Patient-tailored risk assessment of obstructive coronary artery disease using Rubidium-82 PET-based myocardial flow quantification with visual interpretation

INTRODUCTION

Our aim was to estimate the probability of obstructive CAD (oCAD) for an individual patient as a function of the myocardial flow reserve (MFR) measured with Rubidium-82 (Rb-82) PET in patients with a visually normal or abnormal scan.

MATERIALS AND METHODS

We included 1519 consecutive patients without a prior history of CAD referred for rest-stress Rb-82 PET/CT. All images were visually assessed by two experts and classified as normal or abnormal. We estimated the probability of oCAD for visually normal scans and scans with small (5%-10%) or larger defects (> 10%) as function of MFR. The primary endpoint was oCAD on invasive coronary angiography, when available.

RESULTS

1259 scans were classified as normal, 136 with a small defect and 136 with a larger defect. For the normal scans, the probability of oCAD increased exponentially from 1% to 10% when segmental MFR decreased from 2.1 to 1.3. For scans with small defects, the probability increased from 13% to 40% and for larger defects from 45% to > 70% when segmental MFR decreased from 2.1 to 0.7.

CONCLUSION

Patients with > 10% risk of oCAD can be distinguished from patients with < 10% risk based on visual PET interpretation only. However, there is a strong dependence of MFR on patient's individual risk of oCAD. Hence, combining both visual interpretation and MFR results in a better individual risk assessment which may impact treatment strategy.

Machine learning based model to diagnose obstructive coronary artery disease using calcium scoring, PET imaging, and clinical data

INTRODUCTION

Accurate risk stratification in patients with suspected stable coronary artery disease is essential for choosing an appropriate treatment strategy. Our aim was to develop and validate a machine learning (ML) based model to diagnose obstructive CAD (oCAD).

METHOD

We retrospectively have included 1007 patients without a prior history of CAD who underwent CT-based calcium scoring (CACS) and a Rubidium-82 PET scan. The entire dataset was split 4:1 into a training and test dataset. An ML model was developed on the training set using fivefold stratified cross-validation. The test dataset was used to compare the performance of expert readers to the model. The primary endpoint was oCAD on invasive coronary angiography (ICA).

RESULTS

ROC curve analysis showed an AUC of 0.92 (95% CI 0.90-0.94) for the training dataset and 0.89 (95% CI 0.84-0.93) for the test dataset. The ML model showed no significant differences as compared to the expert readers (p ≥ 0.03) in accuracy (89% vs. 88%), sensitivity (68% vs. 69%), and specificity (92% vs. 90%).

CONCLUSION

The ML model resulted in a similar diagnostic performance as compared to expert readers, and may be deployed as a risk stratification tool for obstructive CAD. This study showed that utilization of ML is promising in the diagnosis of obstructive CAD.

Semi-quantitative assessment of ischemia with rubidium-82 PET myocardial perfusion imaging

PURPOSE

Semi-quantitative scores can be used as an adjunct to visual assessment in rubidium-82 positron emission tomography (82Rb PET). The semi-quantitative cut-off values used in 82Rb PET are derived from single-photon emission computed tomography (SPECT). It is unknown whether these cut-off values can be extrapolated to 82Rb PET. We compared the semi-quantitative with the visual assessment of ischemia and determined which summed difference score (SDS) score predicts ischemia best.

METHODS

We included 108 patients who underwent 82Rb PET imaging and performed visual and semi-quantitative assessment. A scan with a SDS ≥ 2 and a summed stress score (SSS) ≥ 4 was considered to demonstrate ischemia. We compared the semi-quantitative with the visual assessment.

RESULTS

41 (38%) Normal scans, and 67 (62%) scans with ischemia and/or an irreversible defect were included. The semi-quantitative assessment showed ischemia more often than the visual assessment (51% vs 29%, P < .001). Patients with a low or intermediate pre-test probability of coronary artery disease (CAD) and a SDS < 4 did not demonstrate ischemia by visual assessment.

CONCLUSION

Semi-quantitative assessment in 82Rb PET imaging clearly demonstrates the presence of ischemia. Ischemia is unlikely in patients with low and intermediate pre-test probability of CAD and a SDS < 4.

Semi-quantitative assessment of ischemia with rubidium-82 PET myocardial perfusion imaging

PURPOSE

Semi-quantitative scores can be used as an adjunct to visual assessment in rubidium-82 positron emission tomography (⁸²Rb PET). The semi-quantitative cut-off values used in ⁸²Rb PET are derived from single-photon emission computed tomography (SPECT). It is unknown whether these cut-off values can be extrapolated to ⁸²Rb PET. We compared the semi-quantitative with the visual assessment of ischemia and determined which summed difference score (SDS) score predicts ischemia best.

