PET/CT challenge for the non-invasive diagnosis of coronary artery disease

This review will focus on the clinical potential of PET/CT for the characterization of cardiovascular diseases. We describe the technical challenges of combining instrumentation with very different imaging performance and discuss the clinical applications in the field of cardiology.     

Cardiac PET/CT for the evaluation of known or suspected coronary artery disease

Positron emission tomography (PET) is increasingly being applied in the evaluation of myocardial perfusion. Cardiac PET can be performed with an increasing variety of cyclotron- and generator-produced radiotracers. Compared with single photon emission computed tomography, PET offers lower radiation exposure, fewer artifacts, improved spatial resolution, and, most important, improved diagnostic performance. With its capacity to quantify rest-peak stress left ventricular systolic function as well as coronary flow reserve, PET is superior to other methods for the detection of multivessel coronary artery disease and, potentially, for risk stratification. Coronary artery calcium scoring may be included for further risk stratification in patients with normal perfusion imaging findings. Furthermore, PET allows quantification of absolute myocardial perfusion, which also carries substantial prognostic value. Hybrid PET-computed tomography scanners allow functional evaluation of myocardial perfusion combined with anatomic characterization of the epicardial coronary arteries, thereby offering great potential for both diagnosis and management. Additional studies to further validate the prognostic value and cost effectiveness of PET are warranted.     

Hybrid CT angiography and quantitative 15O-water PET for assessment of coronary artery disease: comparison with quantitative coronary angiography

Purpose

CT angiography (CTA) can rule out significant stenoses with a very high reliability, whereas its ability to confirm significant stenoses is suboptimal. In contrast, measurements of myocardial blood flow (MBF) provide information on the haemodynamic consequences of stenoses. Therefore, a combination of the two might improve diagnostic accuracy. We conducted a head-to-head comparison of CTA, measurement of MBF by ¹⁵O-water PET, and hybrid PET/CTA for the detection of significant coronary artery stenoses.

Methods

The study group comprised 44 outpatients scheduled for invasive coronary angiography (ICA) with an intermediate pretest likelihood of coronary artery disease. The patients underwent 64-slice CTA and baseline and hyperaemic PET before ICA with quantitative coronary angiography analysis.

Results

On a per-patient basis, the negative predictive values (NPV; 95 % confidence intervals in parentheses) were 88 % (64 – 97 %) for CTA, 90 % (71 – 97%) for PET and 92 % (74 – 98%) for PET/CTA, and the positive predictive values (PPV) were 71 % (53 – 85%) for CTA, 87 % (68 – 95%) for PET and 100 % (84 – 100%) for PET/CTA. Similarly, on a per-vessel basis the NPVs (which were generally high) were 97 % (94 – 100%) for CTA, 95 % (90 – 99%) for PET and 97 % (95 – 100%) for PET/CTA, and the PPVs (which were lower, but higher with PET/CTA) were 53 % (39 – 66%) for CTA, 53 % (40 – 66%) for PET and 85 % (73 – 97%) for PET/CTA. In six patients, CTA analysis was hampered by the presence of severe calcifications. However, with the addition of the PET data, all six patients were correctly categorized.

Conclusion

Cardiac quantitative hybrid PET/CTA imaging has better diagnostic accuracy than CTA alone and PET alone. CTA has a suboptimal PPV, suggesting that hybrid PET/CTA imaging should be used to assess the significance of coronary stenoses diagnosed by CTA.     

Coronary artery calcium scoring vs. coronary CT angiography for the assessment of occupationally significant coronary artery disease

BackgroundExisting pathways for investigating coronary artery disease (CAD) in individuals undertaking high-hazard employment are currently guided by coronary artery calcium scoring (CACS) or coronary CT angiography (CTA). The optimal pathway has not been established.AimTo compare the diagnostic outcome and occupational recommendations from two differing investigative pathways for the investigation of CAD in a cohort of high-hazard employees.MethodsWe collected CACS and coronary CTA data from three clinics across two Hospitals on 200 consecutive individuals employed in high-hazard occupations to confirm/exclude occupationally significant CAD. High-hazard occupations were grouped into civil/military pilots and aircraft controllers (n ?= ?106); non-pilot aircrew (NPA) (n ?= ?26); and ground-based (military) personnel (GBP) (n ?= ?52). Demographics, referral indications and recommended occupational outcomes between pathways were compared between groups.ResultsThe CACS pathway led to more than double the number of individuals being returned to partial or full employment, compared with the coronary CTA pathway (OR 2.10, [95%CI 1.54–2.85], P ?< ?0.001). This effect was seen in all sub-groups.Of the 177 subjects that would have been returned to full employment using CACS, 21 (11.9%) would have been occupationally restricted on the basis of significant non-calcified plaque disease using coronary CTA (11.4% pilots/controllers; 19.2% non-pilot aircrew, and 7.7% ground-based personnel).ConclusionUsing CACS to determine the presence of occupational CAD risks returning individuals to roles with occupationally significant CAD that may lead to an unacceptably high likelihood of an incapacitating/distracting acute coronary event. Coronary CTA appears to be a more reliable, non-invasive imaging modality for confirming or excluding occupationally significant CAD in high-hazard employees.     

