1.4.2.1. Positioner
A positioner (see Figure 1-3, B) mechanically attached to the cradle fixes the probe in place during the
treatment. However, it still allows automatic mechanical movement of the transducer inside the shell in
two dimensions. The positioner is designed so it would reduce pressure on the anus and eliminate any
motion in the anus during the treatment.
The positioner has six degrees of freedom to easily adjust it to the probe location after insertion.
1.4.2.2. Probe Shell
The probe shell (see Figure 1-4) function is to keep the rectum and the anus safe while allowing energy
delivery with minimum acoustic attenuation and dispersion and free mechanic transducer motion. The
shell’s dimensions and shape were designed to facilitate its insertion/extraction through the anus. The shell
has no sharp edges nor steps that could have harm the rectal wall, and its oblique tip is intended to facilitate
safe insertion. The transducer is locked in its position inside the shell while inserting or extracting it.
1.4.2.3. Transducer
The 990-elements phased array transducer was designed to be small yet powerful. It delivers ultrasound
energy in a frequency of 2.3 MHz for high energy absorption in the prostate tissue. It can deliver up to 60W
(acoustic); yet power is currently limited to 45W to avoid cavitation. The focus of the US beam transmitted
by the transducer at the working distance of 15mm to 60mm is ~1mm to ~2.5mm in diameter (according
to approximated measures of -6db contour), thus it creates well defined spot margins. This feature is
important for full tumor ablation, even when adjacent to vulnerable structures such as the nerve bundles
and the urethra.
The 990 elements of the phased array transducer enable electrical steering of the US beam 15mm-60mm
away from the transducer (A/P), +/-5 degrees transversally (R/L) and +/-10 degrees longitudinally (S/I); this
ability have a few implications, in addition to simple spot relocation. First, it increases the transducer
possible treatment range (mechanical 50mm in S/I and ±40 degrees roll) to allow total prostate coverage,
without passing the beam through the anus muscle. Second, it enables creating spots of various sizes and
shapes without moving the transducer, using a 'bean' shape building block. This allows good control of the
planned spots to maximize efficacy and safety.
1.4.2.4. MR Tracking Coils
The prostate motion system location control is based on relative encoders with index only. As an additional
safety measure, an MR tracking subsystem is used to verify the transducer spatial location before every
sonication and to re-aim it accordingly if necessary. The MR tracking subsystem includes four miniature
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