Protocol for measuring myocardial blood flow by PET/CT in cats

Purpose: The aim of this study was to establish a protocol for measuring myocardial blood flow (MBF) by PET/CT in healthy cats. The rationale was its future use in Maine Coon cats with hypertrophic cardiomyopathy (HCM) as a model for human HCM. Methods: MBF was measured in nine anaesthetized healthy cats using a PET/CT scanner and 13NH3 at rest and during adenosine infusion. Each cat was randomly assigned to receive vasodilator stress with two or three adenosine infusions at the following rates (μg/kg per minute): 140 (Ado1, standard rate for humans), 280 (Ado2, twice the human standard rate), 560 (Ado4), 840 (Ado6) and 1,120 (Ado8). Results: The median MBF at rest was 1.26ml/min per g (n = 9; range 0.88-1.72ml/min per g). There was no significant difference at Ado1 (n = 3; median 1.35, range 0.93-1.55ml/min per g; ns) but MBF was significantly greater at Ado2 (n = 6; 2.16, range 1.35-2.68ml/min per g; p < 0.05) and Ado4 (n = 6; 2.11, 1.92-2.45ml/min per g; p < 0.05). Large ranges of MBF values at Ado6 (n = 4; 2.53, 2.32-5.63ml/min per g; ns) and Ado8 (n = 3; 2.21, 1.92-5.70ml/min per g; ns) were noted. Observed adverse effects, including hypotension, AV-block and ventricular premature contractions, were all mild, of short duration and immediately reversed after cessation of the adenosine infusion. Conclusion: MBF can be safely measured in cats using PET. An intravenous adenosine infusion at a rate of 280μg/kg per minute seems most appropriate to induce maximal hyperaemic MBF response in healthy cats. Higher adenosine rates appear less suitable as they are associated with a large heterogeneity in flow increase and rate pressure product, most probably due to the large variability in haemodynamic and heart rate respons

Coronary 64-slice CT angiography predicts outcome in patients with known or suspected coronary artery disease

The aim of this study was to assess the prognostic value of 64-slice CT angiography (CTA) in patients with known or suspected coronary artery disease (CAD). Sixty-four-slice coronary CTA was performed in 220 patients [mean age 63 ± 11years, 77 (35%) female] with known or suspected CAD. CTA images were analyzed with regard to the presence and number of coronary lesions. Patients were followed-up for the occurrence of the following clinical endpoints: death, nonfatal myocardial infarction, unstable angina, and coronary revascularization. During a mean follow-up of 14 ± 4months, 59 patients (27%) reached at least one of the predefined clinical endpoints. Patients with abnormal coronary arteries on CTA (i.e., presence of coronary plaques) had a 1st-year event rate of 34%, whereas in patients with normal coronary arteries no events occurred (event rate, 0%, p < 0.001). Similarly, obstructive lesions (≥50% luminal narrowing) on CTA were associated with a high first-year event rate (59%) compared to patients without stenoses (3%, p < 0.001). The presence of obstructive lesions was a significant independent predictor of an adverse cardiac outcome. Sixty-four-slice CTA predicts cardiac events in patients with known or suspected CAD. Conversely, patients with normal coronary arteries on CTA have an excellent mid-term prognosi

Assessment of myocardial perfusion by dynamic O-15-labeled water PET imaging: Validation of a new fast factor analysis

Background: Factor analysis (FA) is an established method for separating myocardium from blood pool by use of oxygen 15-labeled water and positron emission tomography for analyzing myocardial blood flow (MBF). Conventional FA methods generating images from sinograms (sinoFA) are time-consuming, whereas FA can be performed on the reconstructed images (reconFA) in a fraction of time. We validated the MBF values obtained by reconFA versus sinoFA. Methods and Results: In 23 volunteers (mean age, 26.6±3.4 years) MBF was calculated from sinoFA and reconFA and blindly reanalyzed 1 month later by the same observer. Intraobserver agreement and reconFA-versus-sinoFA agreement were assessed according to Bland and Altman (BA). Reproducibility proved excellent for global sinoFA (r=0.968; P<.001; BA limits, −0.617 to 0.676 mL·min−1·g−1) and slightly superior for reconFA (r=0.979; P<.001; BA limits, −0.538 to 0.558 mL·min−1·g−1), with wider limits of agreement for segmental MBF from sinoFA (r=0.777; P<.001; BA limits, −1.676 to 1.656 mL·min−1·g−1) and reconFA (r=0.844; P<.001; BA limits, −1.999 to 1.992 mL·min−1·g−1). In addition, sinoFA and reconFA showed excellent correlation (r=0.975, P<.001) and agreement (BA limits, −0.528 to 0.648 mL·min−1·g−1) for global and segmental values (r=0.955; P<.001; BA limits, −1.371 to 1.491 mL·min−1·g−1). Conclusions: Use of reconFA allows rapid and reliable quantitative MBF assessment with O-15-labeled wate