METHODS

We included 108 patients who underwent ⁸²Rb PET imaging and performed visual and semi-quantitative assessment. A scan with a SDS ≥ 2 and a summed stress score (SSS) ≥ 4 was considered to demonstrate ischemia. We compared the semi-quantitative with the visual assessment.

RESULTS

41 (38%) Normal scans, and 67 (62%) scans with ischemia and/or an irreversible defect were included. The semi-quantitative assessment showed ischemia more often than the visual assessment (51% vs 29%, P < .001). Patients with a low or intermediate pre-test probability of coronary artery disease (CAD) and a SDS < 4 did not demonstrate ischemia by visual assessment.

CONCLUSION

Semi-quantitative assessment in ⁸²Rb PET imaging clearly demonstrates the presence of ischemia. Ischemia is unlikely in patients with low and intermediate pre-test probability of CAD and a SDS < 4.

Long-standing persistent atrial fibrillation with low coronary flow reserve is associated with unnecessary coronary angiography

Background/Introduction

Atrial fibrillation (AF) is associated with an increased risk of myocardial infarction. Myocardial perfusion imaging (MPI) is well-established for the diagnosis of coronary artery disease (CAD) and risk-stratification in sinus rhythm (SR) patients.

Purpose

The aim of this study was to determine the impact of AF and coronary flow reserve (CFR) on revascularization in patients undergoing positron emission tomography (PET) MPI.

Methods

680 patients without a known history of CAD were included. 226 paroxysmal AF (PAF) and 114 long-standing persistent AF (LSPAF) patients were identified from a single-center prospective PET MPI registry and propensity matched in a 1:1 ratio to SR patients. The main indications for PET MPI were chest pain and dyspnea. Follow-up was obtained for downstream referral for invasive coronary angiography (CAG) and the occurrence of myocardial infarction (MI) or coronary revascularization.

Results

Compared with PAF, LSPAF patients were older (p=0.011) and more frequently male (p=0.031), with no significant differences in prior medical history and cardiac risk factors. The number of abnormal scans (infarction or ischemia) did not differ significantly between SR and AF, respectively 22.1% and 18.5% (p=0.253). The frequency of downstream CAG was comparable between the groups (p=0.298), with a significantly higher yield of obstructive CAD in the SR group as compared to PAF and LSPAF groups (63% vs 42% vs 36%, p=0.007). A low CFR (defined as CFR below the median of 2.4) in patients with SR showed significantly more revascularization compared with PAF and LSPAF (p&lt;0.001), although more patients with LSPAF and low CFR underwent CAG (p&lt;0.001). In patients with low CFR referred for CAG, the overall prevalence of obstructive coronary artery disease on CAG was 62%, with 30% for LSPAF, 52% for PAF and 78% for SR. There were no significant differences between SR, PAF and LSPAF in the occurrence of MI during a mean follow-up of 36 months (p=0.256).

Conclusion

A low CFR was only associated with a higher incidence of revascularization in patients with SR. Among patients with low CFR, LSPAF patients have the highest number of unnecessary CAGs as compared with SR and PAF.

Funding Acknowledgement

Type of funding sources: None.

Added value of coronary artery calcium score in the reporting of SPECT versus PET myocardial perfusion imaging

BACKGROUND

Knowledge of coronary artery calcium score (CACS) influences the interpretation of myocardial perfusion imaging (MPI) with SPECT; however, the impact on PET interpretation remains unclear. We compared the added value of CACS to reporting MPI using SPECT vs PET.

METHODS

We retrospectively included 412 patients. 206 patients who underwent Rb-82 PET were propensity-based matched to a cohort of 4018 patients who underwent cadmium-zinc-telluride SPECT MPI to obtain a comparable group of 206 SPECT patients. Next, we created four image sets: SPECT MPI-only, PET-only, SPECT + CACS, and PET + CACS. Two physicians interpreted the 824 images as normal, equivocal, or abnormal for ischemia or irreversible defects. Additionally, event rates were compared between PET and SPECT groups during 30-month follow-up.

RESULTS

PET yielded more scans interpreted as normal than SPECT (88% vs 80%, respectively, P = 0.015). Adding CACS to SPECT increased the percentage of normal scans to 86% (P = 0.014), whereas this effect was absent for PET (90%, P = 0.77). Annualized event rates for images interpreted as normal did not differ and varied between 0.7 and 2.0% (P > 0.084).

CONCLUSION

Adding CACS correctly increased the percentage of normal scans for SPECT MPI but not for PET, possibly limiting the effect of adding CACS to reporting PET.

