RESUMEN
It is shown that a spin-echo sequence may be used to acquire T(2)-weighted, high-resolution, high-SNR sections at quasi-real-time frame rates for interactive, diagnostic imaging. A single-shot fast spin-echo sequence was designed which employs driven equilibrium to realign transverse magnetization remaining at the final spin echo. Driven equilibrium is shown to improve T(2) contrast at a given TR, or conversely to reduce TR by approximately 1000 msec and thus increase temporal resolution while maintaining a given level of contrast. Wiener demodulation of k-space data prior to reconstruction is shown to reduce blurring caused by T(2)-decay while constraining noise often associated with other inverse filters. Images are continuously acquired, reconstructed, and displayed at rates of one image every one to two seconds, while section position and contrast may be altered interactively. The clinical utility of this method is demonstrated with applications to dynamic pelvic floor imaging and interactive obstetric imaging.
Asunto(s)
Neoplasias Faciales/diagnóstico , Enfermedades Fetales/diagnóstico , Aumento de la Imagen/métodos , Imagen por Resonancia Magnética/métodos , Complicaciones Neoplásicas del Embarazo/diagnóstico , Procesamiento de Señales Asistido por Computador , Sistemas de Computación , Neoplasias Faciales/embriología , Femenino , Geles/análisis , Humanos , Imagen por Resonancia Cinemagnética/métodos , Modelos Teóricos , Diafragma Pélvico/patología , Fantasmas de Imagen , Aceites de Plantas/análisis , Embarazo , Diagnóstico Prenatal , Rectocele/diagnóstico , Agua/análisisRESUMEN
The properties of tomography, K-edge imaging, and K-edge tomography are discussed in relation to the imaging of small concentrations of elements such as iodine and xenon and are compared by means of phantom images. It is demonstrated that the complementary selectivities provided by depth and energy subtraction are combined in K-edge tomography. Using a three-spectrum subtraction technique, the iodine difference signal predicted by computer calculations is on the order of 8000 times that of an equal concentration fo bone. The corresponding ratio in tomography without energy subtraction is 20:1. It is argued that K-edge tomography can successfully eliminate artifacts due to tissue inhomogeneities which presently enable 0.6% variations in tissue attenuation to mimic minimum detectable iodine signals in conventional computed tomography. Various instrumentation possibilities and energy subtraction techniques are discussed.