Avances en Tomografia Computada

Dosis en TC Doble Energia.GSIGeneral Electric TM MsC. PhD Cristian Cabrera G.

Conflictos de InteresConsultor externo General Electric. Division medios de contraste.

Consultor Externo Medrad Inc.

Objetivos

TC Energia DualLas bases fisicas de esta tecnica se basan en la dependencia de la energia con el Efecto Fotoelectrico y la capa K caracteristica de cada elemento.

The K-shell binding energy varies for each element, and it increases as the atomic number increases. The term K edge refers to the spike in attenuation that occurs at energy levels just greater than that of the K-shell binding because of the increased photoelectric absorption at these energy levels. K-edge values vary for each element, and they increase as the atomic number increases Attenuation spectrum of different materials at differ-ent X-ray energies. At a low kilovoltage, materials with a highmolecular weight (mainly iodine) show greater X-ray absorption dueto a greater likelihood of the photoelectric effect occurring.4

Area Clave de Desarrollo

Emision Haz Policromatico

A, Spectra of x-ray tube at 70, 80, 100, 120, and 140 kV with 0.9-mm titanium and 3.5-mm aluminum filter and at 140 kV with additional 0.4- or 1-mm tin filter. Peaks represent characteristic lines of tungsten anode, and continuous spectrum is result of bremsstrahlung. At equal currents, tube efficiency is optimal at 140 kVp, whereas photon output is significantly reduced in filtered spectra and at 70 kVp.6

Principios de Descomposicion de Materiales BasesAlvarez RE, Macovski A. Phys Med Biol 1976; 21; 733-744

Principio Descomposicion 3 Materiales

Basado en diferencias de atenuacion en diferentes niveles de energia

Principle of the three-material decomposition of a voxel used by the dualenergy software. This software splits every voxel in the 80- and 140-kV image pair into three components represented by brain parenchyma ( BP ), hemorrhage ( ICH ), and iodine, which are empirically estimated: The intercepts x and y correspond to the portion of brain parenchyma and ICH in the voxel, whereas the intercept z along the iodine axis represents the iodine content of the voxel on this two-energy plot. To the extent the measured value of a voxel does not conform to a mixture of brain parenchyma and ICH, the difference can be attributed toiodine. The virtual unenhanced images display the noniodine component of the voxel (ie, the brain parenchyma and ICH represented by x and y), and the overlay images display the z intercept (ie, the iodine content).8

Descomposicion de Material

Imgenes MonocromaticasRepresentacion de objeto de imagen si la fuente de rayos x produce solo fotones de rayos X en una sola energia.

If projection-based beam hardening correction through two different materials can be performed by using two different kVp data for the same projection angle, the rigorous beam hardening correction will be available, which enables to reconstruct virtual monochromatic (VMS) image.

10

Ventajas y Desventajas

Discovery CT750HDRapido intercambio kVp (250 ms).Nueva gama de cristales de centelleo , con velocidad de respuesta ultrarapida.Adquisicion de datos en 80 y 140 kVp, son analizados como proyecciones coincidentes temporal y espacialmente.

TC Intercambiador Kvp

GSI

Ultrarapido intercambio Kvp/Detectores respuesta Ultrarapida

Ultrarapido intercambio Kvp/Detectores respuesta Ultrarapida

Sistema Dual Energy General Electric

Evaluacion Especial

Espectro MonoenergeticoLa imagen en TC no calcula correctamente el coeficiente de atenuacion de los materiales para cada haz de rayos x.Emision de rayos X con distinto potencial para generar imgenes monocromaticas.

70 Kev.MD IodoMD Agua

Procesamiento Datos

Algorithm is used for decomposition of three materials. Two basic components define one slope, and inclination of second slope is defined by photoelectric effect of iodine. Iodine content can be quantified and color-coded by displacement of measured pair of density values along second slope (Figs. 4G and 4I). Virtual unenhanced density is represented by intersection of both slopes21

Aplicaciones

Aprobadas por FDA

Efectos Imagen Monocromatica

Reduccion Artefacto Metalico

140 KvpPolicromatico75 kevMonocromatico

the fact that each pair of projections (each dataset pair) is obtained at the same point along the pathway through the patient, which results in the immediate cancellation of most beam hardening errors. 26

Evaluacion Fase Virtualsin Medio de Contraste

Pre Contraste Virtual

70 Kev MonocromaticoMD Agua140 Kvp PolicromaticoNo contrastado

Evaluacion Ostearticular

Gota/ Pseudogota

MD Acido UricoMD Calcio70 kev Acido UricoDiferenciacion Acido Urico / Fosfato de Calcio. MD Acido Urico sugiere depositos de Acido Urico en tejidos blandos.