Effect of temporal sampling protocols on myocardial blood flow measurements using Rubidium-82 PET

BACKGROUND

A variety of temporal sampling protocols is used worldwide to measure myocardial blood flow (MBF). Both the length and number of time frames in these protocols may alter MBF and myocardial flow reserve (MFR) measurements. We aimed to assess the effect of different clinically used temporal sampling protocols on MBF and MFR quantification in Rubidium-82 (Rb-82) PET imaging.

METHODS

We retrospectively included 20 patients referred for myocardial perfusion imaging using Rb-82 PET. A literature search was performed to identify appropriate sampling protocols. PET data were reconstructed using 14 selected temporal sampling protocols with time frames of 5-10 seconds in the first-pass phase and 30-120 seconds in the tissue phase. Rest and stress MBF and MFR were calculated for all protocols and compared to the reference protocol with 26 time frames.

RESULTS

MBF measurements differed (P ≤ 0.003) in six (43%) protocols in comparison to the reference protocol, with mean absolute relative differences up to 16% (range 5%-31%). Statistically significant differences were most frequently found for protocols with tissue phase time frames < 90 seconds. MFR did not differ (P ≥ 0.11) for any of the protocols.

CONCLUSIONS

Various temporal sampling protocols result in different MBF values using Rb-82 PET. MFR measurements were more robust to different temporal sampling protocols.

Low coronary flow reserve in patients with long-standing persistent atrial fibrillation is associated with worse clinical outcomes

Funding Acknowledgements

Type of funding sources: None.

Background / Introduction

Atrial fibrillation (AF) is associated with an increased risk of myocardial infarction, stroke and all-cause mortality. Myocardial perfusion imaging (MPI) is well-established for the diagnosis of coronary artery disease (CAD) and risk-stratification in sinus rhythm (SR) patients.

Purpose

The aim of this study was to determine the prognostic impact of AF and coronary flow reserve (CFR) in patients undergoing positron emission tomography (PET) MPI.

Methods

680 patients without a known history of CAD were included. 226 paroxysmal AF (PAF) and 114 long-standing persistent AF (LSPAF) patients were identified from a prospective PET MPI registry in the Isala Hospital and propensity matched in a 1:1 ratio to SR patients. The main indications for PET MPI were chest pain and dyspnea. Follow-up was obtained for the occurrence of major adverse cardiac and cerebrovascular events (MACCE, composite of myocardial infarction (MI), stroke/transient ischemic attack (TIA) or all-cause death).

Results

Compared with patients with PAF, patients with LSPAF were older (p=0.011) and more frequently male (p=0.031), with no significant differences in medical history. There were no significant differences between SR and AF in the occurrence of MACCE during a mean follow-up of 36 months. However, the incidence of downstream coronary angiography (p&lt;0.001) and MACCE (p=0.028) was higher in patients with LSPAF compared to those with PAF and SR. A low CFR (defined as CFR below the median of 2.4) in patients with LSPAF showed significantly more MACCE compared with SR and PAF (p&lt;0.001). Moreover, LSPAF was an independent predictor of MACCE (odds ratio 1.667, 95% confidence interval 1.028±2.705).

Conclusion

Low CFR in patients with LSPAF is associated with a higher incidence of MI, stroke/TIA and death compared with low and normal coronary flow parameters in patients with SR and PAF.

Value of SiPM PET in myocardial perfusion imaging using Rubidium-82

BACKGROUND

PET scanners using silicon photomultipliers with digital readout (SiPM PET) have an improved temporal and spatial resolution compared to PET scanners using conventional photomultiplier tubes (PMT PET). However, the effect on image quality and visibility of perfusion defects in myocardial perfusion imaging (MPI) is unknown. Our aim was to determine the value of a SiPM PET scanner in MPI.

METHODS

We prospectively included 30 patients who underwent rest and regadenoson-induced stress Rubidium-82 (Rb-82) MPI on the D690 PMT PET (GE Healthcare) and within three weeks on the Vereos SiPM PET (Philips Healthcare). Two expert readers scored the image quality and assessed the existence of possible defects. In addition, interpreter's confidence, myocardial blood flow (MBF), and myocardial flow reserve (MFR) values were compared.

RESULTS

Image quality improved (P = 0.03) using the Vereos as compared to the D690. Image quality of the Vereos and the D690 was graded fair in 20% and 10%, good in 60% and 50%, and excellent in 20% and 40%, respectively. Defect interpretation and interpreter's confidence did not differ between the D690 and the Vereos (P > 0.50). There were no significant differences in rest MBF (P ≥ 0.29), stress MBF (P ≥ 0.11), and MFR (P ≥ 0.51).

