Showing papers by "Scott D. Swanson published in 2005"

Hepatic fat fraction: MR imaging for quantitative measurement and display--early experience.

Abstract: The institutional review board approved this HIPAA-compliant study. After all five patients with nonalcoholic fatty liver disease signed a consent, they underwent magnetic resonance (MR) imaging for hepatic fat quantification. The purpose of this study was to develop a fast and accurate method to acquire and display quantitative maps of the percentage of hepatic fat. In-phase and out-of-phase gradient-echo MR imaging was performed with dual flip angles (70°, 20°) to resolve ambiguity of the dominant constituent. T2* corrections were also estimated and applied to generate color-coded maps of the estimated percentage of hepatic fat. MR imaging results were compared with biopsy results in two of five patients, and the technique was validated qualitatively and quantitatively with a water-oil phantom. Results of the phantom study confirmed that the dual–flip angle algorithm can be used to correctly identify the dominant constituent, allowing depiction of 0%–100% of fat content. The estimated liver fat fraction...

Magnetic resonance elastography using time reversed acoustics

Abstract: Recent efforts in medical imaging have shown that mechanical stimulation of tissues and a suitable imaging modality can be used to interrogate elastic properties of human tissues. Malignant tissues can have elastic properties that allow the physician to separate them from benign counterparts or plaque in arteries can be characterized in regard to its age by measuring its elastic properties. Our system consists of: (1) an acoustic source to induce tissue displacement, (2) a tissue mimicking phantom, and (3) MRI as a method for imaging and measuring the induced shear wave in the phantom. Agar was used to construct a tissue mimicking phantom. A modified spin echo sequence was written to trigger the acoustic system and phase encode the displacement information with magnetic field gradients. A series of images was obtained from the modified multi-slice, spin-echo sequence. Images showed z-axis displacement created by the radiation force. Additional experiments recorded the x and y displacement and allowed for a full 3D vector reconstruction of shear wave propagation. MRI provides a method to record displacements created by radiation force. Acoustical sources can be used to induce shear waves, which in turn can be imaged with MRI methods to quantify and display this wave in a 3D fashion.

Acoustically induced tissue displacement for shear wave elasticity imaging using MRI

Abstract: Palpitation detects tissue abnormalities by exploiting the vast range of elastic properties found in vivo. The method is limited by tactile sensitivity and the inability to probe tissues at depth. Recent efforts seek to remove these limitation by developing a medical imaging modality based on radiation force shear wave excitation. Our approach uses an acoustic source to launch a shear wave in a tissue‐mimicking phantom and MRI to record microscopic displacements. Gelatin (10% wt/vol) was used for the tissue‐mimicking phantom. Results for in situ elasticity were obtained using an air‐backed 10‐cm‐diam piezoelectric crystal. To correct for future in vivo beam aberrations, we also employ a high‐pressure 1‐bit time‐reversal cavity. Frequency and pulse duration were selected to optimize the TRA system for acoustic output pressure. Shear wave displacements were recorded by MRI in 1‐ms time increments in a complete basis that allowed for 3‐D reconstruction and analysis. The Lame coefficients are then derived fro...