CT冠状动脉成像在冠心病诊断中的应用

目的:研究CT冠状动脉成像在冠心病早期诊断冠状动脉狭窄定性定量判读的作用。方法:对34例临床未发生急性冠脉综合征的冠心病患者,先后进行冠状动脉造影、128排双源CT冠状动脉成像。以冠状动脉造影为"金标准",计算CT冠状动脉成像敏感性、特异性、阳性预测值、阴性预测值。结果:①与冠状动脉造影相比,CT冠状动脉成像的敏感性为68%,特异性为97%,阳性预测值为89%,阴性预测值为90%。②CT冠状动脉成像有65个血管段图像质量差,约占12%,造成图像质量差的原因主要为钙化,心跳、呼吸伪影,少部分为管腔显示不良。结论:冠心病早期诊断中,CT冠状动脉成像可用作冠状动脉造影前筛选,CT冠状动脉成像阴性的患者不必行冠状动脉造影检查;CT冠状动脉成像阳性的患者,可行冠状动脉造影进一步确认病变。     

PET/CT colonography in patients with colorectal polyps: a feasibility study

PURPOSE: To examine: (1) the feasibility of PET/CT colonography (PET/CTc) in patients with colorectal polyps; (2) the impact of metabolic information on CTc interpretation and, conversely, the impact of morphological information on PET characterisation of focal colorectal uptake. METHODS: Ten patients with colorectal polyps underwent PET/CTc, followed within 3 h by therapeutic conventional colonoscopy (CC). A radiologist and a nuclear medicine physician analysed the PET/CTc images. The agreement of morphological and metabolic information in the colon and rectum was evaluated. The sensitivity and specificity of PET, CT and PET/CT were calculated for colorectal polyps. RESULTS: Seventeen polypoid lesions were identified at CC: six< or =5 mm, six between 6 and 9 mm, and five > or =10 mm (four hyperplastic polyps, 11 tubular adenomas, one adenocarcinoma and one submucosal lipoma). A total of 20 scans (supine and prone) were performed in the ten patients: the agreement of morphological and metabolic information was excellent in 17 scans, good in two and moderate in one. PET/CTc showed a sensitivity of 91% for lesions > or =6 mm and a specificity of 100%. The metabolic information did not disclose any further polyps missed on CTc. The morphological information permitted correct classification of all eight instances of focal radiotracer uptake. CONCLUSION: PET/CTc is a feasible study. Adding a colonographic protocol to PET/CT images seems to allow correct characterisation of all cases of colorectal focal radiotracer uptake. The metabolic information does not seem to increase the accuracy of CTc.     

Diagnosing coronary artery disease with hybrid PET/CT: It takes two to tango

The noninvasive diagnosis of coronary artery disease (CAD) is a challenging task. Although a large armamentarium of imaging modalities is available to evaluate the functional consequences of the extent and severity of CAD, cardiac perfusion positron emission tomography (PET) is considered the gold standard for this purpose. Alternatively, noninvasive anatomical imaging of coronary atherosclerosis with coronary computed tomography angiography (CCTA) has recently been successfully implemented in clinical practice. Although each of these diagnostic approaches has its own merits and caveats, functional and morphological imaging techniques provide fundamentally different insights into the disease process and should be considered to be complementary rather than overlapping. Hybrid imaging with PET/CT offers the possibility to evaluate both aspects nearly simultaneously, and studies have demonstrated that such a comprehensive assessment results in superior diagnostic accuracy, better prognostication, and helps in guiding clinical patient management. The aim of this review is to discuss the value of stand-alone CCTA and PET in CAD, and to summarize the available data on the surplus value of hybrid PET/CT including its strengths and limitations.     

