Simona Ben-Haim

Initial multicentre experience of high-speed myocardial perfusion imaging: comparison between high-speed and conventional single-photon emission computed tomography with angiographic validation

PurposeHigh-speed (HS) single-photon emission computed tomography (SPECT) with a recently developed solid-state camera shows comparable myocardial perfusion abnormalities to those seen in conventional SPECT. We aimed to compare HS and conventional SPECT images from multiple centres with coronary angiographic findings.MethodsThe study included 50 patients who had sequential conventional SPECT and HS SPECT myocardial perfusion studies and coronary angiography within 3xa0months. Stress and rest perfusion images were visually analysed and scored semiquantitatively using a 17-segment model by two experienced blinded readers. Global and coronary territorial summed stress scores (SSS) and summed rest scores (SRS) were calculated. Global SSS ≥3 or coronary territorial SSS ≥2 was considered abnormal. In addition the total perfusion deficit (TPD) was automatically derived. TPD >5xa0% and coronary territorial TPD ≥3xa0% were defined as abnormal. Coronary angiograms were analysed for site and severity of coronary stenosis; ≥50xa0% was considered significant.ResultsOf the 50 patients, 13 (26xa0%) had no stenosis, 22 (44xa0%) had single-vessel disease, 6 (12xa0%) had double-vessel disease and 9 (18xa0%) had triple-vessel disease. There was a good linear correlation between the visual global SSS and SRS (Spearman’s ρ 0.897 and 0.866, respectively; pu2009<u20090.001). In relation to coronary angiography, the sensitivities, specificities and accuracies of HS SPECT and conventional SPECT by visual assessment were 92xa0% (35/38), 83xa0% (10/12) and 90xa0% (45/50) vs. 84xa0% (32/38), 50xa0% (6/12) and 76xa0% (38/50), respectively (pu2009<u20090.001). The sensitivities, specificities and accuracies of HS SPECT and conventional SPECT in relation to automated TPD assessment were 89xa0% (31/35), 57xa0% (8/14) and 80xa0% (39/49) vs. 86xa0% (31/36), 77xa0% (10/13) and 84xa0% (41/49), respectively.ConclusionHS SPECT allows fast acquisition of myocardial perfusion images that correlate well with angiographic findings with overall accuracy by visual assessment better than conventional SPECT. Further assessment in a larger patient population may be needed to confirm this observation.

Dynamic SPECT: evolution of a widely available tool for the assessment of coronary flow reserve

Myocardial perfusion imaging (MPI) SPECT is well established in the diagnosis, monitoring response to treatment and risk stratification in patients with known or suspected coronary artery disease (CAD). PET enables quantitative assessment of myocardial blood flow (MBF, in millilitres per gram per minute) and coronary flow reserve (CFR), and quantification with O-water, N-ammonia and recently Rb has been validated over a wide range of blood flows in animal models and humans [1–4]. Quantitative assessment of MBF has been shown to improve the diagnostic accuracy of conventional MPI with SPECT or PET, to improve cardiac risk assessment and to predict outcome [5–7]. Quantitation of MBF enables absolute assessment of myocardial flow and vasodilator reserve without the assumption of a normal reference region [8]. Therefore, the limitation of conventional MPI (underestimation of the extent and severity of multivessel CAD, when tracer uptake in the best-perfused myocardial region does not represent normally perfused myocardium) can be overcome by the use of absolute quantitation [9]. Whereas PET is very costly and complex, SPECT systems are widely used for the assessment of myocardial perfusion in patients for the diagnosis and management of CAD. However, quantitative assessment with SPECT has been limited. To enable quantitation with SPECT a multidetector system is required to permit fast acquisition of dynamic data in 5 – 10 s, and a suitable SPECT tracer is necessary. Transmission imaging for attenuation correction will allow accurate quantitation. Quantification of myocardial perfusion reserve has been attempted using SPECT and Tl in dogs [10] and Tc-labelled tracers [10–12]. Dynamic SPECT imaging using multidetector SPECT systems and kinetic modelling of Tc-teboroxime has shown good correlation with microsphere-determined blood flow. However, limitations in detector sensitivity and temporal resolution of conventional SPECT systems prohibit further assessment [10, 11]. Another SPECT technique based on first-pass planar imaging followed by conventional SPECTMPI has been used to estimate a retention index of MBF and CFR [12]. This technique has shown a generally good correlation with PETmeasured flow, but CFR is underestimated at high flow rates [13]. The use of a retention index to estimate CFR using this method compared to absolute MBF from PET results in an underestimation of CFR values in the SPECT-based technique, since tracer retention decreases with increasing blood flow [14]. Spatial and timing resolution are poorer with SPECT and the tracer retention index underestimates CFR compared to quantitative PET. SPECT is indeed simpler than PET but this technique, unlike PET, does not include dynamic acquisition of tomographic data. In addition, the technique works only for tracers that act like microspheres, showing a constant extraction over a large range of flow rates and showing no washout from the time of injection to the time of measurement. Conventional SPECT systems are limited in the dynamic collection of tomographic data. These systems consist of slowly rotating cameras with large detectors. The detectors’ orbit is limited by mechanical as well as safety factors and the angular projections obtained are inconsistent, resulting in blurred images and possible bias in the estimated kinetic parameters. In addition, conventional detector crystals suffer S. Ben-Haim Institute of Nuclear Medicine, University College London, University College Hospital, London, UK

