Biomedical Engineering Reference
In-Depth Information
Bile duct
Esophagus
FIGURE 11.7
Intraluminal ultrasound devices with rotating planar transducers for endoscopic insertion and treatment within the biliary ducts
and direct insertion within the esophagus for thermal ablation. (Courtesy of Drs. David Melodelima, Frederic Prat, and Cyril Lafon of Inserm,
Lyon, France.)
the frequency of an interstitial planar transducer applica-
tor to be varied dynamically to adjust the depth of thermal
coagulation [80]. In contrast to the sectored tubular interstitial
devices, these applicators produce narrow heating fields and rely
on mechanical rotation of the ultrasound source to “sweep” out
a larger treatment field that can conform to a predetermined
outer boundary.
Ex vivo
and
in vivo
testing of these devices
have yielded single-shot thermal lesions extending up to a radial
depth of 10-20 mm, and can sweep out 360° coagulation zones
in 5 minutes [79]. Intraductal or intraluminal high-intensity
ultrasound devices have been configured with a rotating planar
transducer segment (2.8 mm wide × 8 mm long, 10 MHz, 14 W/
cm
2
intensity) at the distal end of a 4 mm flexible catheter [76],
as shown in Figure 11.7. The transducer portion is covered with
a coupling membrane that is inflated and water cooled when
deployed. The device is specific for deployment from the work-
ing channel of an endoscope, which can be positioned under
fluoroscopic guidance within tumor obstruction of the bile duct.
This endoscopic device has been evaluated in a human pilot
study with 10 patients, where varying applied power levels and
rotation position were used to shape the thermal lesion greater
than 10 mm radius over 360° at the site of treatment [81] and
provide relief of obstructions with no adverse events reported.
Similar applicator structures have also been demonstrated for
interstitial ablation of deep-seated targets [4], with the possibil-
ity of using dual-mode arrays to both deliver and monitor the
conformal thermal ablation [82].
Larger diameter (10 mm) applicators (Figure 11.7), based
upon rotating planar (8 mm wide × 15 mm long) transduc-
ers, have been devised for direct insertion into the esophagus
for treatment of esophageal cancer and palliation of associated
strictures. The standard treatment protocol [83] was for device
placement and positioning using fluoroscopy (Figure 11.7c),
then 20 short sequential ablations with 18° rotation between
them were applied for circumferential ablation; if sections of
esophagus greater than ~15 mm were required to be treated,
then the applicator was repositioned in a linear fashion and the
process repeated for further treatment. This clinical pilot study
demonstrated feasibility of the approach; the endogastric ultra-
sound applicator could induce localized tumor necrosis within
the esophageal stricture, and can provide symptomatic improve-
ment. More recent advanced phased arrays and MR compatible
devices suitable for MR guided procedures with fast MR tem-
perature monitoring are under evaluation [84,85] and indicate
potential for precision MR directed ablations within esophagus
and biliary ducts, or other similarly accessible sites.
11.5 Summary
Ultrasound technology has many advantages over other modali-
ties and devices as currently applied for interstitial and intra-
cavitary thermal therapy for the treatment of cancer. Given the
ability to integrate small or focused transducers within these
applicators, and the enhanced penetration and spatial control of
energy, these devices can afford precise and accurate delivery of
thermal ablation and hyperthermia. Furthermore, these devices
can be combined with ultrasound or MR imaging to dramatically
improve targeting, treatment control, and treatment verification.
Although not covered herein, there are many investigations cur-
rently underway to continue miniaturization and customization
of ultrasound devices for site-specific treatment in other areas of
interest. Many of the devices discussed herein provide a powerful
tool that can be used for conformal thermal ablation therapy or
hyperthermia, either alone or concurrent with chemotherapy or
radiation therapy, or with thermally mediated drug delivery.
references
1. Diederich, C.J. and K. Hynynen, Ultrasound technology for
hyperthermia.
Ultrasound in Medicine and Biology
, 1999.
25
(6): p. 871-887.
2. ter Haar, G., Ultrasound focal beam surgery.
Ultrasound in
Medicine and Biology,
1995.
21
(9): p. 1089-100.
3. Ahmed, M., C.L. Brace, F.T. Lee, Jr., and S.N. Goldberg,
Principles of and advances in percutaneous ablation.
Radiology
, 2010.
258
(2): p. 351-69.
4. Lafon, C., D. Melodelima, R. Salomir, and J.Y. Chapelon,
Interstitial devices for minimally invasive thermal abla-
tion by high-intensity ultrasound.
Int J Hyperthermia,
2007.
23
(2): p. 153-63.
5. Ryan, T.P., P.F. Turner, and B. Hamilton, Interstitial micro-
wave transition from hyperthermia to ablation: Historical
perspectives and current trends in thermal therapy.
Int J Hyperthermia,
2010.
26
(5): p. 415-33.