Integrated SPECT/CT for assessment of haemodynamically significant coronary artery lesions in patients with acute coronary syndrome

Purpose  

Early risk stratification in patients with non-ST elevation acute coronary syndromes (NSTE-ACS) is important since the benefit from more aggressive and costly treatment strategies is proportional to the risk of adverse clinical events. In the present study we assessed whether hybrid single photon emission computed tomography (SPECT)/coronary computed tomography angiography (CCTA) technology could be an appropriate tool in stratifying patients with NSTE-ACS.     

Diagnostic performance of multidetector CT angiography for assessment of coronary artery disease: meta-analysis

PURPOSE: To review the literature on the diagnostic performance of multidetector computed tomographic (CT) angiography for assessment of symptomatic coronary artery disease, with conventional coronary angiography as the reference standard. MATERIALS AND METHODS: A PubMed and manual search of the literature published between January 1998 and May 2006 on use of multidetector CT angiography compared with coronary angiography in patients with symptomatic coronary artery disease was performed. Summary estimates of diagnostic odds ratio, sensitivity, and specificity were calculated. Random-effects models were used to compare the diagnostic performance of four-, 16-, and 64-detector CT angiographic units, and the proportion of nonassessable coronary arterial segments was evaluated. RESULTS: Fifty-four studies were included in the meta-analysis: 22 studies with four-detector CT angiography, 26 with 16-detector CT angiography, and six with 64-detector CT angiography. The pooled sensitivity and specificity for detecting a greater than 50% stenosis per segment were 0.93 (95% confidence interval [CI]: 0.88, 0.97) and 0.96 (95% CI: 0.96, 0.97) for 64-detector CT angiography, 0.83 (95% CI: 0.76, 0.90) and 0.96 (95% CI: 0.95, 0.97) for 16-detector CT angiography, and 0.84 (95% CI: 0.81, 0.88) and 0.93 (95% CI: 0.91, 0.95) for four-detector CT angiography, respectively. Results of regression analysis indicated that the diagnostic performance significantly improved with the newer generations of multidetector CT scanners (64- and 16-detector vs four-detector units), adjusted for exclusion of nonassessable segments, and contrast agent concentration used (P < .05). Simultaneously, the nonassessable proportion of segments significantly decreased with the newer generations of multidetector CT scanners, adjusted for heart rate, prevalence of significant disease, and mean age. CONCLUSION: With the newer generations of multidetector CT scanners, the diagnostic performance for the assessment of coronary artery disease has significantly improved, and the proportion of nonassessable segments has decreased.     

Ultra-high-resolution CT angiography of the artery of Adamkiewicz: a feasibility study

Purpose

Preoperative identification of the artery of Adamkiewicz can help prevent postoperative spinal cord injury following thoracic and thoracoabdominal aortic repair. Several studies have demonstrated the feasibility of evaluating the artery of Adamkiewicz using multi-detector row computed tomography (CT), but precise visualization remains a challenge. The present study was conducted to evaluate the usefulness of ultra-high-resolution CT for visualizing the artery of Adamkiewicz with a slice thickness of 0.25 versus 0.5 mm in patients with aortic aneurysms.

Methods

Our institutional review board approved this study. Twenty-four patients with thoracic and thoracoabdominal aneurysms were scanned with beam collimation of 0.25 mm × 128. Images were reconstructed with slice thicknesses of 0.25 and 0.5 mm. The signal-to-noise ratio (SNR) of the aorta and contrast-to-noise ratio (CNR) between the anterior spinal artery and spinal cord were measured. Two independent observers evaluated visualization of the artery of Adamkiewicz and its continuity between the anterior spinal artery and the aorta using a four-point scale.

Results

No significant differences in the SNR of the aorta or CNR of the anterior spinal artery were observed between 0.25- and 0.5-mm slices. The average visualization score was significantly higher for 0.25-mm slices (3.58 ± 0.78) than for 0.5-mm slices (3.13 ± 0.99) (p = 0.01). The percentage of patients with nondiagnostic image quality was significantly lower for 0.25-mm slices (8.3%) than for 0.5-mm slices (33.3%) (p = 0.03).

Conclusion

In patients with aortic aneurysms, ultra-high-resolution CT with 0.25-mm slices significantly improves visualization of the artery of Adamkiewicz compared to 0.5-mm slices.

