Funded by the Research promotion foundation (2001-2003).
The objective of this program was the development of a High Intensity Focused Ultrasound (HIFU) system integrated with MRI. In this program the existing HIFU system was integrated with MRI in order to monitor the thermal effects of ultrasound.
The transducer and the positioning device have been designed so as to include minimum amount of magnetic materials. This is important because magnetic materials affect the quality of the MRI images. The positioning device (slave) is controlled by a master system, which sits outside the MRI room.
The effectiveness of MRI to monitor therapeutic protocols of HIFU in freshly excised pig Kidney cortex and liver was investigated. For high quality imaging the pulse sequence FSE (T1, and T2-weighted, and Proton Density) were evaluated. For fast imaging the pulse sequence T1-weighted FSPGR was used. The main goal was to evaluate the MR detection of large lesions. The contrast between lesion and kidney tissue is excellent with either T1-weighted or T2-weighted FSE. With T1-weighted FSE best contrast is observed for TR between 200 ms and 400 ms. With T2-weighted FSE best contrast can be achieved for TE between 16 and 32 ms.
T2-weighted FSE was proven as the best pulse sequence to detect cavitational activity. This advantage is attributed to the significant difference in signal intensity between air spaces and necrotic tissue. Air spaces appear brighter than thermal lesions.
The above techniques were very successful in detecting large lesion
volumes. In order to monitor small single lesions (smaller than 2
mm in diameter) the value of NEX must be increased. It was found
that using T2-weighted FSE the value of NEX must be greater than 3, which
makes this pulse sequence impractical because of the long acquisition time.
The same protocols that have been evaluated in tissues in vitro, have been tested in vivo having the same success. The next step is to do more in vivo experiments and when we prove that the system is reliable we will perform clinical studies. Because of the low cost of the system and its many advantages we expect that it will be a success commercially, provided that we will overcome all the obstacles that may be encountered due to the fact that Cyprus is a country having only few years of research culture.
Diagram of the MR/HIFU system
MRI images of HIFU lesions
Photos of large lesions