Bragi Sveinsson

Imaging and T2 relaxometry of short-T2 connective tissues in the knee using ultrashort echo-time double-echo steady-state (UTEDESS)

To develop a radial, double‐echo steady‐state (DESS) sequence with ultra‐short echo‐time (UTE) capabilities for T2 measurement of short‐T2 tissues along with simultaneous rapid, signal‐to‐noise ratio (SNR)‐efficient, and high‐isotropic‐resolution morphological knee imaging.

A simple analytic method for estimating T2 in the knee from DESS

PURPOSE To introduce a simple analytical formula for estimating T2 from a single Double-Echo in Steady-State (DESS) scan. METHODS Extended Phase Graph (EPG) modeling was used to develop a straightforward linear approximation of the relationship between the two DESS signals, enabling accurate T2 estimation from one DESS scan. Simulations were performed to demonstrate cancellation of different echo pathways to validate this simple model. The resulting analytic formula was compared to previous methods for T2 estimation using DESS and fast spin-echo scans in agar phantoms and knee cartilage in three volunteers and three patients. The DESS approach allows 3D (256×256×44) T2-mapping with fat suppression in scan times of 3-4min. RESULTS The simulations demonstrated that the model approximates the true signal very well. If the T1 is within 20% of the assumed T1, the T2 estimation error was shown to be less than 5% for typical scans. The inherent residual error in the model was demonstrated to be small both due to signal decay and opposing signal contributions. The estimated T2 from the linear relationship agrees well with reference scans, both for the phantoms and in vivo. The method resulted in less underestimation of T2 than previous single-scan approaches, with processing times 60 times faster than using a numerical fit. CONCLUSION A simplified relationship between the two DESS signals allows for rapid 3D T2 quantification with DESS that is accurate, yet also simple. The simplicity of the method allows for immediate T2 estimation in cartilage during the MRI examination.

Hexagonal undersampling for faster MRI near metallic implants

Slice encoding for metal artifact correction acquires a three‐dimensional image of each excited slice with view‐angle tilting to reduce slice and readout direction artifacts respectively, but requires additional imaging time. The purpose of this study was to provide a technique for faster imaging around metallic implants by undersampling k‐space.

SNR-weighted regularization of ADC estimates from double-echo in steady-state (DESS)

To improve the homogeneity and consistency of apparent diffusion coefficient (ADC) estimates in cartilage from the double‐echo in steady‐state (DESS) sequence by applying SNR‐weighted regularization during post‐processing.

Hexagonal Undersampling for Faster MR Imaging near Metallic Implants

Slice encoding for metal artifact correction acquires a three‐dimensional image of each excited slice with view‐angle tilting to reduce slice and readout direction artifacts respectively, but requires additional imaging time. The purpose of this study was to provide a technique for faster imaging around metallic implants by undersampling k‐space.

Hexagonal undersampling for faster MRI near metallic implants: Hexagonal Sampling for Faster MRI Near Metal Implants

Slice encoding for metal artifact correction acquires a three‐dimensional image of each excited slice with view‐angle tilting to reduce slice and readout direction artifacts respectively, but requires additional imaging time. The purpose of this study was to provide a technique for faster imaging around metallic implants by undersampling k‐space.