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

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A PRIMTIVE ANALOGY
ANALOGY FROM Gail R. ter Haar, Royal Marsden
HospitalUnited Kingdom PICTURE FROM
http//wmuma.com/tracker/skills/fire/magnifier/
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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

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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)

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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

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MR GUIDED HIFU SYSTEM
UPPER PICTURE SOURCE http//www.insightec.com LEF
T 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.
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MR GUIDED TEMP CONTROL
UPPER PICTURE SOURCE http//www.dkfz-heidelberg.d
e/mrphys/temperature/temperature.html LEFT
PICTURE SOURCE MR Imagingguided 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.
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HIFUS TREATMENT TREND

• 1960s Proved to be an effective treatment for
  Parkinsons 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?

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HIFUS 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

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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

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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

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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

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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
  EffectivenessInitial 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
• New and 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/temperat
  ure/temperature.html
• QUESTIONS OR COMMENTS jason.smale_at_utoronto.ca