RESUMEN
A dual-head scintillation camera has been adapted for high-energy (511-keV) imaging by extending the useful energy range and linearity maps to 560 keV, implementing high-energy sensitivity maps, and developing high-energy collimators. High-energy parallel-hole collimators have inferior spatial resolution and sensitivity relative to the low-energy, high-resolution collimators commonly in use. With high-energy parallel-hole collimators, phantom studies show that the limit for detectability of "hot" lesions is 1.5 cm and 1.3 cm in diameter or larger for 2-[fluorine-18]fluoro-2-deoxy-D-glucose (FDG) uptake ratios of 5:1 and 10:1, respectively, if one assumes adequate counting statistics. Dual-isotope, single-acquisition techniques for using technetium-99m methoxy isobutyl isonitrile and FDG have been developed and proved useful in identification of ischemic but viable myocardium. High-energy fan-beam collimators have superior spatial resolution but inferior sensitivity relative to low-energy, high-resolution collimators. Metabolic images of the brain obtained with FDG demonstrate spatial resolution comparable with that of positron emission tomography, but such studies are often limited by inadequate counting statistics.
Asunto(s)
Cámaras gamma , Tomografía Computarizada de Emisión de Fotón Único/instrumentación , Tomografía Computarizada de Emisión/instrumentación , Encéfalo/diagnóstico por imagen , Desoxiglucosa/análogos & derivados , Radioisótopos de Flúor , Fluorodesoxiglucosa F18 , Corazón/diagnóstico por imagen , Humanos , Neoplasias/diagnóstico por imagen , Fantasmas de Imagen , Tecnecio Tc 99m Sestamibi , Tecnología Radiológica , Tomografía Computarizada de Emisión/métodos , Tomografía Computarizada de Emisión de Fotón Único/métodosRESUMEN
UNLABELLED: The purpose of this study was to develop a dual-isotope simultaneous acquisition (DISA) protocol using a multihead SPECT camera equipped with an ultrahigh-energy (UHE) collimator to evaluate simultaneously rest cardiac perfusion and metabolism with 99mTc-MIBI/18FDG. METHODS: Physical measurements were first performed with phantoms to develop the acquisition protocol. Fifteen patients underwent DISA-SPECT with 99mTc-MIBI/18FDG to validate the protocol. To evaluate the quality of the 99mTc-MIBI images acquired with the UHE collimator, four patients underwent a resting 99mTc-MIBI scan acquired with a high-resolution, low-energy collimator prior to DISA-SPECT. RESULTS: With a window of 20% for both photopeaks and a 99mTc/18F concentration ratio of 3.2:1, the spillover from 18F into the 99mTc window is 6% of the counts in the window for normal subjects. Phantom images clearly demonstrated defects measuring 2 x 1 and 2 x 0.5 cm. Technetium-99m-MIBI images obtained with the UHE and high-resolution collimators provided similar diagnostic information. Using a stenosis of > 70% as criteria to diagnose coronary artery disease, DISA-SPECT had a sensitivity of 100% and a positive predictive value of 93%. CONCLUSION: Simultaneous evaluation of rest myocardial perfusion/metabolism with a multihead SPECT camera equipped with an UHE collimator is possible using 99mTc-MIBI/18FDG with a dual-isotope simultaneous acquisition protocol.