Accuracy of 64-slice CT angiography for the detection of functionally relevant coronary stenoses as assessed with myocardial perfusion SPECT

Purpose: CT angiography (CTA) offers a valuable alternative for the diagnosis of CAD but its value in the detection of functionally relevant coronary stenoses remains uncertain. We prospectively compared the accuracy of 64-slice CTA with that of myocardial perfusion imaging (MPI) using 99mTc-tetrofosmin-SPECT as the gold standard for the detection of functionally relevant coronary artery disease (CAD). Methods: MPI and 64-slice CT were performed in 100 consecutive patients. CTA lesions were analysed quantitatively and area stenoses ≥50% and ≥75% were compared with the MPI findings. Results: In 23 patients, MPI perfusion defects were found (12 reversible, 13 fixed). A total of 399 coronary arteries and 1,386 segments was analysed. Eighty-four segments (6.1%) in 23 coronary arteries (5.8%) of nine patients (9.0%) were excluded owing to insufficient image quality. In the remaining 1,302 segments, quantitative CTA revealed stenoses ≥50% in 57 of 376 coronary arteries (15.2%) and stenoses ≥75% in 32 (8.5%) coronary arteries. Using a cut-off at ≥75% area stenosis, CTA yielded the following sensitivity, specificity, negative (NPV) and positive predictive value (PPV), and accuracy for the detection of any (fixed and reversible) MPI defect: by patient, 75%, 90%, 93%, 68% and 87%, respectively; by artery, 76%, 95%, 99%, 50% and 94%, respectively. Conclusion: Sixty-four-slice CTA is a reliable tool to rule out functionally relevant CAD in a non-selected population with an intermediate pretest likelihood of disease. However, an abnormal CTA is a poor predictor of ischaemi

Optimal image reconstruction intervals for non-invasive coronary angiography with 64-slice CT

The reconstruction intervals providing best image quality for non-invasive coronary angiography with 64-slice computed tomography (CT) were evaluated. Contrast-enhanced, retrospectively electrocardiography (ECG)-gated 64-slice CT coronary angiography was performed in 80 patients (47 male, 33 female; mean age 62.1±10.6years). Thirteen data sets were reconstructed in 5% increments from 20 to 80% of the R-R interval. Depending on the average heart rate during scanning, patients were grouped as <65bpm (n=49) and ≥65bpm (n=31). Two blinded and independent readers assessed the image quality of each coronary segment with a diameter ≥1.5mm using the following scores: 1, no motion artifacts; 2, minor artifacts; 3, moderate artifacts; 4, severe artifacts; and 5, not evaluative. The average heart rate was 63.3±13.1bpm (range 38-102). Acceptable image quality (scores 1-3) was achieved in 99.1% of all coronary segments (1,162/1,172; mean image quality score 1.55±0.77) in the best reconstruction interval. Best image quality was found at 60% and 65% of the R-R interval for all patients and for each heart rate subgroup, whereas motion artifacts occurred significantly more often (P<0.01) at other reconstruction intervals. At heart rates <65bpm, acceptable image quality was found in all coronary segments at 60%. At heart rates ≥65bpm, the whole coronary artery tree could be visualized with acceptable image quality in 87% (27/31) of the patients at 60%, while ten segments in four patients were rated as non-diagnostic (scores 4-5) at any reconstruction interval. In conclusion, 64-slice CT coronary angiography provides best overall image quality in mid-diastole. At heart rates <65bpm, diagnostic image quality of all coronary segments can be obtained at a single reconstruction interval of 60

