Hendrik Everaert

Interest of the ordered subsets expectation maximization (OS-EM) algorithm in pinhole single-photon emission tomography reconstruction : A phantom study

Abstract.Pinhole single-photon emission tomography (SPET) has been proposed to improve the trade-off between sensitivity and resolution for small organs located in close proximity to the pinhole aperture. This technique is hampered by artefacts in the non-central slices. These artefacts are caused by truncation and by the fact that the pinhole SPET data collected in a circular orbit do not contain sufficient information for exact reconstruction. The ordered subsets expectation maximization (OS-EM) algorithm is a potential solution to these problems. In this study a three-dimensional OS-EM algorithm was implemented for data acquired on a single-head gamma camera equipped with a pinhole collimator (PH OS-EM). The aim of this study was to compare the PH OS-EM algorithm with the filtered back-projection algorithm of Feldkamp, Davis and Kress (FDK)and with the conventional parallel-hole geometry as a whole,using a line source phantom, Picker’s thyroid phantom and a phantom mimicking the human cervical column. Correction for the angular dependency of the sensitivity in the pinhole geometrywas based on a uniform flood acquisition. The projection data were shifted according to the measured centre of rotation. No correction was made for attenuation, scatter or distance-dependent camera resolution. The resolution measured with the line source phantom showed a significant improvement with PH OS-EM as compared with FDK, especially in the axial direction. Using Picker’s thyroid phantom, one iteration with eight subsets was sufficient to obtain images with similar noise levels in uniform regions of interest to those obtained with the FDK algorithm. With these parameters the reconstruction time was 2.5 times longer than for the FDK method. Furthermore, there was a reduction in the artefacts caused by the circular orbit SPET acquisition. The images obtained from the phantom mimicking the human cervical column indicated that the improvement in image quality with PH OS-EM is relevant for future clinical useand that the improvements obtained using the OS-EM algorithm are more significant for the pinhole geometry than for the conventional parallel-hole geometry. We conclude that PH OS-EM is a practical and promising alternative for pinhole SPET reconstruction.

Left ventricular ejection fraction from gated SPET myocardial perfusion studies: a method based on the radial distribution of count rate density across the myocardial wall

Left ventricular ejection fraction (LVEF) can be derived from gated single-photon emission tomographic (SPET) myocardial perfusion studies using either manual or edge detection techniques. In the presence of severe perfusion defects, however, difficulties may be encountered. In this article a method based on the assumption that the average position of the myocardial wall can be localized by means of statistical analysis of the distribution count density, and not on edge detection, is used to measure LVEF. SPET myocardial perfusion images, gated in eight time bins, were recorded in 50 patients 60 min after the injection of 925 MBq technetium-99m tetrofosmin. Masking of non-myocardial structures and thresholding resulted in images in which only myocardial walls had significant non-zero values. The distance of the wall relative to the centre of the cavity was calculated in the three-dimentional space as the first moment of the count rate distribution along radii originating in the centre of the cavity. LVEF was calculated using, for each time bin, the sum of the cube of all distances as an estimate of the cavity volume. The method required minimal operator interventions and was successful in all patients, including those with severe perfusion defects. Intraobserver and interobserver variability was excellent, with regression coefficients of 0.97 and standard deviations of 4.5% and 4.7%, respectively. For 30 patients, the measurements were validated against planar equilibrium radionuclide angiography (ERNA) that was obtained within an interval of 1 week. LVEF ranged from 12% to 88%. Agreement between the two methods was excellent (LVEFEERNA=1.05+0.92 LVEFGSPET,r=0.93,P=0.023, SEE=7.06). The Bland-Altman analysis did not show any apparent trend in the differences between ERNA and gated SPET over a wide range of ejection fractions. The standard deviation of the differences was 3.1%. In addition no relationship was found between the two methods and the severity of perfusion defects. In conclusion, accurate measurements of LVEF are obtained from gated SPET perfusion images using a method based on statistical analysis of the count rate density. This method did not deteriorate even in the presence of severe perfusion defects and could therefore be used in following patients after myocardial infarction.