     

Virtual 3-D 18F-FDG PET/CT panendoscopy for assessment of the upper airways of head and neck cancer patients: a feasibility study

Purpose

The aim of this study was to evaluate whether a virtual 3-D ¹⁸F-fluorodeoxyglucose (FDG) positron emission tomography (PET)/CT panendoscopy is feasible and can be used for noninvasive imaging of the upper airways and pharyngeal/laryngeal tumours.

Methods

From ¹⁸F-FDG PET/CT data sets of 40 patients (29 men, 11 women; age 61?±?9?years) with pharyngeal or laryngeal malignancies virtual 3-D ¹⁸F-FDG PET/CT panendoscopies were reconstructed and the image processing time was measured. The feasibility of assessing the oral cavity, nasopharynx, tongue base, soft palate, pharyngeal tonsils, epiglottis, aryepiglottic folds, piriform sinus, postcricoid space, glottis, subglottis, trachea, bronchi and oesophagus and of detecting primary tumours was tested. Results of fibre-optic bronchoscopy and histology served as the reference standard.

Results

The nasopharynx, tongue base, soft palate, pharyngeal tonsils, epiglottis, subglottis and the tracheobronchial tree were accessible in all 40, and the aryepiglottic folds, posterior hypopharyngeal wall, postcricoid space, piriform sinus, glottis, oral cavity and oesophagus in 37, 37, 37, 37, 33, 16 and 0 patients, respectively. In all 12 patients with restricted fibre-optic evaluation due to being primarily intubated, the subglottis was accessible via virtual panendoscopy. The primary tumour was depicted in 36 of 40 patients (90?%). The mean processing time for virtual ¹⁸F-FDG PET/CT panendoscopies was 145?±?98?s.

Conclusion

Virtual ¹⁸F-FDG PET/CT panendoscopy of the upper airways is technically feasible and can detect pharyngeal and laryngeal malignancies. This new tool can aid in the complete evaluation of the subglottic space in intubated patients and may be used for planning optical panendoscopies, biopsies and surgery in the future.     

PET/CT in lymphoma: prospective study of enhanced full-dose PET/CT versus unenhanced low-dose PET/CT.

PET/CT combines functional and morphologic data and increases diagnostic accuracy in a variety of malignancies. This study prospectively compares the agreement between contrast-enhanced full-dose PET/CT and unenhanced low-dose PET/CT in lesion detection and initial staging of Hodgkin's disease and non-Hodgkin's lymphoma. METHODS: Forty-seven biopsy-proven lymphoma patients underwent a 18F-FDG PET/CT study that included unenhanced low-dose CT and enhanced full-dose CT for initial staging. Patients who had undergone previous diagnostic CT for initial staging were excluded. For every patient, each modality of PET/CT images was evaluated by either of 2 pairs of readers, with each pair comprising 1 experienced radiologist and 1 experienced nuclear physician. While evaluating one of the 2 types of PET/CT, the readers were unaware of the results of the other type. Lesion detection, number of sites affected in each anatomic region, and disease stage were assessed. Agreement between techniques was determined by the kappa-statistic, and discordances were studied by the McNemar test. Clinical, analytic, histopathologic, diagnostic CT, and PET data; data from other imaging techniques; and follow-up data constituted the reference standard. RESULTS: For region-based analysis, no significant differences were found between unenhanced low-dose PET/CT and contrast-enhanced full-dose PET/CT, although full-dose PET/CT showed fewer indeterminate findings and a higher number of extranodal sites affected than did low-dose PET/CT. Agreement between the 2 types of PET/CT was almost perfect for disease stage (kappa = 0.92; P < 0.001). CONCLUSION: Our study showed a good correlation between unenhanced low-dose PET/CT and contrast-enhanced full-dose PET/CT for lymph node and extranodal disease in lymphomas, suggesting that unenhanced low-dose PET/CT might suffice in most patients as the only imaging technique for the initial staging of lymphomas, reserving diagnostic CT for selected cases.     

CT of coronary artery disease

The socioeconomic importance of heart disease provides considerable motivation for development of radiologic tools for noninvasive imaging of the coronary arteries. Current computed tomographic (CT) techniques combine high speed and spatial resolution with sophisticated electrocardiographic synchronization and robustness of use. Application of these modalities for evaluation of coronary artery disease is a topic of active current research. Coronary artery calcium measurements with different CT techniques have been used for determining the risk of coronary events, but the exact role of this marker for cardiac risk stratification remains unclear pending results of population-based studies. Contrast material-enhanced CT coronary angiography has become an established clinical indication for some scenarios (eg, coronary artery anomalies, bypass patency, surgical planning). With current technology, the accuracy of CT coronary angiography for detection of coronary artery stenoses appears promising enough to warrant pursuit of this application, but sensitivity is still not high enough for routine diagnostic needs. The high negative predictive value of a normal CT coronary angiogram, however, may be useful for reliable exclusion of coronary artery stenosis. The cross-sectional nature of CT may allow noninvasive assessment of the coronary artery wall. Use of contrast-enhanced CT coronary angiography for detection, characterization, and quantification of atherosclerotic changes and total disease burden in coronary arteries as a potential tool for cardiac risk stratification is currently being investigated.     

