Jose Azevedo

Two‐Dimensional Real‐time Ultrasound Technique to Control Lesion Size during HIFU Therapy

The lack of accurate and low‐cost techniques for real‐time monitoring and feedback during ablative therapies such as HIFU has limited its widespread clinical adoption. A good ultrasound solution would enable a much more widespread usage of HIFU therapy. An acoustic radiation force (ARF) based technique for controlling the lesion size and its placement during HIFU therapy has been developed. A series of experiments were performed in excised bovine liver tissue to evaluate the proposed technique. The change in the ARF induced displacements during therapy at each spatial location was quantified by a unitless parameter, normalized displacement difference (NDD), defined as the difference between normalized displacement at the therapy endpoint and a reference determined from the data. The 2‐D displacement map (normalized to the value before therapy commenced) illustrated that displacements initially increased due to the temperature rise, reached a maximum, and then decreased with continuing therapy. Strong corr...

Monitoring of radiofrequency ablation with shear wave delay mapping

Real-time monitoring of radiofrequency ablation is important to ensure adequate treatment coverage of liver tumors as well as protection of healthy tissues. The high stiffness contrast between ablated and non-treated tissues has led to the use of ultrasound elastography for coagulation zone visualization. A highly sensitive shear wave delay mapping approach was developed for ablation boundary detection, especially, in the presence of a rigid ablation needle. The shear wave technique was evaluated using ex-vivo bovine and porcine liver samples as well as whole livers from sedated live and fresh cadaver pigs. Initial tissue softening was seen ex-vivo for non-perfused livers, but not observed in-vivo for live livers with `cooling blood perfusion. The lesion sizes (lateral radii) determined by the shear wave technique were generally in good agreement with those from gross pathology. In addition, T2-weighted MR images were acquired in 3D for direct assessments of ablated tissue volumes. Overall the shear wave technique appears feasible for defining and monitoring the progression of thermal lesion boundary.

Validating Ultrasound‐based HIFU Lesion‐size Monitoring Technique with MR Thermometry and Histology

In order to control and monitor HIFU lesions accurately and cost‐effectively in real‐time, we have developed an ultrasound‐based therapy monitoring technique using acoustic radiation force to track the change in tissue mechanical properties. We validate our method with concurrent MR thermometry and histology. Comparison studies have been completed on in‐vitro bovine liver samples. A single‐element 1.1 MHz focused transducer was used to deliver HIFU and produce acoustic radiation force (ARF). A 5 MHz single‐element transducer was placed co‐axially with the HIFU transducer to acquire the RF data, and track the tissue displacement induced by ARF. During therapy, the monitoring procedure was interleaved with HIFU. MR thermometry (Philips Panorama 1T system) and ultrasound monitoring were performed simultaneously. The tissue temperature and thermal dose (CEM43u2009=u2009240u2009mins) were computed from the MR thermometry data. The tissue displacement induced by the acoustic radiation force was calculated from the ultrasou...

Two‐dimensional real‐time ultrasound technique to control lesion size during high intesity focused ultrasound therapy.

The lack of an accurate low‐cost technique for real‐time monitoring of ablative therapies such as HIFU has limited its clinical adoption. Ultrasound based monitoring would enable a more widespread usage of HIFU therapy. We have developed an acoustic radiation force (ARF) based technique for controlling the lesion size and placement during HIFU therapy. A series of experiments were performed in excised bovine liver tissue to evaluate the proposed technique. Two different parameters were developed to perform real‐time monitoring of lesions. The first parameter, normalized displacement difference (NDD), is defined as the difference between normalized displacement induced by ARF at the therapy endpoint and a reference determined from the data. This parameter was accurate in determining lesion sizes below 8 mm in diameter as independently determined by histological examination. The lesion dimensions estimated with this noninvasive approach matched histology to within ±2 mm. A second approach was based on the s...