CONCLUSION

SiPM PET provides an improved image quality in comparison with PMT PET. Defect interpretation, interpreter's confidence, and absolute blood flow measurements were comparable between both systems. SiPM PET is therefore a reliable technique for MPI using Rb-82.

TRIAL REGISTRATION

ToetsingOnline NL63853.075.17. Registered 13 November, 2017.

Body weight-dependent Rubidium-82 activity results in constant image quality in myocardial perfusion imaging with PET

BACKGROUND

Clinical practice shows degrading image quality in heavier patients who undergo myocardial perfusion imaging (MPI) with Rubidium-82 (Rb-82) PET when using a fixed tracer activity. Our aim was to derive and validate a patient-specific activity protocol resulting in a constant image quality in PET MPI.

METHODS

We included 251 patients who underwent rest MPI with Rb-82 PET (Discovery 670, GE Healthcare). 132 patients were included retrospectively and were scanned using a fixed activity of 740 MBq. The total number of measured prompts was normalized to activity and correlated to body weight, mass per body length and body mass index to find the best predicting parameter. Next, a patient-specific activity was derived and subsequently validated in 119 additional patients. Image quality was scored by three experts on a four-point scale.

RESULTS

Both image quality and prompts decreased in heavier patients when using a fixed activity (p < .005). Body weight was used to derive a new activity formula: Activity = 8.3 MBq/kg. When applying this formula, both measured prompts and scored image quality became independent of body weight (p > .60).

CONCLUSION

Administrating a Rb-82 activity that linearly depends on body weight resulted in a constant image quality across all patients and is recommended.

Value of regional myocardial flow measurements using Rubidium-82 PET

Funding Acknowledgements

Type of funding sources: None.

Introduction

The combination of myocardial blood flow (MBF) measurements using Rubidium-82 (Rb-82) PET and visual assessment of the PET images is increasingly used due to its high diagnostic and prognostic value. Typically, flow measurements are calculated and used for the myocardium as a whole (global). However, small regional flow deficits may go unnoticed when only looking at global flow values.

Purpose

To compare the diagnostic value of regional and global myocardial flow measurements using Rb-82 PET in the detection of obstructive CAD.

Methods

 We retrospectively included 1034 patients with no history of coronary artery disease (CAD) referred for rest and regadenoson-induced stress Rb-82 PET/CT. MBFs were calculated using Lortie’s one-tissue compartment model. Myocardial flow reserve (MFR) was calculated as the ratio of MBF during stress and rest. Regional flow was determined per vessel and per segment. Vessel MFR was defined as the lowest flow reserve of LAD, LCX and RCA territories and segmental MFR as the lowest flow reserve in all 17 segments. Follow-up data were obtained from medical records. Patients were classified to have obstructive CAD if follow-up included a positive invasive coronary angiography (ICA), percutaneous coronary intervention (PCI), coronary artery bypass grafting (CABG) or all cause death. Receiver-operating characteristic (ROC) analyses were constructed to compare the diagnostic value of global and regional flow values.

Results

Follow-up was obtained in all 1034 patients and the median follow-up time was 2.1 years. Myocardial flow reserve values were significantly lower (p &lt; 0.001) in the 128 patients classified with obstructive CAD than in the 906 patients without obstructive CAD: global MFR  (median 1.9 [interquartile range 1.6-2.4] vs. 2.5 [2.1-2.9]); vessel MFR (1.6 [1.3-2.1]  vs. 2.3 [1.9-2.6]); Segmental MFR (1.3 [0.9-1.7] vs. 1.9 [1.6-2.2]). The area under the curve of vessel MFR (0.79 ± 0.02) and segmental MFR (0.81 ± 0.02) were similar but significantly (p &lt; 0.001) larger than the area of global MFR (0.75 ± 0.03), as shown in the Figure.

Conclusion

The diagnostic value improved with the use of regional MFR instead of global MFR measurements in the detection of obstructive CAD. Therefore, it seems that visual assessment of PET images can best be combined with regional flow measurements either on a per vessel or a per segment basis in Rubidium-82 PET myocardial perfusion imaging.

Long-term prognosis of zero coronary artery calcium score in symptomatic low to intermediate risk patients

Funding Acknowledgements

Type of funding sources: None.

Purpose/background

Absence of coronary artery calcium (CAC) has shown an excellent long-term prognosis with a low number of events in asymptomatic patients. However, long-term prognosis in stable symptomatic patients undergoing SPECT MPI with a zero CAC score remains unknown.

