Biomedical Engineering Reference
In-Depth Information
(a)
(b)
Probe
Motion
unit
Positioner
(c)
(d)
FIGURE 11.3
ExAblate Prostate System by InSightec for MR guided ablation of prostate cancer: (a) endorectal phased array applicator integrated
with GE MRI system; (b) sagittal image of endorectal applicator positioned in rectum adjacent to prostate and treated region highlighted in the
circle; (c, d) accurate spatial and temporal temperature distributions and thermal dose mapped in real time and correlated to treatment plan and
target region. (Courtesy of Christopher Wai Sam Cheng, MD, Urology Department, Singapore General Hospital, Singapore, and Jin Wei Kwek,
MD, Radiology Department, National Cancer Center, Singapore.)
of real-time temperature monitoring and feedback control, and
running time thermal dose calculation can be used to verify lethal
thermal exposures within treatment regions. Additional treat-
ment verification immediately post-procedure can be obtained by
T1-contrast enhanced image studies to identify perfusion deficits
associated with treated areas. Based upon a patient specific treat-
ment plan, regions in each axial slice of the prostate as indicated
region of target are sonicated and monitored using temperature
and thermal dose as feedback, sweeping out and conforming to
target region (Figure 11.3c, d). Since accurate temperature moni-
toring and feedback control is provided, complex beam forming
and electronic scanning for a series of “macro shot” sequences
can be applied to sonicate over larger volumes and without cool-
ing intervals to produce larger contiguous lesions more quickly,
compared to current configuration of US guided systems.
rotating) have been developed and evaluated
in vivo
and dem-
onstrated significant potential for delivering controlled thermal
ablation to the prostate gland for possible treatment of BPH and
cancer [48-54], and can be integrated with MR temperature
monitoring for treatment control and assessment [55, 56]. The
general configuration of these devices currently under investi-
gation consists of catheters or rigid devices placed within the
urethra with 4-6.4 mm diameter delivery catheters and 2.5 mm
to 4 mm wide by 2-3 cm long transducer arrays that would be
positioned directly within the prostatic urethra. Techniques and
devices have also been investigated for dual frequency operation
to control penetration depth and treatment duration. The most
extensive development of a transurethral applicator, including
recent clinical evaluation in a pilot study, has been performed
specifically for a planar array configuration; this ultrasound
applicator couples rotation of the transducer array with MR tem-
perature feedback to precisely sweep out a conformal thermal
ablation zone along predefined boundaries [56,57]. The appli-
cator configuration consisted of 4-5 transducer sections (3.5
mm × 5 mm long segments, operating at 8-9 MHz), mounted
within a rigid plastic and brass 6.4 mm delivery applicator
(Figure 11.4). Temperature regulated cooling water is circulated
11.3 transurethral Devices
for prostate therapy
Transurethral ultrasound applicators in various configurations
(tubular, planar, and curvilinear transducer arrays; stationary or
