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MEDICAL IMAGING

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Title: MEDICAL IMAGING


1
MEDICAL IMAGING
  • Dr. Hugh Blanton
  • ENTC 4390

2
  • There has been an alarming increase in the number
    of things I know nothing about!

3
Lecture 1
  • INTRODUCTION

4
INTRODUCTION TO MEDICAL IMAGING
  • Medical imaging of the human body requires some
    form of energy.
  • In radiology, the energy used to produce the
    image must be capable of penetrating tissues.
  • The electromagnetic spectrum outside the visible
    light region is used for
  • x-ray imaging,
  • magnetic resonance imaging, and
  • nuclear medicine.
  • Mechanical energy, in the form of high-frequency
    sound waves, is used in ultrasound imaging.

5
INTRODUCTION TO MEDICAL IMAGING
  • With the exception of nuclear medicine, all
    medical imaging requires that the energy used to
    penetrate the bodys tissues also interact with
    those tissues.
  • Absorption,
  • Attenuation, and
  • Scattering.

6
INTRODUCTION TO MEDICAL IMAGING
  • If energy were to pass through the body and not
    experience some type of interaction (e.g.,
    absorption, attenuation, scattering),
  • then the detected energy would not contain any
    useful information regarding the internal
    anatomy, and
  • thus it would not be possible to construct an
    image of the anatomy using that information.

7
INTRODUCTION TO MEDICAL IMAGING
  • In nuclear medicine imaging, radioactive agents
    are injected or ingested, and it is the metabolic
    or physiologic interactions of the agent that
    give rise to the information in the images.

8
  • The power levels used to make medical images
    require a balance between patient safety and
    image quality.

9
History, Basic Principles, Modalities
  • Class consists of
  • Deterministic Studies
  • - distortion
  • - impulse response
  • - transfer functions
  • All modalities are non-linear and space variant
    to some degree.
  • Approximations are made to yield a linear,
    space-invariant system.
  • Stochastic Studies
  • SNR (signal to noise ratio) of the resultant
    image
  • - mean and variance

10
Wilhelm Röntgen, Wurtzburg
  • Nov. 1895 Announces X-ray discovery
  • Jan. 13, 1896 Images needle in patients hand
  • X-ray used presurgically
  • 1901 Receives first Nobel Prize in Physics
  • Given for discovery and use of X-rays.

Radiograph of the hand of Röntgens wife, 1895.
11
Röntgens Setup
  • Röntgen detected
  • No reflection
  • No refraction
  • Unresponsive to mirrors or lenses
  • His conclusions
  • X-rays are not an EM wave
  • Dominated by corpuscular behavior

12
Projection X-Ray
attenuation coefficient
Measures line integrals of attenuation
Film shows intensity as a negative ( dark areas,
high x-ray detection
  • Disadvantage Depth information lost
  • Advantage Cheap, simple

13
Sagittal
Coronal
14
Body Structure
15
Directional Terms
  • Anatomical position
  • Beginning reference point
  • Body upright
  • Facing front
  • Arms at side, palms forward
  • Feet parallel

16
Directional Terms
17
Planes of Division
  • Frontal plane
  • Coronal plane
  • Divides body into anterior, posterior parts

18
Planes of Division
  • Sagittal plane
  • Divides body into right, left portions
  • If plane cuts midline, called midsagittal or
    medial plane

19
Planes of Division
  • Transverse plane
  • Divides body into superior, inferior parts

20
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21
Anatomical Directions
  • Anterior (ventral) toward front of body
  • Posterior (dorsal) toward back of body
  • Medial toward midline of body
  • Lateral toward side of body
  • Proximal nearer to reference point
  • Distal farther from reference point

22
Body Cavities
  • Dorsal cavity contains
  • Cranial cavity
  • Spinal cavity

23
Body Cavities (contd)
  • Ventral cavity contains
  • Thoracic cavity
  • Diaphragm
  • Separates
  • thoracic cavity and
  • abdominal cavity

24
Body Cavities (contd)
  • Abdominopelvic cavity
  • Abdominal cavity
  • Pelvic cavity
  • Peritoneum

25
Body Regions
  • Imaginarily divided into 9 regions

26
Body Regions
  • Midline sections
  • Epigastric above stomach
  • Umbilical umbilicus or navel
  • Hypogastric below the stomach

27
Body Regions (cont)
  • Lateral sections
  • Right and left hypochondriac
  • Positioned near ribs, specifically cartilages

28
Body Regions (cont)
  • Right and left lumbar
  • Positioned near small of back (lumbar region)

29
Body Regions (cont)
  • Right and left iliac
  • Named for upper bone of hip (ilium)
  • Also called inguinal region (referring to groin)

30
Body Positions
  • Anatomical
  • Standing erect, facing forward, arms at sides,
    palms forward, toes pointed forward
  • Prone
  • Lying face down
  • Supine
  • Lying face up

31
X-Ray
32
Early Developments
  • Intensifying agents, contrast agents all
    developed within several years.
  • Creativity of physicians resulted in significant
    improvements to imaging.
  • - found ways to selectively opacify regions of
    interest
  • - agents administered orally, intravenously, or
    via catheter