Methods

 We retrospectively analyzed 1600 low- to intermediate risk symptomatic patients referred for clinically indicated cardiac SPECT/CT imaging with a CAC score of zero. Long-term follow-up data were collected for the occurrence of all-cause mortality and major adverse cardiac events (MACE: any revascularization, non-fatal myocardial infarction or cardiac death).

Results

 The mean age was 54.7 ± 11 years and 71% were female. More than half of the patients (51%) had 2 or more traditional risk factors, mainly a positive family history (55%) and/or hypertension (49%).  Overall 12% had perfusion abnormalities, 98% of them were mild. During a mean follow-up of 8.6 ± 1.9 years MACE occurred in 42 patients (0.3% per year) and 85 patients died (0.6% per year). The predominant cause of death was cancer (40%). Cox proportional hazard model revealed that increasing age (HR: 1.05, 95% CI: 1.02-1.09) and current smoking status (HR: 3.58, 95% CI: 1.72-7.37) were independent predictors of MACE.  Pre-test probability (HR: 1.52, 95% CI: 0.82-2.82) and abnormal SPECT result (HR: 1.72, 95% CI: 0.88-3.37) were not associated with an increased risk of MACE.

Conclusion

Overall, stable symptomatic patients with a low-to intermediate risk and a CAC score of 0 have a) low likelihood of abnormal SPECT, and  b) excellent long-term prognosis of 0.3%/year irrespective of baseline pre-test probability and SPECT abnormalities. These findings support notion of CAC as gatekeeper for appropriate patient selection to avoid un-necessary downstream testing.

Value of coronary artery calcium score in reporting SPECT versus PET myocardial perfusion imaging

Funding Acknowledgements

Type of funding sources: None.

Background

Although it is well known that coronary artery calcium score (CACS) adds value to reporting myocardial perfusion imaging (MPI) SPECT, its added value to reporting PET MPI is not clear.

Purpose

Hence, our aim was determine the value of adding CACS in the assessment of PET MPI and SPECT MPI and compare the value between both modalities in a low-risk population.

Methods

We retrospectively included 412 patients, half of them underwent SPECT with CACS and half underwent Rubidium-82 PET with CACS. We created comparable groups using propensity matching, where the PET group was 1:1 matched to a comparable SPECT group, obtained from a large cohort of 4018. Next, we created two types of image sets for the 412 included patients: MPI-only and MPI + CACS. Two experienced physicians interpreted the 824 images as normal, equivocal or abnormal for  ischemia or irreversible defects and were blinded for the used modality. In addition, annualized event rates, defined as the occurrence of all-cause death, non-fatal myocardial infarction or revascularization therapy (PCI or CABG), were compared between the PET and SPECT groups using a follow-up period of 30 months.

Results

The percentage of scans interpreted as normal was 8% higher with PET-only than with SPECT-only (89 vs 80%, respectively, p = 0.014). Adding CACS to SPECT increased the percentage of scans interpreted as normal from 80% to 86% (p = 0.014), whereas this effect was absent for PET (p = 0.77). Adding CACS reduced the frequency of equivocal scans from 12% and 6% to 0% for both SPECT and PET, respectively. Furthermore, adding CACS resulted in 5% more abnormal interpreted scans for both PET (4.9 to 10%, p = 0.003) and SPECT (8.7 to 14%, p = 0.04). The annualized event rate was 2.7% for the SPECT and 3.5% for the PET group (p = 0.58). The annualized event rates for images interpreted as normal were comparable between all four types of image sets and varied between 0.7-2.0% (p &gt; 0.084). The annualized event rate for equivocal and abnormal scans was higher for PET-only (23%) compared to SPECT-only (4.8%, p &lt; 0.001). Moreover, the event rate for equivocal and abnormal SPECT + CACS  (8.6%) was also higher than for SPECT-only (4.8%, p = 0.04), whereas this difference was absent for PET (p = 0.07).

Conclusion

Adding CACS increases the percentage of scans interpreted as normal for SPECT MPI while the event rate remained unchanged. Adding CACS to PET did not influence the percentage of scans interpreted as normal, limiting the effect of adding CACS to PET in a low-risk population.

Prediction of obstructive coronary artery disease after Rb-82 PET myocardial perfusion imaging and coronary artery calcium scoring using machine learning

Funding Acknowledgements

Type of funding sources: None.

Background

Accurate risk stratification in patients with suspected stable coronary artery disease (CAD) is essential for choosing an appropriate treatment strategy but remains challenging in clinical practice.

Purpose

Our aim was to develop and validate a risk model to predict the presence of obstructive CAD after Rubidium-82 PET and a coronary artery calcium score (CACS) scan using a machine learning (ML) algorithm.

