MR guided Focused Ultrasound Surgery MRgFUS for Uterine Fibroids

Focused Ultrasound (FUS)
MR guided Focused
Ultrasound Surgery
MRgFUS for Uterine
Fibroids
•The ExAblate 2000 system is a device that can
target and ablate tissue without requiring
surgical incision
Abdullah BJJ,
Department of Biomedical Imaging,
University of Malaya, Kuala Lumpur,
Malaysia
How Focused Ultrasound Works
•
•
•
A sound wave is a mechanical disturbance that induces
oscillatory motion in particles of a medium.
Diagnostic ultrasound produces internal organ pictures
by exposing the body to high-frequency sound waves.
Ultrasound therapy uses lower frequencies with
significantly higher intensities.
How Focused Ultrasound Works
(con’t)
•Similar to how a magnifying glass focuses
light energy, ultrasound can be focused on a
specific point
Treated
spot
Tumor
Transducer
Energy
pass zone
Ultrasound Effect on Tissue
•
•
•
Focused Ultrasound Transducer
When ultrasound waves propagate in tissue, the
energy is absorbed and converted to molecule
movement that generates heat
• A phased array transducer electronically
adjusts the focal location
The highest temperature increase is at the focus, since
this is where the sound waves converge and have the
highest energy
density
In the beam pass
zone the energy
density is low
hence the
temperature
increase is low
ls
igna
RF S
Multi-element
phased array
transducer
Tissue heating
40
50
60
70
80
1
Ultrasound Effect on Tissue
• Thermal simulations show the shape of the
focus
Thermal Therapy
When tissue is heated
and exceeds a certain
thermal dose threshold,
tissue ablation occurs
• Thermal dose of 100%
tissue ablation*:
• At 43oC – 240 minutes
• Or at 54oC – 3 second
• Or at 57oC – 1 second
Parallel to beam path
Total ablation
Perpendicular to beam path
*Sapareto SA, Dewey WC. Thermal dose determination in cancer therapy
Physiology of Thermal Therapy
•Coagulated regions
seen in macro
pathology image
MRgFUS treated liver (pig)
•Histology analysis
shows a sharp
demarcation between
treated and non
treated regions
Uterine fibroids
• Most common tumors on
women over the age of
30
• High prevalence
• Most common indication
for hysterectomy
• Hysterectomy annual
costs in US in excess of
$2 billion
• (Zhao, 1999)
• Lost productivity due to
menorrhagia
$1692/woman/year
• (Cote 2002)
0.1 mm
2
MRgFUS
Two technologies combined:
•
Focused ultrasound beam to ablate the specific
tissue
•
MR imaging and thermal
mapping system for
visualization of patient
anatomy and feedback
on tissue temperature
during the treatment
MRI
MR Imaging Anatomy
•
Magnetic Resonance Imaging (MRI) is a method used
to visualize the inside of living organisms.
•
MRI uses non-ionizing, radio frequency signals to
acquire images. MRI is best suited for soft (noncalcified) tissues.
•
Medical MRI relies on the relaxation properties of
excited hydrogen nuclei in water and fat.
Ribs
Nerves
Uterus
Fibroid
Breast
Tumor
Bladder
Pubic bone
T1W+C breast MR image
T2W pelvic MR image
MR Thermometry
MR Guidance
•Provides real-time feedback during treatment, showing regions that
have met thermal dose requirements
•Visualization of treatment plan
before energy is delivered,
identifies:
Bowel
Nerves
Surgical clips
6 sec
12 sec
18 sec
Parallel to
beam path
+
+
+
24 sec
+
Perpendicular
to beam path
+
+
+
+
Temperature
graph
sonicating
cooling
Scar
3
Patient Table
Patient Table (con’t)
• The table consists of
front end electronics,
and a cradle with the
FUS transducer
Transducer
•
The phased array
transducer is
housed in a
sealed water bath
•
The transducer is
connected to a
robotic positioner
cradle
Electronics
storage
Robotic
positioner
• The patient
table docks to
the GE MR
scanner
Power cable
Treatment Evaluation
•
Pre-treatment screening
NPV ratio is the Non Perfused Volume (immediately post
treatment) divided by the Total Fibroid Volume.
•
High NPV ratio was found to be related to:
•
SSS (Symptoms Severity Score, from the QOL
questionnaire) improvement.
•
Low number of alternative treatments (in follow up).
•
Fibroids shrinkage (in follow up).
30%
90%
Purpose
• Identification of fibroids
• Type, number and size
• Position of organs, bowel and nerves
• Accessibility of fibroids
• Scars on abdominal wall
Pre-treatment screening
Procedure for screening MRI
• T2WI in 2 planes (anatomy + pathology)
• T1WI in one plane with and without
contrast (for viability)
• Use screening pad
• Feet in first
• Patient bladder should be empty
Exclude patients that
•
•
•
•
•
•
•
Are younger than 18 yrs
Are post menopausal
Are pregnant or seek for future pregnancies
Have serious health complications
Have contraindications to MRI
Uterine size is more than 24 weeks
Have massive abdominal scarring in the pass zone (e.g. from
laparotomy)
• Have been previously treated with Uterine Artery Embolization
(UAE)
4
MR Screening (1)
• Perform MRI screening prior to the
treatment to check the accessibility,
viability and texture of the fibroid(s).
