ME 328: Medical Robotics
Winter 2019
Lecture 6:
Medical imaging and
image-guided interventions
Allison Okamura
StanfordUniversity
Updates
Assignment 3
Due this Thursday, Jan. 31
Note that this assignment is purposely somewhat open-ended.This and
the remaining assignments will continue be like “mini projects”.
Tours: Save the dates
Auris Health: Friday, February 22
Intuitive Surgical: Friday, March 1
We will send polls for attendance and drivers. 40 people max. for each.
first, a brief
introduction to
image-guided
procedures
reference: Image-Guided Interventions,
edited by Terry Peters and Kevin Cleary
idealized time-line description
of image-guided procedures
Phase 1: Pre-operative planning
Phase II: Intraoperative plan execution
Phase III: Postoperative assessment
Preoperative Intraoperative
computer-assisted update model update plan
planning
patient-specific real-time
modeling computer
assistance
Postoperative
atlas computer-
assisted
patient database assessment
image guidance enables minimally
invasive procedures
previously:
surgery
now:
a wide variety of specialties exist
for medical interventions, and they
are not all considered “surgery”
(consider cardiology, radiology)
key technologies associated with
image-guided procedures
medical imaging and
image processing replaces vision
data visualization and replaces
image segmentation visual reasoning
registration, replaces
trackingsystems, and hand-eye
human-computer coordination
interaction
Physicians mentallyintegrate their
knowledge of anatomical structures with
patient-specificmedical images to produce
a plan and execute it.
Image-guided systems use a similar
approach, where all information sources
are integratedand used to provide
guidance to the physician.
Image-Guided Procedures:A Review, by Ziv Yaniv and Kevin Cleary (2006)
medical imaging
why use medical images?
intensity values are related to physical tissue
characteristicswhich in turn relate to
(1) anatomical information and/or
(2) a physiological phenomenon
anatomy
physics
physiology
what should you consider when
selecting an imaging modality?
technical specifications:
• spatial resolution
• temporal resolution
• field of view
• types of biological and physiologicinformation
possible interaction between the imaging modality
and intervention (e.g., does a metal robot cause
image artifacts? does the magnet of the MRI
machine cause the robot to malfunction?)
traditional functional
vs.
imaging imaging
physiologic information physiologic information
is interpreted is computed
projection imaging:
• 2D cross images are generatedby capturinga
“view” from a single direction
vs.
tomographic images:
• 3D images are generatedby stacking a set of 2D
crosssectional image slices
• derivedfrom the Greek tomos (slice) and graphein
(to write)
most common types
of imaging modalities
• X - rays: film, digital, fluoroscopy, Digital Subtraction
Angiography(DSA)
• CT: Computed Tomography
• Ultrasound: 2D and 2.5D (stack of slices)
• MRI : Magnetic Resonance Imaging (discussed later)
• Video: laparoscopes and endoscopes (discussed later)
• N M : Nuclear Medicine (not covered)
• PET -- Positron Emission Tomography
• SPECT -- Single Photon Emission Tomography
in the beginning, there was x-ray
physics: densityof x-ray absorption
(x-rays are a form of ionizingradiation)
gray value
on film is
proportional
to radiation
energy
first “medical” x-ray, 1895 http://www.britannica.com/
from film to digital
traditional X-ray film is replaced by solid-state detectors
that convert X-rays into electrical signals (CCD camera)
Advantages:
1. there is no film to process, so the images are available
immediately
2. digital images can be shared or enhanced electronically
3. digital images can be used for computer-assisted detection
(helps doctors confirm or draw more attention to suspicious
areas on a digital image)
4. essential for real-time decision making in robot-assisted
interventions
mammogram machine
uses low-energy X-rays for detection of early cancer (microcalcifications)
common screening method, lately somewhat controversial
traditional configurationsof x-ray
and fluoroscopymachines
early fluoroscope Philips digital multi-
(Britannica Film) functional X-ray system
c-arm fluoroscopy
Philips XperCT (CT-like imaging, more on CT later)
digital subtraction angiography (DSA)
create a pre-contrast image, then subtract it from later
images after a contrast medium has been introduced
iodine and barium are common types of contrast mediums
for x-ray, since they attenuate x-rays (vessels become dark)
discussion
how can robots improve x-ray/
fluoroscopyprocedures?