Diagnostic accuracy of myocardial perfusion imaging with single photon emission computed tomography and positron emission tomography: a comparison with coronary angiography

Objective The aim of this study was to compare the diagnostic accuracy of myocardial perfusion imaging (MPI) by positron emission tomography (PET) with the diagnostic accuracy of MPI by single photon emission computed tomography (SPECT) in two comparable patient cohorts, using coronary angiography (CA) as the standard of reference. Methods A "SPECT-group” of 80 patients (15 female, 65 male; mean age 60±9years) and a "PET-group” of 70 patients (14 female, 56 male; mean age 57±10years) underwent a one day stress/rest examination either with attenuation-corrected 13N-ammonia PET or attenuation-corrected 201TlCl SPECT or 99mTc-hexakis-methoxy-isobutyl-isonitril (MIBI) SPECT. PET and SPECT results were semiquantitatively graded using a 6-segment heart model. All patients underwent CA, and stenoses were graded as a diameter reduction ≥50%. Results Coronary findings between both groups did not significantly differ at CA. For the SPECT-group overall sensitivity and specificity for localisation of stenoses was 77% and 84%. Respective values for the PET-group were 97% and 84%. The specificity of MPI by SPECT in the detection of ischemia was 74% and 91% for MPI by PET. The diagnostic accuracy of MPI improves when the individual coronary dominance and previous coronary revascularisations are taken into account. Conclusion MPI by 13N-ammonia PET is more sensitive in the detection and localisation of coronary stenoses, and more specific in the detection of ischemia than MPI by 201TlCl/99mMIBI SPEC

Coronary CT angiography and myocardial perfusion imaging to detect flow-limiting stenoses: a potential gatekeeper for coronary revascularization?

Aims To evaluate the diagnostic accuracy of a combined non-invasive assessment of coronary artery disease with coronary CT angiography (CTA) and myocardial perfusion imaging (MPI) for the detection of flow-limiting coronary stenoses and its potential as a gatekeeper for invasive examination and treatment. Methods and results In 78 patients (mean age 65 ± 9 years) referred for coronary angiography (CA), additional CTA and MPI (using single-photon emission-computed tomography) were performed and the findings not communicated. Detection of flow-limiting stenoses (justifying revascularization) by the combination of CTA and MPI (CTA/MPI) was compared with the combination of quantitative coronary angiography (QCA) plus MPI (QCA/MPI), which served as standard of reference. The findings of both combinations were related to the treatment strategy (revascularization vs. medical treatment) chosen in the catheterization laboratory based on the CA findings. Sensitivity, specificity, positive and negative predictive value, and accuracy of CTA/MPI for the detection of flow-limiting coronary stenoses were 100% each. More than half of revascularization procedures (21/40, 53%) was performed in patients without flow-limiting stenoses and 76% (47/62) of revascularized vessels were not associated with ischaemia on MPI. Conclusion The combined non-invasive approach CTA/MPI has an excellent accuracy to detect flow-limiting coronary stenoses compared with QCA/MPI and its use as a gatekeeper appears to make a substantial part of revascularization procedures redundan

Influence of cardiac hemodynamic parameters on coronary artery opacification with 64-slice computed tomography

The purpose of this study was to evaluate the influence of ejection fraction (EF), stroke volume (SV), heart rate, and cardiac output (CO) on coronary artery opacification with 64-slice computed tomography (CT). Sixty patients underwent, retrospectively, electrocardiography-gated 64-slice CT coronary angiography. Left ventricular EF, SV, and CO were calculated with semi-automated software. Attenuation values were measured and contrast-to-noise ratios (CNRs) were calculated in the proximal right coronary artery (RCA) and left main artery (LMA). Mean EF during scanning was 61.5±12.4%, SV was 63.2±15.6ml, heart rate was 62.5±11.8beats per minute (bpm), and CO was 3.88±1.06l/min. There was no significant correlation between the EF and heart rate and the attenuation and CNR in either coronary artery. A significant negative correlation was found in both arteries between SV and attenuation (RCA r=−0.26, P<0.05; LMA r=−0.34, P<0.01) and between SV and CNR (RCA r=−0.26, P<0.05; LMA r=−0.26, P<0.05). Similarly, a significant negative correlation was found between the CO and attenuation (RCA r=−0.42, P<0.05; LMA r=−0.56, P<0.001) and between the CO and CNR (RCA r=−0.39, P<0.05; LMA r=−0.44, P<0.001). The actual hemodynamic status of the patient influences the coronary artery opacification with 64-slice CT, in that vessel opacification decreases as SV and CO increas