• Use the images to check the size and
number of fibroid(s)
• MR screening can also reveal other
uterine disorders that cannot be treated
with MRgFUS, such as adenomyosis.
MR Screening (2)
•
Screening procedure:
• Position patient prone. Perform 2 plane T2w imaging (for
anatomy and pathological conditions) and T1w imaging
with and without contrast agent (to identify fibroid’s
viability)
Recommendation:
•Screen the patient with empty
bladder.
•Use the ExAblate table, with the 4cm
screening pad. Alternatively, use the
1cm screening pad on the MR table.
Accessibility (1)
Bowels should not be present in the
beam path, as it may contain of air
or energy absorbing particles.
Accessibility (2)
Refrain from other
obstacles on the
beam path, as:
No
No
•IUD
• Surgical clips
•
•
No access
• Surgical scars
Yes
Full access
•
Limited access
Accessibility (3)
•
12 cm from the skin is the
maximal effective focal
distance of the system.
•
Exclude patient with a
significant deeper fibroid
portion.
Viability
12 cm
Non-enhancing
Partly enhancing
Enhancing
Non-enhancing on T1W with contrast are not viable, thus
the treatment will have no additional benefit
5
Texture
Viability
Non-enhancing
Partly enhancing
Enhancing
Non-enhancing on T1W with contrast are not viable, thus
the treatment will have no additional benefit
Dark
Bright
Bright fibroids on T2w images (relative to the uterus
wall) are less susceptible to the treatment
Size and number
Adenomyosis
• both adenomyosis and leiomyomas
commonly coexist; concomitant
adenomyosis
• in hysterectomy specimens of women with
leiomyomas ranges from 15 to 57%
Don’t treat patients with
5 or more symptomsrelated fibroids
•Total fibroid load
should be less
than 500 cc per
treatment
Adenomyosis
Efficiency of treating adenomyosis
has not yet been proven in clinical
trials; there is anecdotal evidence.
Treatment Cycle
Sonication
Cooling
Sonication
MR Scans
Fetch Images
Monitor sonication
Compute Dose
Review Results
Adenomyosis during
menstruation
6
Treatment Evaluation
Accumulated
Dose
Coronal planning image
with accumulated dose
overlay
•
•
•
•
Treated region
(Non-Perfused
Volume, NPV)
Coronal image of posttreatment MRI with contrast
There were no life-threatening adverse events in either group.
Overall, the number of significant clinical complications and adverse
events was lower in women in the MRgFUS group compared to
women undergoing hysterectomy.
MRgFUS was associated with significantly faster recovery, including
resumption of usual activities.
Women undergoing MRgFUS had steady improvement in all
parameters throughout the 6-month follow-up period, despite the
fact that they continued to have myomatous uteri and menstruation,
which at baseline had given them significant symptomatology.
•
•
•
•
•
the non-perfused volume (NPV) ratio in 287 Japanese patients divided into
two equal groups according to the chronological treatment time to estimate
the learning curve effect.
The NPV ratio increased chronologically, from 39.3% to 54.0% (P < 0.001),
indicating increasing effectiveness of the treatment with experience.
The mean NPV ratios for the entire patient population were over double that
of previous clinical trials (46.6% vs. 21.9%; P < 0.001).
No serious complications were reported
The learning process and accumulation of data on MRgFUS enable the
optimization of treatments in order to safely achieve large NPV ratios and
sustained clinical benefit.
Result(s): Fifty-four pregnancies in 51 women have occurred after
MRgFUS treatment of uterine leiomyomas.
The mean time to conception was 8 months after treatment. Live births
occurred in 41% of pregnancies, with a 28% spontaneous abortion rate,
an 11% rate of elective pregnancy termination, and 11 (20%) ongoing
pregnancies beyond 20 gestational weeks. The mean birth weight was
3.3 kg, and the vaginal delivery rate was 64%.
Conclusion(s): Preliminary pregnancy experience after MRgFUS is
encouraging, with a high rate of delivered and
ongoing pregnancies.
7
•
•
•
•
•
•
•
•
Result(s): Fifty-four pregnancies in 51 women have occurred after
MRgFUS treatment of uterine leiomyomas.
The mean time to conception was 8 months after treatment.
Live births occurred in 41% of pregnancies
28% spontaneous abortion rate
11% rate of elective pregnancy termination
20% ongoing pregnancies beyond 20 gestational weeks.
The mean birth weight was 3.3 kg, and the vaginal delivery rate was
64%.
Conclusion(s): Preliminary pregnancy experience after MRgFUS is
encouraging, with a high rate of delivered and ongoing pregnancies.
Fertility and Sterility Vol. 93, No. 1, January
2010 1
8