Methods

We retrospectively included 1007 patients without prior cardiovascular history and  a low-intermediate pre-test likelihood, referred for rest and regadenoson-induced stress Rubidium-82 PET combined with a CACS scan. Multiple features were included in the ML model; PET derived features such as summed difference score and flow values, CACS, cardiovascular risk factors (cigarette smoking, hypertension, hypercholesterolemia, diabetes, positive family history of CAD), medication; age; gender; body mass index; creatinine serum values; and visual PET interpretation. An XGBoost ML algorithm was developed using a subset of 805 patients to predict obstructive CAD by using 5-fold cross validation in combination with a grid search. Obstructive CAD during follow-up was defined as a significant stenosis during invasive coronary angiography, a percutaneous coronary intervention or a coronary artery bypass graft procedure. The ML algorithm was validated with unseen data of the remaining 202 patients.

Results

Application of the XGBoost algorithm resulted in an area under the curve (AUC) of 0.93 using the training data (n = 805) and an AUC of 0.89 using the unseen data (n = 202) in predicting obstructive CAD. The strongest predictors were the CAC-scores and quantitative PET derived features. The classical risk factors and medication hardly provided an added value in the prediction of obstructive CAD.

Conclusion

The developed ML algorithm is able to provide individualized risk stratification by predicting the probability of obstructive CAD.  Although validation with a larger dataset could result in a more well defined performance range, this model already shows potential to be implemented in the diagnostic workflow.

Predictors of severe stenosis at invasive coronary angiography in patients with normal myocardial perfusion imaging

Purpose

Normal myocardial perfusion imaging (MPI) is associated with excellent prognosis. However, in patients with persisting symptoms, it may be difficult to determine the patients in whom invasive angiography is justified to rule out false negative MPI. We evaluated predictors for severe stenosis at invasive angiography in patients with persisting symptoms after normal MPI.

Methods

229 consecutive patients with normal MPI, without previous bypass surgery, underwent invasive angiography within 6 months. Older age was defined as >65 years. Multivariable analyses were performed to adjust for differences in baseline variables.

Results

Mean age was 62 ± 11 years, 48% were women. Severe stenosis was observed in 34%, and of these patients 60% had single-vessel disease (not left main coronary artery disease). After adjusting for several variables, including diabetes, smoking status, hypertension and hypercholesterolaemia, predictors of severe stenosis were male gender, odds ratio (OR) 2.7 (95% confidence interval (CI) 1.5–4.9), older age, OR 1.9 (95% CI 1.02–3.54) previous PCI, OR 2.0 (95% CI 1.0–4.3) and typical angina, OR 2.5 (95% CI 1.4–4.6).

Conclusions

Increasing age, male gender, previous PCI and typical symptoms are predictors of severe stenosis at invasive coronary angiography in patients with normal MPI. The majority of these patients have single-vessel disease.

Effect of a patient-specific minimum activity in stress myocardial perfusion imaging using CZT-SPECT: Prognostic value, radiation dose, and scan outcome

BACKGROUND

SPECT Myocardial perfusion imaging (MPI) is associated with a relatively high radiation burden and decreasing image quality in heavy patients. Patient-specific low-activity protocols (PLAPs) are suggested but follow-up data is lacking. Our aim was to compare the use of a standard fixed-activity protocol (FAP) with a PLAP in cadmium zinc telluride (CZT)-SPECT MPI.

METHODS

We retrospectively included 1255 consecutive patients who underwent CZT-SPECT stress-optional rest MPI. 668 Patients were scanned using FAP (370 MBq) and 587 patients using PLAP (2.25 MBq·kg-1). Percentage of scans interpreted as normal, radiation dose, and 1-year follow-up including hard event rates (all-cause death or non-fatal myocardial infarction) were collected and compared.

RESULTS

The percentage of scans interpreted as normal was 67% in FAP and 70% in PLAP groups (P = .29). The annualized hard event rates in these patients were 1.0% in the FAP and 0.9% in the PLAP group (P = .86). However, the mean radiation dose decreased by 23% for stress-only and by 15% to 2.6 mSv for stress-optional rest MPI after introduction of the PLAP (p<0.001).

CONCLUSIONS

Introduction of a patient-specific low-activity protocol does not affect the percentage of scans interpreted as normal or prognosis but significantly lowers the radiation dose for CZT-SPECT MPI.

Value of attenuation correction in stress-only myocardial perfusion imaging using CZT-SPECT

BACKGROUND

Attenuation correction (AC) improves the diagnostic outcome of stress-only myocardial perfusion imaging (MPI) using conventional SPECT. Our aim was to determine the value of AC using a cadmium zinc telluride-based (CZT)-SPECT camera.