Use of coronary calcium score scans from stand-alone multislice computed tomography for attenuation correction of myocardial perfusion SPECT

Purpose: To evaluate the use of CT attenuation maps, generated from coronary calcium scoring (CCS) scans at in- and expiration with a 64-slice CT scanner, for attenuation correction (AC) of myocardial perfusion SPECT images. Methods: Thirty-two consecutive patients underwent 99mTc-tetrofosmin gated adenosine stress/rest SPECT scan on an Infinia Hawkeye SPECT-CT device (GE Medical Systems) followed by CCS and CT angiography on a 64-slice CT. AC of the iteratively reconstructed images was performed with AC maps obtained: (a) from the "Hawkeye” low-resolution X-ray CT facility attached to the Infinia camera (IRAC); (b) from the CCS scan acquired on a 64-slice CT scanner during maximal inspiration (ACINSP) and (c) during normal expiration (ACEXP). Automatically determined uptake values of stress scans (QPS, Cedars Medical Sinai) from ACINSP and ACEXP were compared with IRAC. Agatston score (AS) values using ACINSPversus ACEXP were also compared. Results: ACINSP and ACEXP resulted in identical findings versus IRAC by visual analysis. A good correlation for uptake values between IRAC and ACINSP was found (apex, r=0.92; anterior, r=0.85; septal, r=0.91; lateral, r=0.86; inferior, r=0.90; all p<0.0001). The correlation was even closer between IRAC and ACEXP (apex, r=0.97; anterior, r=0.91; septal, r=0.94; lateral, r=0.92; inferior, r=0.97; all p<0.0001). The mean AS during inspiration (319±737) and expiration(317±778) was comparable (p=NS). Conclusion: Attenuation maps from CCS allow accurate AC of SPECT MPI images. ACEXP proved superior to ACINSP, suggesting that in hybrid scans CCS may be performed during normal expiration to allow its additional use for AC of SPECT MP

Validation of a new cardiac image fusion software for three-dimensional integration of myocardial perfusion SPECT and stand-alone 64-slice CT angiography

Purpose: Combining the functional information of SPECT myocardial perfusion imaging (SPECT-MPI) and the morphological information of coronary CT angiography (CTA) may allow easier evaluation of the spatial relationship between coronary stenoses and perfusion defects. The aim of the present study was the validation of a novel software solution for three-dimensional (3D) image fusion of SPECT-MPI and CTA. Methods: SPECT-MPI with adenosine stress/rest 99mTc-tetrofosmin was fused with 64-slice CTA in 15 consecutive patients with a single perfusion defect and a single significant coronary artery stenosis (≥50% diameter stenosis). 3D fused SPECT/CT images were analysed by two independent observers with regard to superposition of the stenosed vessel onto the myocardial perfusion defect. Interobserver variability was assessed by recording the X, Y, Z coordinates for the origin of the stenosed coronary artery and the centre of the perfusion defect and measuring the distance between the two landmarks. Results: SPECT-MPI revealed a fixed defect in seven patients, a reversible defect in five patients and a mixed defect in three patients and CTA documented a significant stenosis in the respective subtending coronary artery. 3D fused SPECT/CT images showed a match of coronary lesion and perfusion defect in each patient and the fusion process took less than 15min. Interobserver variability was excellent for landmark detection (r = 1.00 and r = 0.99, p < 0.0001) and very good for the 3D distance between the two landmarks (r = 0.94, p < 0.001). Conclusion: 3D SPECT/CT image fusion is feasible, reproducible and allows correct superposition of SPECT segments onto cardiac CT anatom