RESUMEN
Current 4D-CT methods require external marker data to retrospectively sort image data and generate CT volumes. In this work we develop an automated 4D-CT sorting algorithm that performs without the aid of data collected from an external respiratory surrogate. The sorting algorithm requires an overlapping cine scan protocol. The overlapping protocol provides a spatial link between couch positions. Beginning with a starting scan position, images from the adjacent scan position (which spatial match the starting scan position) are selected by maximizing the normalized cross correlation (NCC) of the images at the overlapping slice position. The process was continued by 'daisy chaining' all couch positions using the selected images until an entire 3D volume was produced. The algorithm produced 16 phase volumes to complete a 4D-CT dataset. Additional 4D-CT datasets were also produced using external marker amplitude and phase angle sorting methods. The image quality of the volumes produced by the different methods was quantified by calculating the mean difference of the sorted overlapping slices from adjacent couch positions. The NCC sorted images showed a significant decrease in the mean difference (p < 0.01) for the five patients.
Asunto(s)
Algoritmos , Procesamiento de Imagen Asistido por Computador/métodos , Artefactos , Automatización , Humanos , Procesamiento de Imagen Asistido por Computador/normas , Neoplasias/diagnóstico por imagen , Neoplasias/patología , Neoplasias/fisiopatología , Radiografía Torácica , Estándares de Referencia , Respiración , Tomografía Computarizada por Rayos XRESUMEN
UNLABELLED: Heart disease is a leading cause of death in North America. With the increased availability of PET/CT scanners, CT is now commonly used as a transmission source for attenuation correction. Because of the differences in scan duration between PET and CT, respiration-induced motion can create inconsistencies between the PET and CT data and lead to incorrect attenuation correction and, thus, artifacts in the final reconstructed PET images. This study compared respiration-averaged CT and 4-dimensional (4D) CT for attenuation correction of cardiac PET in an in vivo canine model as a means of removing these inconsistencies. METHODS: Five dogs underwent respiration-gated cardiac (18)F-FDG PET and 4D CT. The PET data were reconstructed with 3 methods of attenuation correction that differed only in the CT data used: The first method was single-phase CT at either end-expiration, end-inspiration, or the middle of a breathing cycle; the second was respiration-averaged CT, which is CT temporally averaged over the entire respiratory cycle; and the third was phase-matched CT, in which each PET phase is corrected with the matched phase from 4D CT. After reconstruction, the gated PET images were summed to produce an ungated image. Polar plots of the PET heart images were generated, and percentage differences were calculated with respect to the phase-matched correction for each dog. The difference maps were then averaged over the 5 dogs. RESULTS: For single-phase CT correction at end-expiration, end-inspiration, and mid cycle, the maximum percentage differences were 11% +/- 4%, 7% +/- 3%, and 5% +/- 2%, respectively. Conversely, the maximum difference for attenuation correction with respiration-averaged CT data was only 1.6% +/- 0.7%. CONCLUSION: Respiration-averaged CT correction produced a maximum percentage difference 7 times smaller than that obtained with end-expiration single-phase correction. This finding indicates that using respiration-averaged CT may accurately correct for attenuation on respiration-ungated cardiac PET.
Asunto(s)
Artefactos , Corazón/diagnóstico por imagen , Aumento de la Imagen/métodos , Interpretación de Imagen Asistida por Computador/métodos , Tomografía de Emisión de Positrones/métodos , Mecánica Respiratoria , Tomografía Computarizada por Rayos X/métodos , Animales , Perros , Fantasmas de Imagen , Reproducibilidad de los Resultados , Sensibilidad y EspecificidadRESUMEN
Automated seed loaders for permanent prostate implants are now commercially available. Besides improved radiation safety, these systems offer seed assay capability and ease of needle loading, making preplanned as well as intra-operative implant procedures more time-efficient. The Isoloader (Mentor Corp., CA) uses individual I125 seeds (SL-125 ProstaSeed) loaded in up to 199 chambers inside a shielded cartridge. The unit performs seed counting and calibration using a builtin solid-state detector. In order to evaluate the reproducibility and accuracy of the calibration process, two test cartridges were measured with the Isoloader itself and compared with a well-type ionization chamber (HDR-1000Plus, Standard Imaging). The air kerma strength measurements for all seeds using the Isoloader had a standard deviation of about 2.7%. For the eight seeds assayed more intensively using both the Isoloader and well chamber, the standard deviations of the measurements for each seed were in the range of 0.8% to 2.8% and 0.6% to 1.3%, respectively. The variation in the Isoloader calibration is attributed to small detector solid angle and bead geometry within seed capsules (verified by radiographs). The reproducibility of the air kerma strength measured by the Isoloader was comparable to that from the well chamber and was clinically acceptable. Seed strength measured with the Isoloader was on average 1% 2% larger than that measured with the well chamber, indicating that the accuracy of the Isoloader was clinically acceptable.