Asunto(s)
Desoxiglucosa/análogos & derivados , Radioisótopos de Flúor , Corazón/diagnóstico por imagen , Isquemia Miocárdica/diagnóstico por imagen , Tecnecio Tc 99m Sestamibi , Tomografía Computarizada de Emisión de Fotón Único/métodos , Estudios de Factibilidad , Femenino , Fluorodesoxiglucosa F18 , Humanos , Procesamiento de Imagen Asistido por Computador , Masculino , Persona de Mediana Edad , Isquemia Miocárdica/metabolismo , Miocardio/metabolismo , Fantasmas de Imagen , Valor Predictivo de las Pruebas , Sensibilidad y Especificidad , Tomografía Computarizada de Emisión de Fotón Único/instrumentaciónRESUMEN
OBJECTIVES: This study sought to develop a dual-isotope single-acquisition single-photon emission computed tomographic (SPECT) protocol using a multihead SPECT camera equipped with an ultra-high energy collimator to evaluate rest metabolism/stress perfusion simultaneously with fluorine-18 (F-18) deoxyglucose/technetium-99m (Tc-99m) 2-hexakis-2-methoxy-2-methylpropyl isonitrile (MIBI). BACKGROUND: The most accurate and logistic method of identifying injured but viable myocardium remains a diagnostic challenge. METHODS: Sixty-five patients were given 25 to 50 g of glucose and, after approximately 60 min, an injection of 370 MBq (10 mCi) of F-18 fluorodeoxyglucose. After a 35-min distribution phase, patients underwent exercise or pharmacologic stress followed by administration of 925 MBq (25 mCi) of Tc-99m MIBI. Five patients underwent F-18 fluorodeoxyglucose position emission tomography before dual-isotope SPECT: RESULTS: With a window of 20% for both photopeaks and a technetium-99m/fluorine-18 concentration of 3.2:1, the "spillover" from fluorine-18 into the technetium-99m window is < 6% of the total counts in the window in patients with a normal distribution of both radiopharmaceuticals. Phantom images clearly demonstrated cardiac defects measuring 2 x 1 and 2 x 0.5 cm. There was no significant difference in the images of the five patients who underwent both positron emission tomography and SPECT: Fifty-seven patients (mean [+/- SD] age 55 +/- 15 years, range 25 to 83; 38 men, 19 women) had satisfactory images and were included in the study. Twenty-one patients had normal study results; 15 had mismatched defects; 14 had matched defects; and 7 had both matched and mismatched defects. Twenty-three patients (mean age 54 +/- 6 years, range 30 to 83; 14 men, 9 women) underwent coronary angiography within 3 months of dual-isotope SPECT: There were seven normal studies, eight with mismatched defects, one with a matched defect and seven with matched and mismatched defects. When stenosis > 70% was used as the criterion for a diagnosis of coronary artery disease, dual-isotope SPECT had a sensitivity of 100%, specificity of 88%, positive predictive value of 93%, negative predictive value of 100% and an accuracy of 96%. CONCLUSIONS: Dual-isotope SPECT may provide an alternative, accurate, cost-effective method to nitrogen-13 ammonia/F-18 fluorodeoxyglucose positron emission tomography or thallium-201 reinjection for identifying injured or dysfunctional but viable myocardium.
Asunto(s)
Desoxiglucosa/análogos & derivados , Radioisótopos de Flúor , Corazón/diagnóstico por imagen , Isquemia Miocárdica/diagnóstico por imagen , Tecnecio Tc 99m Sestamibi , Tomografía Computarizada de Emisión de Fotón Único/métodos , Angiografía Coronaria , Enfermedad Coronaria/diagnóstico por imagen , Enfermedad Coronaria/epidemiología , Dipiridamol , Prueba de Esfuerzo , Femenino , Fluorodesoxiglucosa F18 , Humanos , Masculino , Persona de Mediana Edad , Isquemia Miocárdica/epidemiología , Miocardio/metabolismo , Valor Predictivo de las Pruebas , Sensibilidad y Especificidad , VasodilatadoresRESUMEN
UNLABELLED: The clinical utility of FDG-PET imaging in the evaluation of patients with cardiac, oncologic and neurologic diseases is well documented. The major disadvantages of PET continue to be its high cost and limited availability. METHODS: With the goal of providing equivalent diagnostic information using a widely available, less expensive modality, we evaluated the clinical utility of FDG-SPECT imaging with a conventional dual-headed camera as compared to PET in 21 patients. RESULTS: To compare the image quality of the two modalities, major physical parameters and phantom determinations were obtained. By using the 511-keV collimators, we achieved resolution and system volume sensitivity that were less than those for PET by factors of 2.6 and 8, respectively. The SPECT system, on the other hand, could easily resolve 2 x 0.5-cm cold defects in the heart phantom and 2-cm hot lesions in a 22-cm cylindrical phantom with a target-to-background ratio of 5:1. FDG-SPECT imaging of nine patients with heart disease yielded similar diagnostic information of the amount of viable myocardium present when compared to PET. In seven of eight patients, malignant tissue visualized with FDG-PET was seen equally well with SPECT. The lesions not visualized with FDG-SPECT were either small (< or = 1.5 cm) or benign. SPECT imaging of four patients with cerebral lesions was inconclusive due to the small sample size but seemed promising. CONCLUSION: FDG-SPECT with 511-keV collimation is less expensive, more available and technically simpler than PET. We believe that FDG-SPECT has achieved sufficient sensitivity and resolution to detect myocardial viability and diagnose malignant tumors > or = 2 cm in diameter.