Feasibility study of a novel general purpose CZT-based digital SPECT camera: initial clinical results

BackgroundThe performance of a prototype novel digital single-photon emission computed tomography (SPECT) camera with multiple pixelated CZT detectors and high sensitivity collimators (Digital SPECT; Valiance X12 prototype, Molecular Dynamics) was evaluated in various clinical settings.Images obtained in the prototype system were compared to images from an analog camera fitted with high-resolution collimators. Clinical feasibility, image quality, and diagnostic performance of the prototype were evaluated in 36 SPECT studies in 35 patients including bone (nu2009=u200921), brain (nu2009=u20095), lung perfusion (nu2009=u20093), and parathyroid (nu2009=u20093) and one study each of sentinel node and labeled white blood cells. Images were graded on a scale of 1–4 for sharpness, contrast, overall quality, and diagnostic confidence.ResultsDigital CZT SPECT provided a statistically significant improvement in sharpness and contrast in clinical cases (mean score of 3.79u2009±u20090.61 vs. 3.26u2009±u20090.50 and 3.92u2009±u20090.29 vs. 3.34u2009±u20090.47 respectively, pu2009<u20090.001 for both). Overall image quality was slightly higher for the digital SPECT but not statistically significant (3.74 vs. 3.66).ConclusionCZT SPECT provided significantly improved image sharpness and contrast compared to the analog system in the clinical settings evaluated. Further studies will evaluate the diagnostic performance of the system in large patient cohorts in additional clinical settings.

Erratum to: Performance of cardiac cadmium-zinc-telluride gamma camera imaging in coronary artery disease: a review from the cardiovascular committee of the European Association of Nuclear Medicine (EANM)

The trade-off between resolution and count sensitivity dominates the performance of standard gamma cameras and dictates the need for relatively high doses of radioactivity of the used radiopharmaceuticals in order to limit image acquisition duration. The introduction of cadmium-zinc-telluride (CZT)-based cameras may overcome some of the limitations against conventional gamma cameras. CZT cameras used for the evaluation of myocardial perfusion have been shown to have a higher count sensitivity compared to conventional single photon emission computed tomography (SPECT) techniques. CZT image quality is further improved by the development of a dedicated three-dimensional iterative reconstruction algorithm, based on maximum likelihood expectation maximization (MLEM), which corrects for the loss in spatial resolution due to line response function of the collimator. All these innovations significantly reduce imaging time and result in a lower patients radiation exposure compared with standard SPECT. To guide current and possible future users of the CZT technique for myocardial perfusion imaging, the Cardiovascular Committee of the European Association of Nuclear Medicine, starting from the experience of its members, has decided to examine the current literature regarding procedures and clinical data on CZT cameras. The committee hereby aims 1) to identify the main acquisitions protocols; 2) to evaluate the diagnostic and prognostic value of CZT derived myocardial perfusion, and finally 3) to determine the impact of CZT on radiation exposure.

Lung and Mediastinal Tumors

Lung cancer accounts for 15% of all cancers in the USA and is the leading cause of cancer death. Non-small cell cancers (NSCLC), including squamous cell, adenocarcinoma, and large cell carcinomas account for 85% of lung cancers. Cigarette smoking is linked to the majority of lung cancers. Staging of lung cancer uses the American joint cancer committee (AJCC) TNM classification. CT is the modality of choice for lung cancer detection, and identifying adrenal involvement. Because of the low specificity of CT for characterizing lung nodules (lesions 1 cm concentrate [18F]FDG. However false-positive scans can occur because inflammatory lesions such as sarcoid or tuberculosis also concentrate [18F]FDG. False-negative scans can occur due to small lesion size or malignancies such as bronchiolo-alveolar carcinoma (BAC) or carcinoid. Pretreatment [18F]FDG PET/CT provides prognostic information since there is a relationship between SUV of the tumor and outcome. CT allows accurate differentiation of potentially resectable T1–T3 lesions from unresectable T4 tumors. Contrast CT is used for N staging and the most widely used diagnostic criterion of nodal metastases is a measurement of lymph node size. [18F]FDG imaging has better sensitivity and specificity than CT, with an NPV above 90% for the detection of metastatic mediastinal nodes. In patients treated with radiation, post-radiation pneumonitis and fibrosis may be difficult to distinguish from tumor recurrence on CT. Magnetic resonance imaging (MRI) and [18F]FDG-PET/CT can be helpful to make this distinction. In small cell lung cancer (SCLC), [18F]FDG imaging is useful for detection and staging. Moreover, [18F]FDG can also assess response to chemotherapy as early as the end of the first cycle. SUV of the primary lesion is a significant prognostic factor.