stomach counts (P = 0.018) than men.

CONCLUSION

Women had a greater increase in gastric (99m)Tc-tetrofosmin activity than men during the radiopharmaceutical uptake phase, but there was no causal relationship between an increase in activity and olfactory stimulation from the cooking of food.

Detection and severity classification of extracardiac interference in ⁸²Rb PET myocardial perfusion imaging

PURPOSE

Myocardial perfusion imaging (MPI) is used for diagnosis and prognosis of coronary artery disease. When MPI studies are performed with positron emission tomography (PET) and the radioactive tracer rubidium-82 chloride ((82)Rb), a small but non-negligible fraction of studies (∼10%) suffer from extracardiac interference: high levels of tracer uptake in structures adjacent to the heart which mask the true cardiac tracer uptake. At present, there are no clinically available options for automated detection or correction of this problem. This work presents an algorithm that detects and classifies the severity of extracardiac interference in (82)Rb PET MPI images and reports the accuracy and failure rate of the method.

METHODS

A set of 200 (82)Rb PET MPI images were reviewed by a trained nuclear cardiologist and interference severity reported on a four-class scale, from absent to severe. An automated algorithm was developed that compares uptake at the external border of the myocardium to three thresholds, separating the four interference severity classes. A minimum area of interference was required, and the search region was limited to that facing the stomach wall and spleen. Maximizing concordance (Cohen's Kappa) and minimizing failure rate for the set of 200 clinician-read images were used to find the optimal population-based constants defining search limit and minimum area parameters and the thresholds for the algorithm. Tenfold stratified cross-validation was used to find optimal thresholds and report accuracy measures (sensitivity, specificity, and Kappa).

RESULTS

The algorithm was capable of detecting interference with a mean [95% confidence interval] sensitivity/specificity/Kappa of 0.97 [0.94, 1.00]/0.82 [0.66, 0.98]/0.79 [0.65, 0.92], and a failure rate of 1.0% ± 0.2%. The four-class overall Kappa was 0.72 [0.64, 0.81]. Separation of mild versus moderate-or-greater interference was performed with good accuracy (sensitivity/specificity/Kappa = 0.92 [0.86, 0.99]/0.86 [0.71, 1.00]/0.78 [0.64, 0.92]), while separation of moderate versus severe interference severity classes showed reduced sensitivity/Kappa but little change in specificity (sensitivity/specificity/Kappa = 0.83 [0.77, 0.88]/0.82 [0.77, 0.88]/0.65 [0.60, 0.70]). Specificity was greater than sensitivity for all interference classes. Algorithm execution time was <1 min.

CONCLUSIONS

The algorithm produced here has a low failure rate and high accuracy for detection of extracardiac interference in (82)Rb PET MPI scans. It provides a fast, reliable, automated method for assessing severity of extracardiac interference.

Evaluation of variability of phase indices of the left ventricle in the course of time

OBJECTIVE

Since the effect of time on phase indices is still unclear, the aim of the study was to evaluate the variability of phase indices of the left ventricle which were derived from stress and rest single-photon emission computed tomography (SPECT) imaging acquired at early and late times.

METHODS

One hundred twenty-one patients (72 men, 49 women) were included into the study. All stress and rest gated myocardial perfusion imaging (gMPI) acquisitions were acquired at two different time points as early in 15 ± 5 min and late in 45 ± 5 min. The peak of the phase histogram (PP), the standard deviation of the phase distribution (SDPH), the width of the band (BPH), and the symmetry (histogram skewness, HS) and peakedness of the phase histogram (histogram kurtosis, HK) which are the parameters for assessing left ventricular systolic dyssynchrony were calculated in all stress and rest SPECT images acquired twice.

RESULTS

The phase indices derived from the late rest scans were smaller than those of the early rest scans but, the differences were not significant. When considering the comparisons of phase indices derived from two different time points after stress, PP showed a tendency to decrease (from 160.8 ± 18.3 to 152.5 ± 17.3; p < 0.001) over time but SDPH (from 20.2 ± 10.6 to 22.4 ± 12.2; p = 0.018) and BPH (from 61.5 ± 36.0 to 66.3 ± 37.3; p = 0.045) tended to increase over time. When the post-stress and the resting dyssynchrony parameters derived at two different time points were compared to each other; PP decreased at early and late times approximately 12 and 9 %, respectively, SDPH increased at early and late times approximately 28.5 and 14 %, respectively, and BPH increased at early and late times approximately 23 and 12 %, respectively.

CONCLUSIONS

In resting conditions, phase indices of the left ventricle, and therefore, the phase histogram tend to remain constant over time but, in conditions after exercise, the phase histogram tend to be long and narrow due to changes in phase indices and it shows tendency to return to resting conditions in time. Therefore, it appears that postexercise acquisition times should be standardized if we want to compare the phase indices results of the studies in the literature.

The impact of adenosine pharmacologic stress combined with low-level exercise in patients undergoing myocardial perfusion imaging (BIWAKO adenosine-Ex trial)

BACKGROUND

The combination of adenosine infusion with low-level exercise has become a common approach for inducing stress during stress myocardial perfusion imaging (MPI). We investigated stress MPI performed by combined low-level exercise and adenosine infusion. This combined protocol can decrease adverse reactions and reduce the effect of scattered rays from the liver.

METHODS AND RESULTS

Subjects were clinically referred for a 53-min rest-stress Tc-99m Sestamibi MPI procedure using BIWAKO PROTOCOL. Ninety-eight patients (44.5%) underwent adenosine infusion with ergometer exercise testing and 122 patients (55.5%) underwent adenosine infusion without exercise testing. We evaluated the liver/heart (L/H) uptake ratio, background activity in the upper mediastinum, and adverse reactions.

RESULTS

The L/H ratio and background activity were lower in the adenosine-exercise group than in the adenosine-non-exercise group (1.8 ± 0.54 vs. 2.1 ± 0.62, P < 0.0056; 43.1 ± 12.2 vs. 61.5 ± 15.4, P < 0.0001). The adenosine-exercise group had fewer adverse reactions than the adenosine-non-exercise group (11.2 vs. 19.7%). All of the adverse reactions were minor, with the exception of severe back pain in one case. The incidence of adverse reactions in our study was lower than that in previous studies for unknown reason.

CONCLUSION

Adenosine infusion in combination with low-level exercise seems to result in higher-quality images and fewer adverse reactions than adenosine infusion without exercise. The combined protocol decreases adverse reactions and improves the quality of myocardial perfusion images by decreasing background activity.