Low-dose dobutamine gated single-photon emission tomography : comparison with stress echocardiography

Abstract.Perfusion scintigraphy provides important information regarding the presence of viable tissue after myocardial infarction. Defects of moderate severity, however, may represent viable myocardium, necrotic tissue or a mixture of both. In this study the presence or absence of inotropic response in the infarcted area was assessed by low-dose dobutamine tetrofosmin gated single-photon emission tomography (LDD gated SPET). Results were compared with those obtained with stress echocardiography (SE). Twenty-five patients with acute myocardial infarction were studied. Gated SPET myocardial perfusion imaging was performed 60 min after the injection of technetium-99m tetrofosmin (925 MBq) at rest using a triple-headed camera equipped with focussing collimators (Cardiofocal). Two consecutive acquisitions were performed according to a ”fast” gated SPET protocol (3×20 stops, 9 s/stop, 64×64 pixel matrix, zoom 1.23) with the subjects remaining in the same position. The first acquisition was obtained at rest; the second acquisition was obtained under infusion of 10 µg kg–1 min–1 dobutamine. The severity of regional dysfunction, wall thickening severity (WTsev), was assessed and quantified using a method based on circumferential profile analysis. SE was performed at rest and during infusion of 5 and 10 µg kg–1 min–1 dobutamine. Two patients could not be analysed because of disturbing gastro-intestinal activity on the perfusion study. Under dobutamine 11 patients presented a significant change in WTsev (three showed normalisation, five an improvement and three a deterioration), while in 12 patients the WTsev score remained unchanged. The overall concordance between LDD gated SPET and SE was 83%. In patients with perfusion defects of moderate severity the concordance was 90% (9/10). It may be concluded that functional changes in infarcted areas induced by dobutamine can be detected with gated SPET. Good agreement was observed between LDD gated SPET and SE for the identification of inotropic reserve in infarcted areas.

Phase II study of helical tomotherapy for oligometastatic colorectal cancer

BACKGROUND To evaluate the efficacy and toxicity of helical tomotherapy in the treatment of oligometastatic colorectal cancer (CRC) patients who were not amenable for metastasectomy and/or (further) systemic treatment. PATIENTS AND METHODS CRC patients with five or less metastases were enrolled. No limitations concerning dimension or localization of the metastases were imposed. Patients were treated with intensity-modulated and image-guided radiotherapy using helical tomotherapy, delivering a total dose of 40 Gy in fractions of 4 Gy. Positron emission tomography-computed tomography (PET-CT) was carried out at baseline and 3 months after the initiation of radiotherapy to evaluate the metabolic response rate according to PET Response Criteria in Solid Tumors (PERCIST) version 1.0. Side-effects were scored using National Cancer Institute Common Terminology Criteria for Adverse Events (NCI-CTC AE) version 3.0. RESULTS Twenty-three patients were enrolled. A total of 52 metastases were treated. One patient (4%) experienced grade 3 vomiting; two patients (9%) grade 2 diarrhea and dysphagia, respectively. Twenty-two patients were evaluated by post-treatment PET-CT. Five (23%) and seven patients (32%) achieved a complete and partial metabolic response, respectively, resulting in an overall metabolic response rate of 55%. The actuarial 1-year local control, progression-free survival, and overall survival were 54%, 25% and 86%, respectively. CONCLUSION The use of helical tomotherapy in oligometastatic CRC patients resulted in a promising metabolic response rate of 55%.

Effects of low-dose dobutamine on left ventricular function in normal subjects as assessed by gated single-photon emission tomography myocardial perfusion studies

Abstract. Electrocardiography gated single-photon emission tomography (gated SPET) allows the assessment of regional perfusion and function simultaneously and in full spatial congruency. In this study changes in global and regional left ventricular function in response to dobutamine infusion were assessed in ten healthy volunteers using sequential gated SPET myocardial perfusion acquisitions. Four consecutive gated SPET images were recorded 60 min after injection of 925 MBq technetium-99m tetrofosmin on a three-head camera equipped with focussing collimators. Two acquisitions were made at rest (baseline 1 and 2), and the third and fourth acquisitions were started 5 min after the beginning of the infusion of 5 and 10 µg kg–1 min–1 dobutamine, respectively. Systolic wall thickening (WT) was quantified using a method based on circumferential profile analysis. Left ventricular ejection fraction (LVEF) and volumes were calculated automatically using the Cedars-Sinai program. Nine of the ten subjects presented a definite increase in WT during dobutamine infusion. WT increased on average from 46%±14% at baseline to 71%±23% (range: 37%–106%; P<0.05) during 5 µg kg–1 min–1 dobutamine infusion and to 85%±25% (range: 62%–123%; P<0.05 with respect to WT at 5 µg kg–1 min–1) during 10 µg kg–1 min–1 dobutamine infusion. Apical segments showed the largest WT at baseline. The average WT response to dobutamine was similar for all parts of the myocardium. It is concluded that changes in WT induced by infusion of low-dose dobutamine can be assessed by sequential gated SPET myocardial perfusion studies. The ”stress gated SPET” protocol proposed in this study might be helpful to distinguish viable from scar tissue in patients with coronary artery disease, by demonstrating a preserved inotropic response in hypoperfused myocardium.