Non-invasive assessment of coronary artery disease with CT coronary angiography and SPECT: a novel dose-saving fast-track algorithm

Purpose  

To validate a new low-dose and rapid stepwise individualized algorithm for non-invasive assessment of ischemic coronary artery disease by sequential use of prospectively ECG-triggered low-dose CT coronary angiography (CTCA) and low-dose single-photon emission computed tomography myocardial perfusion imaging (SPECT-MPI).     

Diagnostic pathway of integrated SPECT/CT for coronary artery disease

Treatment strategy in patients with suspected coronary artery disease (CAD) is driven by symptomatology in combination with diagnostic evaluation of the extent and/or severity of atherosclerosis in the coronary arteries and ischemia in the myocardium, i.e., the anatomic and functional correlates of CAD. Whereas multislice row computed tomography (MSCT) has the advantage of detecting coronary atherosclerosis at its earliest stages, thereby allowing initiation of appropriate therapeutic measures well before development of obstructive CAD, myocardial perfusion imaging (MPI) SPECT can clarify the hemodynamic consequences of the anatomic findings on MSCT based on a functional assessment of myocardial blood flow. There is a lack of correlation between coronary artery calcium (CAC), coronary artery stenosis, and MPI SPECT. Therefore CAC scoring and stress MPI should be thus considered complementary approaches rather than exclusionary in the evaluation of the patient at risk for CAD. The integration of anatomic and functional information may provide additional information for the clinician by the improved risk stratification and diagnostic accuracy of integrated techniques. The majority of previous studies are based on a sequential flowchart, starting with either SPECT or CAC scoring that finally directs the therapeutic strategy. Patients at low risk for CAD can be selected for primary prevention, and patients at high risk for CAD can be directly selected for coronary angiography (CAG). The remaining group of patients at intermediate risk for CAD can be substratified into lower- and higher-risk categories based on the presence or absence of stress-induced ischemia on MPI SPECT and CAC scoring. An integration of SPECT and CAC as a starting point for CAD detection in symptomatic patients at intermediate risk for CAD may facilitate a tailored diagnostic as well as therapeutic approach. Finally, using SPECT/CT, MPI SPECT, and CAC findings may be completed with CT angiography. The development of SPECT/CT hybrid systems is therefore of important value for the nuclear cardiology armamentarium. This editorial commentary outlines a diagnostic pathway of integrated SPECT/CT for CAD assessment in symptomatic patients at intermediate risk for CAD.     

SPECT and PET in the evaluation of coronary artery disease.

Cardiac positron emission tomography (PET) is an accurate method for assessing myocardial perfusion and metabolism in the evaluation of coronary heart disease. PET allows more accurate detection of myocardial ischemia than single photon emission tomography (SPECT). In addition, PET has higher spatial resolution and allows attenuation correction and the quantification of various physiologic parameters. PET with 2-(fluorine-18) fluoro-2-deoxy-D-glucose is considered the standard of reference for predicting improvement in regional or global left ventricular function after revascularization by identifying hibernating viable myocardium that shows diminished perfusion and preserved metabolism. Other less commonly used clinical applications of cardiac PET include assessment of myocardial oxygen consumption and fatty acid metabolism. The use of PET in myocardial imaging is expected to increase in the near future with the regional distribution of positron-emitting radiotracers and the emergence of relatively low-cost PET systems.     

The utility of cardiac CT beyond the assessment of suspected coronary artery disease

Extensive work has been done over recent years to improve the spatial and temporal resolution of electrocardiogram (ECG)-gated cardiac computed tomography (CT). Advances in both hardware and software analysis have enabled the development of non-invasive coronary angiography. However, these high-quality examinations lend themselves to multiple additional applications beyond coronary angiography. In this review, we illustrate and discuss some established and some emerging applications of ECG-gated cardiac CT beyond the assessment of suspected coronary disease, particularly in light of recent recommendations on the appropriate use of this technology.