how can x-ray/fluoroscopybe used in
robotic interventions?
computed tomography (CT scan)
3D images are generatedfrom a large seriesof 2D
X-ray images taken around a single axis of rotation
(producesa volume of data for analysis)
physics: same as x-ray
single slice series of parallel slices 2mm apart
L. Joskowicz Qc 2011
computed tomography (CT scan)
3D images are generatedfrom a large seriesof 2D
X-ray images taken around a single axis of rotation
(producesa volume of data for analysis)
physics: same as x-ray
L. Joskowicz Qc 2011
emitter/receiver configuration
http://www.youtube.com/watch?v=M-4o0DxBgZk
CT machines
two examples from Philips(Brilliance 6 and 40)
differ in number of images per second, number of detectors, etc.
discussion
what challenges might exist in
performing CT-guided robotic
interventions?
ultrasoundimaging (diagnostic)
physics: variationsof acousticimpedance
1. probe sends high-frequencysoundwaves
(1-5 MHz) into the body
2. soundwaves travel into tissue and get
reflected by boundaries
3. reflected waves are recorded by the probe
4. time of flight gives spatial information about
the boundaries
the desiredfrequencyof signal is chosen based
on a trade-off of resolution and attenuation
ultrasound
A - mode (amplitude mode): a single
transducer scans a line through the body with the
echoes plotted on screen as a function of depth.
Therapeutic ultrasound aimed at a specifictumor or
calculus is also A-mode, to allow for accurate focus
of the destructive wave energy.
B - mode (brightness mode) or 2D mode: a
linear array of transducerssimultaneouslyscans a
plane through the body that can be viewedas a
two-dimensional image on screen
common application: fetal ultrasound
images courtesy Nora M. Su
ultrasoundcharacteristics
• No radiation
• Poor resolution (~1mm)
non-uniform, distortion,
noisy
• Low penetration
properties
• One 2D slice or several
slices (2.5D)
• Relativelycheap and easy
to use
• Preoperative and
intraoperative use
L. Joskowicz Qc 2011
ultrasoundmachine
ultrasound transducers/probes
Ultrasonix
http://used-medicalequipmentblog.blogspot.com/
3D ultrasound
reconstruct 3D data from 2D slices
acquisition methods: linear, rotation, fan-like, hand
L. Joskowicz Qc 2011
transrectal ultrasound
prostate brachytherapy
http://www2.cfpc.ca
https://myhealth.alberta.ca/
Doppler ultrasound
employs the Doppler effect to determine whether
structures (typicallyblood) are movingtowards or away
from the probe, and their relative velocity
color and pulsed Doppler of blood shunting across a muscular
ventricular septal defect (in the heart)
http://www.glowm.com/
ultrasoundelastography
ablated
tissue
0 0
Freehand -0.01
10
palpation
depth (mm)
elastograms -0.02
20
-0.03
Boctor, Rivaz, Fleming, 30
Foroughi, Fichtinger, Hager
-0.04
(2008)
0 10 20 30
width (mm)
discussion
what challenges might exist in
performing ultrasound-guided robotic
interventions?
caution!
when introducingrobotic (or any)
technologyinto the interventional suite,
you should consider what imaging
modalitiesare already used and available
there is a conflict between the
potential for improvinga procedure
and the practical limitations in
changing the workflow and resources
required to perform the procedure
Modality Intra-operative Accessability Data
Availability Dimensionality
Computed Tomography (CT) available (not widespread) high 3D
Magnetic Resonance Imaging (MRI) available (not widespread) high 3D
X-ray available high 2D projection
functional Magnetic Resonance
Imaging (fMRI) not available moderate 3D
Positron Emission Tomography (PET) not available moderate 3D
Single Photon Emission
Computed Tomography (SPECT) not available moderate 3D
X-ray Fluoroscopy available high 2D projection
C-arm C T available low 3D
Ultrasound (US) available high 2D
optical imaging available high 2D projection
Table 1: Classification of imaging devices according to their availability for intra-
operative use, their accessability to physicians around the world, the dimensionality
of the data they acquire and the type of information conveyed by the images.
Image-Guided Procedures:A Review, by Ziv Yaniv and Kevin Cleary (2006)