METHODS AND RESULTS

We retrospectively included 107 consecutive patients who underwent stress-optional rest MPI CZT-SPECT/CT. Next, we created three types of images for each patient; (1) only displaying reconstructed data without the CT-based AC (NC), (2) only displaying AC, and (3) with both NC and AC (NC + AC). Next, two experienced physicians visually interpreted these 321 randomized images as normal, equivocal, or abnormal. Image outcome was compared with all hard events over a mean follow-up time of 47.7 ± 9.8 months. The percentage of images interpreted as normal increased from 45% using the NC images to 72% using AC and to 67% using NC + AC images (P < .001). Hard event hazard ratios for images interpreted as normal were not different between using NC and AC (1.01, P = .99), or NC and NC + AC images (0.97, P = .97).

CONCLUSIONS

AC lowers the need for additional rest imaging in stress-first MPI using CZT-SPECT, while long-term patient outcome remained identical. Use of AC reduces the need for additional rest imaging, decreasing the mean effective dose by up to 1.2 mSv.

Visual estimation of coronary calcium on computed tomography for attenuation correction

BACKGROUND

The coronary calcium score (CCS) provides independent diagnostic and prognostic information on top of myocardial perfusion imaging (MPI) in patients suspected for coronary artery disease, but requires an additional computed tomography (CT) scan.

OBJECTIVE

We investigated the accuracy and inter-reader reproducibility of visual estimation of the CCS on the CT used for attenuation correction.

METHODS

250 patients undergoing single photon emission computed tomography MPI and Agatston CCS were included. The CCS was also visually estimated on the CT for attenuation correction by two separate readers blinded to the Agatston CCS, and was categorized into a six-point scale (0, 1-10, 11-100, 101-400, 401-1000 and > 1000).

RESULTS

The median Agatston CCS was 82 [25th-75th percentile: 0-562], with a range from 0 to 7287. Of the visually estimated CCS, 60% (reader 1) and 65% (reader 2) were classified correctly into the 6 categories. 93% (reader 1) and 88% (reader 2) of the visually estimated CCS did not vary by more than one category from the Agatston CCS. The intraclass correlation coefficient for agreement between the Agatston CCS and the visually estimated CCS was 0.95 for reader 1 and 0.94 for reader 2. The intraclass correlation coefficient for inter-reader reproducibility of the visually estimated CCS was 0.96.

CONCLUSION

The CCS can be accurately estimated on the CT for attenuation correction, as high agreement is demonstrated with the Agatston CCS and inter-reader reproducibility is excellent. If no traditional Agatston CCS is performed, the degree of atherosclerosis should be assessed by means of estimating CCS on the CT for attenuation correction.

Development and validation of a patient-tailored dose regime in myocardial perfusion imaging using CZT-SPECT

BACKGROUND

Guidelines for SPECT myocardial perfusion imaging (MPI) traditionally recommend a fixed tracer dose. Yet, clinical practice shows degraded image quality in heavier patients. The aim was to optimize and validate the tracer dose and scan time to obtain a constant image quality less dependent on patients' physical characteristics.

METHODS

125 patients underwent Cadmium Zinc Telluride (CZT)-SPECT stress MPI using a fixed Tc-99m-tetrofosmin tracer dose. Image quality was scored by three physicians on a 4-point grading scale and related to the number of photon counts normalized to tracer dose and scan time. Counts were correlated with various patient-specific parameters dealing with patient size and weight to find the best predicting parameter. From these data, a formula to provide constant image quality was derived, and subsequently tested in 92 new patients.

RESULTS

Degradation in image quality and photon counts was observed for heavier patients for all patients' specific parameters (P < .01). We found body weight to be the best-predicting parameter for image quality and derived a new dose formula. After applying this new body weight-depended tracer dose and scan time in a new group, image quality was found to be constant (P > .19) in all patients.

CONCLUSIONS

Also in CZT SPECT image quality decreases with weight. The use of a tracer dose and scan time that depends linearly on patient's body weight corrected for the varying image quality in CZT-SPECT MPI. This leads to better radiation exposure justification.

[Regadenoson as a new stress agent in myocardial perfusion imaging. Initial experience in The Netherlands]

OBJECTIVE

Regadenoson is a recently approved selective adenosine-2A receptor agonist to induce pharmacological stress in myocardial perfusion imaging (MPI) procedures using a single bolus injection.

MATERIAL AND METHODS

We included 123 patients referred for MPI because of suspected coronary arterial disease (CAD). Of these, 66 patients underwent a regadenoson stress test and 57 patients underwent an adenosine stress test preceding standard myocardial SPECT imaging. Technicians, physicians and patients were asked to report their experience using questionnaires.