33
Later Developments
  • More recently, physicists and engineers have
    initiated new developments in technology, rather
    than physicians.
  • 1940s, 1950s
  • Background laid for ultrasound and nuclear
    medicine
  • 1960s
  • Revolution in imaging ultrasound and nuclear
    medicine
  • 1970s
  • CT (Computerized Tomography)
  • - true 3D imaging
  • (instead of three dimensions crammed into
    two)
  • 1980s
  • MRI (Magnetic Resonance Imaging)
  • PET ( Positron Emission Tomography)

34
Computerized Tomography (CT)
Result
  • 1972 Hounsfield announces findings at British
    Institute of Radiology
  • Hounsfield, Cormack receive Nobel Prize in
    Medicine
  • (CT images computed to actually display
    attenuation coefficient m(x,y))
  • Important Precursors
  • 1917 Radon Characterized an image by its
    projections
  • 1961 Oldendorf Rotated patient instead of
    gantry

35
First Generation CT Scanner
  • Acquire a projection (X-ray)
  • Translate x-ray pencil beam and detector across
    body and record output
  • Rotate to next angle
  • Repeat translation
  • Assemble all the projections.

36
Reconstruction from Back Projection
1.Filter each projection to account for sampling
data on polar grid 2. Smear back along the line
integrals that were calculated by the detector.
37
Modern CT Scanner
From Webb, Physics of Medical Imaging
38
Computerized Tomography (CT), continued
Early CT Image
Current technology
39
Inhalation
40
Exhalation
41
Nuclear Medicine
  • - Grew out of the nuclear reactor research of
    World War II
  • Discovery of medically useful radioactive
    isotopes
  • 1948 Ansell and Rotblat Point by point
    imaging of thyroid
  • 1952 Anger First electronic gamma camera
  • Radioactive tracer is selectively taken up by
    organ of interest
  • Source is thus inside body!
  • This imaging system measures function
    (physiology)
  • rather than anatomy.

42
Nuclear Medicine, continued
  • Very specific in imaging physiological function -
    metabolism
  • - thyroid function
  • - lung ventilation inhale agent
  • Advantage Direct display of disease process.
  • Disadvantage Poor image quality ( 1 cm
    resolution)
  • Why is resolution so poor?
  • Very small concentrations of agent used for
    safety.
  • - source within body
  • Quantum limited
  • CT 109 photons/pixel
  • Nuclear 100 photons/pixel
  • Tomographic systems
  • SPECT single proton emission computerized
    tomography
  • PET positron emission tomography

43
Combined CT / PET Imaging
44
Comparison of Modalities
  • Why do we need multiple modalities?
  • Each modality measures the interaction between
    energy and biological tissue.
  • - Provides a measurement of physical properties
    of tissue.
  • - Tissues similar in two physical properties
    may differ in a third.
  • Note
  • - Each modality must relate the physical
    property it measures to normal or abnormal
    tissue function if possible.
  • - However, anatomical information and knowledge
    of a large patient base may be enough.
  • - i.e. A shadow on lung or chest X-rays is
    likely not good.
  • Other considerations for multiple modalities
    include
  • - cost - safety - portability/availabili
    ty

45
X-Ray
  • Measures attenuation coefficient
  • Safety Uses ionizing radiation
  • - risk is small, however, concern still
    present.
  • - 2-3 individual lesions per 106
  • - population risk gt individual risk
  • i.e. If exam indicated, it is in your
    interest to get exam
  • Use Principal imaging modality
  • Used throughout body
  • Distortion X-Ray transmission is not distorted.

46
Ultrasound
  • Measures acoustic reflectivity
  • Safety Appears completely safe
  • Use Used where there is a complete soft tissue
    and/or fluid path
  • Severe distortions at air or bone interface
  • Distortion
  • Reflection Variations in c (speed) affect
    depth estimate
  • Diffraction ? desired resolution (.5 mm)

47
Magnetic Resonance (MR)
  • Multiparametric
  • M(x,y,z) proportional to ?(x,y,z) and T1, T2.
  • (the relaxation time constants)
  • Velocity sensitive
  • Safety Appears safe
  • Static field - No problems
  • - Some induced phosphenes
  • Higher levels - Nerve stimulation
  • RF heating body temperature rise lt 1C -
    guideline
  • Use
  • Distortion Some RF penetration effects
  • - intensity distortion

48
Clinical Applications - Table
Chest Abdomen Head
X-Ray/ CT widely used CT - excellent needs contrast CT - excellent X-ray - is good for bone CT - bleeding, trauma
Ultrasound no, except for heart excellent problems with gas poor
Nuclear extensive use in heart Merge w/ CT PET
MR growing cardiac applications minor role standard
49
Clinical Applications - Table
Cardiovascular Skeletal / Muscular
X-Ray/ CT X-ray Excellent, with catheter-injected contrast strong for skeletal system
Ultrasound real-time non-invasive cheap but, poorer images not used
Nuclear functional information on perfusion functional - bone marrow
MR getting better High resolution Myocardium viability excellent
50
Economics of modalities
  • X-Ray Cheapest
  • Ultrasound 100K 250K
  • CT 400K 1.5 million (helical scanner)
  • MR 350K (knee) - 4.0 million
  • Service Annual costs
  • Hospital must keep uptime
  • Staff Scans performed by technologists
  • Hospital Income Competitive issues
  • Significant
    investment and return
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