Energy-based scatter estimation in clinical PET.

BACKGROUND: Scatter correction (SC) is essential in PET for accurate quantitative imaging. The state-of-the-art SC method is single-scatter simulation (SSS). Although this method is usually robust and accurate, it can fail in some situations, for example when there is motion between the CT and PET scans in PET/CT. Therefore, it is of interest to consider other SC methods. PURPOSE: In this work, an energy-based scatter estimation (EBS) method is described in detail, tested in phantoms and patients, and compared to SSS. METHODS: This version of EBS was developed for list-mode data from Biograph Vision-600 PET/CT scanner. EBS is based on digitized 2D energy histograms in each bin of a coarsely sampled PET sinogram, either with or without time of flight (TOF). The histograms are modeled as a noisy realization of a linear combination of nine basis functions whose parameters were derived from a measurement of the 511-keV photopeak spectrum as well as Monte-Carlo simulations of the scattering process. EBS uses an iterative expectation maximization approach to determine the coefficients in the linear combination, and from this estimates the scatter. The investigation was restricted to 18 F-based PET data in which the acquired number of counts was similar to the levels seen in oncological whole-body PET/CT scans. To evaluate the performance, phantom scans were used that involved the NEMA NU2-2018 protocol, a slab phantom, an NU 2-1994 phantom, a cardiac phantom in an anthropomorphic chest phantom, and a uniformly-filled torso phantom with a bladder phantom slightly outside the axial field of view. Contrast recovery (CR) and other parameters were evaluated in images reconstructed with SSS and EBS. Furthermore, FDG PET scans of seven lung cancer patients were used in the evaluation. Standardized uptake values (SUV) based on SSS and EBS were compared in 27 lesions. RESULTS: EBS and SSS images were visually similar in all cases except the torso + bladder phantom, where the EBS was much closer to the expected uniform image. The NU2-2018 analysis indicated a 2% scatter residual in EBS images compared to 3% with SSS, and 10% higher background variability, which is a surrogate for image noise. The cardiac phantom scan showed that CR was 98.2% with EBS and 99.6% with SSS, and that the SSS sinogram had values greater than the net-true emission sinogram, indicating a slight overcorrection in the case of SSS. In the lesion SUV comparison in patient scans, EBS correlated strongly (R2  = 0.9973) with SSS, and SUV based on EBS were systematically 0.1 SUV lower. In the case of the torso + bladder phantom portion, the SSS image of the torso + bladder phantom was 299% times hotter than expected in one area, due to scatter estimation error, compared to 16% colder with EBS. CONCLUSIONS: In evaluating clinically relevant parameters such as SUV in focal lesions, EBS and SSS give almost the same results. In phantoms, some scatter figures of merit were slightly improved by use of EBS, though an image variability figure of merit was slightly degraded. In typical oncological whole-body PET/CT, EBS may be a suitable replacement for SSS, especially when SSS fails due to technical problems during the scan.

Almost 10 years of PET/MR attenuation correction: the effect on lesion quantification with PSMA: clinical evaluation on 200 prostate cancer patients.

PURPOSE: After a decade of PET/MR, the case of attenuation correction (AC) remains open. The initial four-compartment (air, water, fat, soft tissue) Dixon-based AC scheme has since been expanded with several features, the latest being MR field-of-view extension and a bone atlas. As this potentially changes quantification, we evaluated the impact of these features in PET AC in prostate cancer patients. METHODS: Two hundred prostate cancer patients were examined with either 18F- or 68Ga-prostate-specific membrane antigen (PSMA) PET/MR. Qualitative and quantitative analysis (SUVmean, SUVmax, correlation, and statistical significance) was performed on images reconstructed using different AC schemes: Dixon, Dixon+MLAA, Dixon+HUGE, and Dixon+HUGE+bones for 18F-PSMA data; Dixon and Dixon+bones for 68Ga-PSMA data. Uptakes were compared using linear regression against standard Dixon. RESULTS: High correlation and no visually perceivable differences between all evaluated methods (r > 0.996) were found. The mean relative difference in lesion uptake of 18F-PSMA and 68Ga-PSMA remained, respectively, within 4% and 3% in soft tissue, and within 10% and 9% in bones for all evaluated methods. Bone registration errors were detected, causing mean uptake change of 5% in affected lesions. CONCLUSIONS: Based on these results and the encountered bone atlas registration inaccuracy, we deduce that including bones and extending the MR field-of-view did not introduce clinically significant differences in PSMA diagnostic accuracy and tracer uptake quantification in prostate cancer pelvic lesions, facilitating the analysis of serial studies respectively. However, in the absence of ground truth data, we advise against atlas-based methods when comparing serial scans for bone lesions.

Simultaneous characterization of tumor cellularity and the Warburg effect with PET, MRI and hyperpolarized 13C-MRSI.