Composicion-Diferenciacion de tejidos

Graph shows how compo-sition of tissues is determined. Mate-rial-specific differences in attenuation (measured in HU and not to scale) between the 80- and 140-kV acquisitions help determine chemical composition of scanned tissues.31

Caracterizacion Calculos Renales

Aplicaciones Clinicas.Sin realce Virtual

Es Reproducible a la imagen real?

33La reconstruccin VNC nos permite detectar clculos en estudios en fase excretora con la va opacificada.

Son comparativos los valores obtenidos en forma real y virtual?Sin Realce RealSin Realce Virtual30.8 +- 4 UH31,6 +- 7,1 UH

No hay variacion estadisticamente significativaGraser et al.

Y la Dosimetria asociada?

Avances Disminucion Dosis Filtracion Proyeccion Dinamica.Filtros Suavizacion eje Z.Smart Prep.Colimador Variable.Automa.Smartma.NeuroFiltro.Modulacion ma-ECGCodigo de Color Exs. Pediatricos.Diodos Retroiluminados.Snapshot Pulse.ASIR (2008).Helical Shuttle.Helical Shutter.MBIR (VEO) (2010).TC con Conteo de Fotones.

TC Corte Unico1990TC Multicanal2000TC Volumetrico2010

Modelo Reconstruccion Iterativa

Evolucion Reconstruccion Imagen TC

RetroproyeccionFiltrada

RetroproyeccionFiltrada DirectaRetroproyeccionFiltrada Directa con correccion Iterativa de imagenRaw DataASIRReconstruccion Iterativa. Modelo avanzado sistema Estadistico

VEOReconstruccion Iterativa Comprehensiva.Modelo Estadistico Avanzado.Modelo Optico Avanzado.

Reduccion de Dosis ASIR

FBPASIRCTDI 19CTDI 5,8

Abd-Pelvis de rutina con VEO

FBPVEO0.68 msV450 mm.

Dosis en Dual Energy?Hay bastante evidencia de que esta tecnica con sistema de Doble Fuente, no esta asociada con aumento en los niveles de dosis de radiacion.

En relacion a la tecnica basada en Intercambio de Kvp, no hay datos concluyentes aun. Dual-Energy CT:Radiation Dose Aspects.Henzler.Fink.Schoepf.AJR nov 2012

Dosis en Intercambiador de Kvp??Mayor aporte de dosis cuando?Al comparar Dual energy con con una sola energia exploratoria.5 a 30% mayor. 340 mgy-cm en relacion a 475 mgy-cm.(torax)Incorporacion IR , disminucion 20 a 50%Geyer LL, Scherr M, Korner M, Wirth S, Deak P, Reiser MF,et al. Imaging of acute pulmonary embolism using a dual energy CT system with rapid KVp switching: initials results: Eur J Radiol 2012; 81(12): 3711-8.

En que estamos hoy?TC con intercambiador rapido de KV, tambien muestra niveles de dosis de radiacion similares a TC convencionales.Como disminuimos aun mas la dosis de radiacion con este equipamiento?

Zhang D, Li X, Liu B. Objetive characterization of GE discovery CT750HD scanner: gemstone spectral imagin mode. Med Phys 2013: 38(3):1178-1188

those performed with conventional abdominal CT with a similar volume CT dose index, found that diagnostic performance based on the interpretation of 65-keV monochromatic dual-energy CT images was equivalent to that based on the interpretation of conventional CT images 43

En que estamos hoy?GSIImagen sin contraste virtualASIR VEO

CaracteristicasMayor Transparencia y Uniformidad.100 veces mas veloz la respuesta de reaccion a los rayos x que los elementos actuales( 3 microseg de GSO, 0,03 microseg de GEM).4 veces mayor % de afterglow y resplandor de GEM (0,001%) versus 0.004% GSO.Aumento Alta Resolucion hasta 230 micrones.Resolucion de 18,2 lp/cm.

Beneficios??

77-year-old man with aortic dissection. Calculated monoenergetic dual-energy CT images of aorta from 120 keV (left upper image) to 40 keV (right lower image)show increasing vessel attenuation at lower keV levels. Best contrast-to-noise ratio was achieved at 70 keV (second image of lower row). Radiation dose parameters:dose-length product, 546 mGy ~ cm; volume CT dose index, 7.96 mGy.47

Conclusion

Muchas Gracias por su Atencion