High intensity focused ultrasound
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HIGH INTENSITY FOCUSED ULTRASOUND. CESO Conference April 29, 2004 Jason Smale Clinical Engineering Student, University of Toronto. A PRIMTIVE ANALOGY. ANALOGY FROM: Gail R. ter Haar, Royal Marsden Hospital:United Kingdom PICTURE FROM: http://wmuma.com/tracker/skills/fire/magnifier/.

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HIGH INTENSITY FOCUSED ULTRASOUND

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High intensity focused ultrasound

HIGH INTENSITY FOCUSED ULTRASOUND

CESO Conference

April 29, 2004

Jason Smale

Clinical Engineering Student,

University of Toronto


A primtive analogy

A PRIMTIVE ANALOGY

ANALOGY FROM: Gail R. ter Haar, Royal Marsden Hospital:United Kingdom

PICTURE FROM: http://wmuma.com/tracker/skills/fire/magnifier/


Advantages of hifu

ADVANTAGES OF HIFU

  • Non-Invasive

    • Preserve tissue integrity

    • Relatively Infection Free

  • Non-Ionizing Treatment

  • Minimal or no anesthesia required

  • Shorter recovery period

  • Shorter treatment time

    • 10-15 sec/treatment point

    • 60-600 sec/treatment point for other hyperthermia treatments

      • laser, RF or water


Limitations of hifu

LIMITATIONS OF HIFU

  • Controlling of the Focal Spot

    • Patient shift or tissue motion

    • Cannot adequately control shape, size or location

  • Beam dosimetry

    • Unknown tissue temperatures

    • Possibility of acoustic cavitation

    • Local tissue thermal conductivity and perfusion

      • Tissue specific

      • Patient specific (Skin thickness, proportion of fat and muscle)

      • Growth specific (Malignant, Benign, and Healthy)


Solutions

SOLUTIONS?

  • Couple With Diagnostic Ultrasound

    • Can monitor focal point position

    • Could not measure tissue temperature

  • Couple With Diagnostic MRI

    • Easily monitor soft tissue focal point

    • Can calculate tissue temperature

      • Proton resonant frequency is dependent of temperature

    • Must use a MRI compatible focused ultrasound system


Mr guided hifu system

MR GUIDED HIFU SYSTEM

UPPER PICTURE SOURCE: http://www.insightec.com

LEFT PICTURE SOURCE: http://www.surgeons.org/asernip-s/net-s/information/mri_guided_focused_ultrasound.htm

RIGHT PICTURE SOURCE: MRI Guided Focused Ultrasound Surgery of Fibroadenomas in the Breast: A Feasibility Study, Hynynen et al.


Mr guided temp control

MR GUIDED TEMP CONTROL

UPPER PICTURE SOURCE: http://www.dkfz-heidelberg.de/mrphys/temperature/temperature.html

LEFT PICTURE SOURCE: MR Imaging–guided Focused Ultrasound Surgery of Uterine Leiomyomas: A Feasibility Study, Tempany et al.

RIGHT PICTURE SOURCE: MRI Guided Focused Ultrasound Surgery of Fibroadenomas in the Breast: A Feasibility Study, Hynynen et al.


Hifu s treatment trend

HIFU’S TREATMENT TREND

  • 1960s – Proved to be an effective treatment for Parkinson’s Disease

    • Outdone by L-Dopa treatment

  • 1980s and 90s – Proved to be an effective eye treatment

    • Outdone by eye-laser treatment

  • 1990s and 2000s– Tumor ablation treatment

    • Hoping to be outdone by a cure for cancer?


Hifu s tumor ablation effectiveness

HIFU’S TUMOR ABLATION EFFECTIVENESS

  • Proven effective treatment for prostate tumors

    • Uses a trans-rectal transducer

  • Investigations are being performed to test safety and efficacy:

    • 9 centers are performing clinical investigations worldwide

      • Phase III Benign Fibroadenomas

        • Paper published Hynynen (BWH)

      • Phase III Benign Uterine Fibroids

        • Paper published by Tempany (BWH)

      • Phase II Breast Cancer

        • Paper published by Gianfelice (St. Luc)

    • General Investigation into Brain Tumor ablation

      • Investigations underway at BWH


Important points from research

IMPORTANT POINTS FROM RESEARCH

  • Patients are released same day

  • Some patients suffered from

    • Skin burns, Abdominal Blistering, Scar Tissue burns

      • Approximately 17% of patients received 2nd degree burns

    • Mild discomfort as tumor site for 24-36 hours following ablation

      • 30% patients rated pain more severe than mild discomfort


Trans skull hifu

TRANS-SKULL HIFU

  • Problems with using HIFU on the brain

    • Heterogeneous thickness and density of the skull

    • Very diverse acoustic velocities of the skull and brain tissue

    • Impedance matching

    • Results in Signal attenuation, overheating of tissue near the skull and requires a high number of transducers

  • Uses CT instead of MR

    • Able to measure heterogeneous internal density of skull

  • The magic of time reversal

    • Virtual source sends “acoustical wave” from focal point and amplitude and delay are calculated at HIFU transducer points

    • Measured signal is sent into the brain to create focal point


Hifu effects on the clinical engineer

HIFU EFFECTS ON THE CLINICAL ENGINEER

  • Future roll of MR Guided HIFU is relatively unknown

  • Similar to lasers – “The solution without a problem”

  • Since reporting on Phase 3 trials for benign tumors, implementation might be just over the horizon for some of the larger hospitals

  • “Its better to lead the technology trend than to follow it.” – A. Dolan, University of Toronto


References

REFERENCES

  • MR Imaging-guided Focused Ultrasound Surgery of Uterine Leiomyomas, Tempany et al., Radiology (226), March 2003

  • MR Imaging-guided Focused Ultrasound Surgery of Fibroadenomas in the Breast, Hynynen et al., Radiology (219), April 2001

  • MR Imaging-guided Focused US Ablation of Breast Cancer: Histopathologic Assessment of Effectiveness—Initial Experience, Gianfelice et al., Radiology (227), June 2003

  • High Intensity Focused Ultrasound for the Treatment of Tumors, Ter Haar, Echocardiography, Volume 18, No. 4, May 2001

  • Newand Emerging Techniques – Surgical Procedure Brief MRI-Guided Focused Ultrasound for Uterine Fibroids, Royal Australasian College of Surgeons, August 2003

  • Tissue Thermal Conductivity by Magnetic Resonance Thermometry and Focused Ultrasound Heating,Cheng et al.,JOURNAL OF MAGNETIC RESONANCE IMAGING (16), 2002

  • Experimental demonstration of noninvasive transskull adaptive focusing based on prior computed tomography scans, Aubry et al., Journal of Acoustical Society of America, January 2003

  • Poster: MR Guided Focused Ultrasound Surgery, R. Newman, Vice President, InSightec TxSonics

  • InSightec Website: www.insightec.com

  • In-vivo MR Temperature Monitoring of Focused Ultrasound (HIFU) in Rabbit Muscle, Rademaker et al., http://www.dkfz-heidelberg.de/mrphys/temperature/temperature.html

    QUESTIONS OR COMMENTS: [email protected]


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