Cardiofocal collimators for gated single-photon emission tomographic myocardial perfusion imaging.

Abstract. Cardiofocal collimators (CFCs) are more sensitive than parallel-hole collimators (PHCs) of the same resolution because the rays converge in the centre of the field of view. After reconstruction a useful field of view with a 10 cm radius in which both sensitivity and resolution are homogeneous is obtained. In this article the feasibility and accuracy of gated single-photon emission tomographic (gated SPET) myocardial perfusion imaging using a triple-head camera equipped with CFC, is evaluated. Twenty patients with a history of myocardial infarction were studied. SPET myocardial perfusion images, gated in eight time bins, were acquired in a random sequence with a PHC and a CFC for each patient. Imaging was started 60 min after the injection of 925 MBq of technetium-99m tetrofosmin at rest. Ninety-six projections over 360° were acquired, with 32 stops of 40 s for the PHC and 20 s for the CFC in order to obtain similar count densities. The extent (EXT) and severity (SEV) of perfusion defects were quantified on polar maps using the non-gated data. Left ventricular volumes [end-diastolic volume (EDV), end-systolic volume (ESV)] and ejection fraction (LVEF) were calculated from gated data using the Cedars-Sinai program. In 17 of 20 patients the complete left ventricle was positioned within the useful field of view of the CFC. The results in respect of perfusion, volumes and ejection fraction were almost identical to those obtained with the PHC. The mean difference±SD between the CFC and the PHC was −2.30±7.16 (% of LV area) for EXT, −0.48±2.90 for SEV (arbitrary units), −1,50±5.25 (ml) for EDV and 0.53±4.10 (%) for LVEF. The largest differences in EXT and LV volumes were observed in patients in whom a part of the LV was not positioned within the useful field of view. We conclude that, for the majority of patients, identical information with regard to both perfusion and function can be derived from gated SPET myocardial perfusion studies obtained with PHCs or with CFCs. Because of the greater sensitivity, however, a much shorter acquisition time is required with CFCs.

Effect of beta-blockade on low-dose dobutamine-induced changes in left ventricular function in healthy volunteers: assessment by gated SPET myocardial perfusion scintigraphy

Abstract.Viability studies are often performed in patients receiving beta-blocking agents. However, the intake of beta-blocking agents could influence the identification of viable myocardium when low-dose dobutamine is used to demonstrate inotropic reserve. The aim of this study was to quantify the effect of beta-blockade on global and regional left ventricular function in healthy volunteers using low-dose dobutamine gated single-photon emission tomographic (SPET) myocardial perfusion scintigraphy. Ten subjects were studied once ”on” and once ”off” beta-blocker therapy (metoprolol succinate, 100 mg day–1). On each occasion four consecutive gated SPET acquisitions (of 7 min duration) were recorded after injection of 925 MBq technetium-99m tetrofosmin on a triple-headed camera equipped with focussing (Cardiofocal) collimators. Acquisitions were made at rest (baseline 1 and 2) and 5 min after the beginning of the infusion of 5 and 10 µg kg–1 min–1 dobutamine. Wall thickening (WT) was quantified using a method based on circumferential profile analysis. Left ventricular ejection fraction (LVEF) was obtained using the Cedars-Sinai algorithm. Blood pressure (BP) and heart rate (HR) were recorded at the end of each acquisition. At baseline LVEF, WT and systolic BP values under beta-blockade were not significantly different from those obtained in the non-beta-blocked state. The mean HR and diastolic BP at baseline were lower under beta-blockade. Dobutamine administration (at 5 and 10 µg kg–1 min–1) induced a significant increase in WT, LVEF and systolic BP in all subjects both on and off beta-blockade. The increases in WT, LVEF and systolic BP in the beta-blocked state were less pronounced but not significantly different. HR increased significantly at 10 µg kg–1 min–1 dobutamine without beta-blocker administration, while no increase in HR was observed in the beta-blocked state. Beta-blocker therapy in healthy subjects attenuates the inotropic and chronotropic myocardial response to low-dose dobutamine. At doses of 5 and 10 µg kg–1 min–1 dobutamine, however, significant increases in global and regional left ventricular function can still be measured using consecutive gated SPET myocardial perfusion scintigraphy acquisitions even under beta-blocker therapy.

