RESUMEN
OBJECTIVE: Respiratory motion is a potential cause of artefact and downgrading the quality of ECG-gated single photon emission computed tomography (SPECT) images that may result in clinical misinterpretation. We studied qualitatively the effects of respiratory motion on gated SPECT myocardial perfusion and function using Monte Carlo simulated data. METHODS: NCAT phantom was used to model a human torso. The cardiac and respiratory cycles of torso were 1 and 5 s, respectively. Eight realizations of the phantom, having diaphragmatic motion amplitudes of 0-7 cm were generated. SimSET Monte Carol simulator was used to image the phantom and generate gated studies of 16 frames per cardiac cycle. RESULTS: Our results demonstrated the underestimation of left ventricle end-diastolic, end-systolic, stroke volumes and ejection fraction and overestimation of wall motion and wall thickening (p < 0.01). In addition, the mean percentage of count in the basal-inferior, mid-inferior, apical-inferior, basal-septal and mid-septal segments were significantly lower due to respiratory motion when compared with control (p < 0.01). The changes in uptake were not significant in the apex, antroapical, apicoseptal, apicolateral, mid-anterior, basal-anterior, mid-lateral and basal-lateral segments. CONCLUSION: Respiratory motion has significant effect on the calculation of the left ventricular functional and regional myocardial perfusion in the GSPECT. The amount of deterioration and quality distortion of the images depends on the amplitude of the diaphragmatic motion.
Asunto(s)
Tomografía Computarizada por Emisión de Fotón Único Sincronizada Cardíaca/métodos , Modelos Biológicos , Movimiento , Respiración , Ventrículos Cardíacos/diagnóstico por imagen , Humanos , Masculino , Método de Montecarlo , Fantasmas de Imagen , Volumen Sistólico , Función Ventricular IzquierdaRESUMEN
OBJECTIVE: Gated myocardial perfusion single-photon emission computed tomography (GSPECT) has been established as an accurate and reproducible diagnostic and prognostic technique for the assessment of myocardial perfusion and function. Respiratory motion is among the major factors that may affect the quality of myocardial perfusion imaging (MPI) and consequently the accuracy of the examination. In this study, we have proposed a new approach for the tracking of respiratory motion and the correction of unwanted respiratory motion by the use of respiratory-cardiac gated-SPECT (RC-GSPECT). In addition, we have evaluated the use of RC-GSPECT for quantitative and visual assessment of myocardial perfusion and function. MATERIALS AND METHODS: Twenty-six patients with known or suspected coronary artery disease (CAD)-underwent two-day stress and rest (99m)Tc-Tetrofosmin myocardial scintigraphy using both conventional GSPECT and RC-GSPECT methods. The respiratory signals were induced by use of a CT real-time position management (RPM) respiratory gating interface. A PIO-D144 card, which is transistor-transistor logic (TTL) compatible, was used as the input interface for simultaneous detection of both ECG and respiration signals. RESULTS: A total of 26 patients with known or suspected CAD were examined in this study. Stress and rest myocardial respiratory motion in the vertical direction was 8.8-16.6 mm (mean, 12.4 +/- 2.9 mm) and 7.8-11.8 mm (mean, 9.5 +/- 1.6 mm), respectively. The percentages of tracer intensity in the inferior, inferoseptal and septal walls as well as the inferior to lateral (I/L) uptake ratio was significantly higher with the use of RC-GSPECT as compared to the use of GSPECT (p < 0.01). In a left ventricular ejection fraction (LVEF) correlation analysis between the use of rest GSPECT and RC-GSPECT with echocardiography, better correlation was noted between RC-GSPECT and echocardiography as compared with the use of GSPECT (y = 0.9654x + 1.6514; r = 0.93, p < 0.001 versus y = 0.8046x + 5.1704; r = 0.89, p < 0.001). Nineteen (19/26) patients (73.1%) showed abnormal myocardial perfusion scans with reversible regional myocardial defects; of the 19 patients, 14 (14/26) patients underwent coronary angiography. CONCLUSION: Respiratory induced motion can be successfully corrected simultaneously with the use of ECG-gated SPECT in MPI studies using this proposed technique. Moreover, the use of ECG-gated SPECT improved image quality, especially in the inferior and septal regions that are mostly affected by diaphragmatic attenuation. However, the effect of respiratory correction depends mainly on the patient respiratory pattern and may be clinically relevant in certain cases.
Asunto(s)
Tomografía Computarizada por Emisión de Fotón Único Sincronizada Cardíaca/métodos , Circulación Coronaria , Respiración , Anciano , Enfermedad de la Arteria Coronaria/diagnóstico por imagen , Electrocardiografía , Femenino , Humanos , Masculino , Persona de Mediana Edad , Compuestos Organofosforados , Compuestos de Organotecnecio , RadiofármacosRESUMEN
Radiotherapy represents the most widely spread technique to control and treat cancer. To increase the treatment efficiency, high energy linacs are used. However, applying high energy photon beams leads to a non-negligible dose of neutrons contaminating therapeutic beams. In addition, using conventional linacs necessitates applying wedge filters in some clinical conditions. However, there is not enough information on the effect of these filters on the photoneutrons produced. The aim of this study was to investigate the change of photoneutron dose equivalent due to the use of linac wedge filters. A high energy (18 MV) linear accelerator (Elekta SL 75/25) was studied. Polycarbonate films were used to measure the dose equivalent of photoneutrons. After electrochemical etching of the films, the neutron dose equivalent was calculated using Hp(10) factor, and its variation on the patient plane at 0, 5, 10, 50 and 100 cm from the center of the X-ray beam was determined. By increasing the distance from the center of the X-ray beam towards the periphery, the photoneutron dose equivalent decreased rapidly for the open and wedged fields. Increasing of the field size increased the photoneutron dose equivalent. The use of wedge filter increased the proportion of the neutron dose equivalent. The increase can be accounted for by the selective absorption of the high energy photons by the wedge filter.
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Neutrones , Aceleradores de Partículas , PolímerosRESUMEN
High-energy linear accelerators (linacs) have several advantages, including low skin doses and high dose rates at deep-seated tumours. But, at energies more than 8 MeV, photonuclear reactions produce neutron contamination around the therapeutic beam, which may induce secondary malignancies. In spite of improvements achieved in medical linac designs, many countries still use conventional (non-intensity-modulated radiotherapy) linacs. Hence, in these conventional machines, fitting the beam over the treatment volume may require using blocks. Therefore, the effect of these devices on neutron production of linacs needs to be studied. The aim of this study was to investigate the effect of field shaping blocks on photoneutron dose in the treatment plane for two high-energy medical linacs. Two medical linacs, a Saturn 43 (25 MeV) and an Elekta SL 75/25 (18 MeV), were studied. Polycarbonate (PC) films were used to measure the fluence of photoneutrons produced by these linacs. After electrochemical etching of the PC films, the neutron dose equivalent was calculated at the isocentre and 50 cm away from the isocentre. It was noted that by increasing the distance from the centre of the X-ray beam towards the periphery, the photoneutron dose equivalent decreases rapidly for both the open and blocked fields. Increasing the energy of the photons causes an increase in the amount of photoneutron dose equivalent. At 25 MeV photon energy, the lead blocks cause a meaningful increase in the dose equivalent of photoneutrons. In this research, a 30% increase was seen in neutron dose contribution to central axis dose at the isocentre of a 25 MeV irregular field shaped by lead blocks. It is concluded that lead blocks must be considered as a source of photoneutron production when treating irregular fields with high-energy photons.