RESULTS

As compared to adenosine, regadenoson did not produce any atrio-ventricular block (0 vs. 10% with adenosine), but did produce minor tachycardia and minimal blood pressure changes while all other side effects were milder and shorter. There were fewer patients with severe complaints after taking regadenoson than adenosine (17% vs. 32%, respectively, p<0.01). The most frequent complaint reported was dyspnea, followed by flushing and chest pain. However, when they did occur, they usually disappeared rapidly. The overall symptom score, including severity and duration of side effects, was significantly lower after regadenoson than after adenosine (6.7±6.3 vs. 10.0±7.9, respectively; p<0.01.) SPECT imaging results were similar. The regadenoson procedure was faster and more practical.

CONCLUSION

Regadenoson, the new selective adenosine-2A receptor agonist, is a stress agent for MPI with a patient- and department friendly profile.

[Striatopallidodentate calcinosis, hypoparathyroidism and neurological features: a case series study]

INTRODUCTION

The respective roles of hypocalcemia and intracerebral calcifications in the occurrence of various neurological manifestations in hypoparathyroidism is not entirely clear. Nevertheless, therapeutic and prognostic implications are important.

OBJECTIVES

We analyze the neurological clinical aspects observed in hypoparathyroidism and correlate them to the biological calcium abnormality and radiological CT scan findings. We also compare these results with data reported in the idiopathic form of striatopallidodentate calcinosis.

PATIENTS

The neurological clinical, CT scan findings and outcome have been retrospectively studied in patients recruited during 13 years (2000-2012) for neurological features associated with hypoparathyroidism or pseudohypoparathyroidism.

RESULTS

Twelve patients with primary hypoparathyroidism (n=5), secondary to thyroidectomy (n=4) and pseudohypoparathyroidism (n=3) were studied. The sex-ratio was 1 and mean age was 39 years. All patients had a tetany, 60% had epilepsy, associated in one patient with "benign" intracranial hypertension; 50% had behavioral changes. Response to calcium therapy was excellent for all these events. Moderate cognitive deficit was noted in three patients (25%), parkinsonism in two patients and hyperkinetic movement disorders in one other. These events were not responsive to calcium therapy and were more common in cases of extensive brain calcifications and in patients who had pseudohypoparathroidism.

COMMENTS

This study suggests that, in patients with hypoparathyroidism, epilepsy and psychiatric disorders are induced by hypocalcemia and reversible after its correction. Cognitive and extrapyramidal impairment seem to be related to the progressive extension of intracerebral calcification, particularly in patients with a late diagnosis. In patients with pseudohypoparathyroidism, this finding is different because of the contribution of other factors, specific to this disease.

Prevalence and predictors of bridging of coronary arteries in a large Indonesian population, as detected by 64-slice computed tomography scan

BACKGROUND

Multislice computed tomography (MSCT) can be used to detect myocardial bridging (MB) of coronary arteries. However, most published studies included small cohorts and did not collect data about predictors. We investigated prevalence and predictors of MB in an Indonesian population.

METHODS

All patients who had MSCT at Cinere Hospital, Jakarta, Indonesia between 2006 and 2009 were included in a prospective registry. MB was defined when at least half of the coronary artery was imbedded within the myocardium with a normal epicardial course of the proximal and distal portion.

RESULTS

Of the 934 patients (mean age 53 years, 37.8 % female), MB could be observed in 152 patients (16.3 %). Patients with MB were younger compared with those without MB. Coronary risk factors were not different between the two groups. Coronary calcifications and moderate to severe coronary stenoses were less prevalent in patients with MB, also after adjusting for differences in age. At the time of diagnosis, only a few patients with MB were treated with beta-blockers (35 %) or calcium channel blockers (13 %).

CONCLUSIONS

Prevalence of myocardial bridging as detected by MSCT is relatively high. Patients with MB were younger and had a lower prevalence of coronary sclerosis. MB could be the cause of their unexplained symptoms. Follow-up studies are necessary to assess the symptoms of these patients, their response to treatment and the incidence of (coronary) events. MSCT can be used to identify patients for potential new treatment strategies.

[Severe neonatal myasthenia with arthrogryposis]

Maternal myasthenia gravis has been associated with the presence of neonatal myasthania and sometimes fetal congenital anomalies. The purpose of this paper is to present an infant with multiple deformations born to a mother with myasthenia gravis. The infant presented with arthrogryposis multiplex and pulmonary hypoplasia. The new born died within the first day of life. Twenty-seven other cases of neonatal myasthenia with arthrogryposis have been reported. Twenty-two of them were stillborn or died. The surviving children needed ventilatory assistance for a long period.