PET and CT demonstration of metastatic invasion of the thoracic duct.

Both FDG-PET and multislice CT are valuable tools in the follow-up of patients with colorectal carcinoma, serving to demonstrate locoregional recurrence and generalised disease [1–3]. Metastatic spread to distant sites frequently affects the liver, adrenal glands and lungs [3]. Some reports have described metastatic involvement of mediastinal lymph nodes [4]. Here we present a case of metastatic spread to the thoracic duct and supraclavicular lymph nodes detected by FDG-PET and multi-slice CT (MSCT) in a patient with a history of sigmoid cancer. Part a of the figure shows a maximal intensity projection (anterior view) of the FDG distribution in a 54-year-old female who presented with bilateral swelling in the subclavicular regions 4 years after resection of a welldifferentiated adenocarcinoma of the sigmoid followed by chemotherapy and irradiation. Intense tracer accumulation with a linear distribution can be seen in the upper abdomen, the mediastinum and the base of the neck bilaterally. Also shown are the corresponding CT (b) and FDG-PET (c) images of transverse sections taken at the level of the clavicle (b1 and c1), the carina (b2 and c2) and the lower mediastinum (b3 and c3). On MSCT the thoracic duct (solid arrow) is demonstrated as a longitidunal mass between the oesophagus (dotted arrow) and the azygos vein (dashed arrow). A normal thoracic duct has an average diameter of 1.3 mm [5] and appears as a small dotlike density at the anterior and, usually, the medial aspect of the azygos vein [6]. Corresponding FDG-PET slices demonstrate an intense hypermetabolic lesion in the posterior mediastinum and subclavicular regions, corresponding to the enlarged thoracic duct and confirming tumoural invasion.

EP-1084 PHASE II STUDY OF HELICAL TOMOTHERAPY IN THE MULTIDISCIPLINARY TREATMENT OF OLIGOMETASTATIC COLORECTAL CANCER

653 Background: Complete metastasectomy provides a real chance for long-term survival in patients with oligometastatic colorectal cancer (CRC). For patients who are not amenable for metastasectomy, we demonstrated in a previous study the feasibility of moderately hypofractionated intensity-modulated and image-guided radiotherapy (RT) by helical tomotherapy. Aiming at higher response rates, we evaluated in this study helical tomotherapy delivering 50 Gy in daily fractions of 5 Gy. METHODS Inoperable CRC patients with ≤ 5 metastases were enrolled. No limitations concerning dimension or localization of the metastases were imposed. Whole body PET-CT was performed at baseline and 3 months after the initiation of RT to evaluate the metabolic response rate according to PERCIST v 1.0. Side effects were scored using the NCI CTC AE v 3.0 scale. RESULTS We report the results of the first 22 patients. Thirteen patients (59%) received previous chemotherapy for metastatic disease, displaying residual (n=7) or progressive (n=6) metabolic active metastatic disease at time of inclusion. A total of 51 metastases were treated. Most common sites were the lung, liver and lymphnodes. One patient (5%) experienced grade 3 dysphagia; 2 patients (9%) and 1 patient (5%) grade 2 dysphagia and diarrhea, respectively. Twenty patients were evaluated by post-treatment PET-CT. Five and 6 patients achieved a complete and partial metabolic response, resulting in an overall metabolic response rate of 55%. At a median follow-up of 11 months, 17 patients (77%) developed progressive disease, of which 3 isolated local progression. Five patients (23%) are in remission in all irradiated areas without evidence of distant recurrence. Interestingly, those 5 patients received previous chemotherapy with residual oligometastatic disease at time of inclusion. CONCLUSIONS Ten fractions of 5 Gy resulted in a promising 55% metabolic response rate with limited toxicity. Helical tomotherapy is an attractive modality in the multidisciplinary approach of oligometastatic CRC, more specifically in the consolidation of residual and inoperable oligometastatic disease in patients previously treated with chemotherapy.

Complete right-to-left shunt on lung perfusion SPECT results in the detection of a persistent left vena cava superior draining to the left atrium

In order to exclude acute pulmonary embolism, a lung perfusion scintigraphy was performed in a 53-year-old male, with a history of Fallot’s tetralogy. He had been immobilized because of a tibial fracture and complained of worsening chest pain and dyspnea.