Modern oncology aims at patient-specific therapy approaches, which triggered the development of biomedical imaging techniques to synergistically address tumor biology at the cellular and molecular level. PET/MR is a new hybrid modality that allows acquisition of high-resolution anatomic images and quantification of functional and metabolic information at the same time. Key steps of the Warburg effect-one of the hallmarks of tumors-can be measured non-invasively with this emerging technique. The aim of this study was to quantify and compare simultaneously imaged augmented glucose uptake and LDH activity in a subcutaneous breast cancer model in rats (MAT-B-III) and to study the effect of varying tumor cellularity on image-derived metabolic information. Methods: For this purpose, we established and validated a multimodal imaging workflow for a clinical PET/MR system including proton magnetic resonance (MR) imaging to acquire accurate morphologic information and diffusion-weighted imaging (DWI) to address tumor cellularity. Metabolic data were measured with dynamic [18F]FDG-PET and hyperpolarized (HP) 13C-pyruvate MR spectroscopic imaging (MRSI). We applied our workflow in a longitudinal study and analyzed the effect of growth dependent variations of cellular density on glycolytic parameters. Results: Tumors of similar cellularity with similar apparent diffusion coefficients (ADC) showed a significant positive correlation of FDG uptake and pyruvate-to-lactate exchange. Longitudinal DWI data indicated a decreasing tumor cellularity with tumor growth, while ADCs exhibited a significant inverse correlation with PET standard uptake values (SUV). Similar but not significant trends were observed with HP-13C-MRSI, but we found that partial volume effects and point spread function artifacts are major confounders for the quantification of 13C-data when the spatial resolution is limited and major blood vessels are close to the tumor. Nevertheless, analysis of longitudinal data with varying tumor cellularity further detected a positive correlation between quantitative PET and 13C-data. Conclusions: Our workflow allows the quantification of simultaneously acquired PET, MRSI and DWI data in rodents on a clinical PET/MR scanner. The correlations and findings suggest that a major portion of consumed glucose is metabolized by aerobic glycolysis in the investigated tumor model. Furthermore, we conclude that variations in cell density affect PET and 13C-data in a similar manner and correlations of longitudinal metabolic data appear to reflect both biochemical processes and tumor cellularity.

Síndrome de Ehlers Danlos, ¿subregistro clínico en ortopedia pediátrica? / Ehlers Danlos syndrome, a clinical subregister in pediatric orthopedics?

Introducción. El comportamiento del síndrome de Ehlers Danlos hizo que se interpretara como un subregistro clínico, poco conocido y con escasas referencias. Esta genodermatosis generalmente está condenada a no tener un tratamiento específico. El objetivo del presente estudio fue, principalmente, describir la morbilidad de este síndrome, desde el punto de vista ortopédico. Métodos. Se realizó un estudio descriptivo prospectivo de 5 años, que incluyó a todos los pacientes con síndrome de Ehlers Danlos, atendidos en la consulta de ortopedia y traumatología entre julio de 2001 y julio del 2006, en el Hospital Pediátrico Docente José Martí (Sancti Spiritus, Cuba). Se consideró un tiempo mínimo de seguimiento de 6 meses para la validación de los resultados. Resultados. Fueron estudiados 41 pacientes afectos de 72 enfermedades de origen ortopédico. La frecuencia estuvo próxima a 1,7 enfermedades por paciente, con predominio no significativo del sexo femenino (n = 24). Uno de los antecedentes perinatales más importantes fue la presencia de grados diversos de displasia de la cadera. La presencia de otras afecciones no ortopédicas no fue significativa. Los principales hallazgos ortopédicos fueron el pie plano flexible (37), el genus recurvatum (11) y la cifoescoliosis (9). La cirugía estética y la cirugía correctora ortopédica fueron las más utilizadas. Conclusiones. La dispensarización de esta enfermedad y su tratamiento oportuno es un método de control eficaz que ayudaría a evitar la degeneración articular, generalmente antesala de la osteoartrosis.

Introduction. The behavior of Ehlers Danlos syndrome caused it to be interpreted as a clinical subregister, little known, and with a few references. This genodermatosis is generally condemned not to have a specific treatment. The objective of this study was mainly to describe the morbidity of this syndrome from the orthopedic point of view. Methods. A 5-year prospective and descriptive study was conducted among all the patients with Ehlers Danlos syndrome that were seen at the Orthopedics and Traumatology department of José Martí Teaching Pediatric Hospital (Sancti Spiritus, Cuba) from July 2001 to July 2006. A minimum follow-up time of 6 months was considered for the validation of the results. Results. 41 patients affected with 72 diseases of orthopedic origin were studied. The frequency was approximately 1.7 diseases per patient, with a non significant predominance of females (n = 24). One of the most important perinatal antecedents was the presence of diverse hip dysplasia degrees. The presence of other non-orthopedic affections was not remarkable. The main orthopedic findings were the flexible flat foot (37), the genus recurvatum (11) and kyphoscoliosis (9). Aesthetic surgery and the corrective orthopedic surgery were the most used. Conclusions. The categorization of this disease and its timely treatment is an efficient method of control that would help to prevent the articular degeneration that generally precedes osteoarthritis.

Validación clínica del inmunoensayo rápido BioLine-hCG para el diagnóstico precoz del embarazo / Clinical validation of BioLine-hCG rapid immunoassay for the early diagnosis of pregnancy

Se realizó la validación clínica del inmunoensayo rápido y simple BioLine-hCG para el diagnóstico precoz del embarazo, en el Hospital Ginecoobstétrico de la Provincia de Sancti Spíritus. Se analizaron 397 muestras de orina, 150 de las cuales correspondían a pacientes que asistían a la Consulta de Regulación Menstrual. Se compararon los resultados obtenidos con el diagnóstico cromatográfico de referencia ABBOTT TestPack+Plus, el examen físico inferido por el ginecólogo y el análisis histopatológico efectuado por el laboratorio de patología del propio hospital. Se comprobó en el sistema BioLINE-hCG, el 99,07 porciento de sensibilidad y 100 porciento de especificidad para el 99,33 porciento de exactitud con respecto al diagnóstico de referencia. De poseer un diagnóstico rápido y sencillo como el validado en este trabajo, la interesada puede conocer el resultado y evitar todos los riesgos que acarrean los procesos de interrupción del embarazo en la mujer