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MEDICAL IMAGING. Dr. Hugh Blanton ENTC 4390. There has been an alarming increase in the number of things I know nothing about!. Lecture 1. INTRODUCTION. INTRODUCTION TO MEDICAL IMAGING. Medical imaging of the human body requires some form of energy.

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medical imaging


Dr. Hugh Blanton

ENTC 4390

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

Dr. Blanton ENTC 4390 --Introduction 2

lecture 1

Lecture 1


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.

Dr. Blanton ENTC 4390 --Introduction 4

introduction to medical imaging1
  • With the exception of nuclear medicine, all medical imaging requires that the energy used to penetrate the body’s tissues also interact with those tissues.
    • Absorption,
    • Attenuation, and
    • Scattering.

Dr. Blanton ENTC 4390 --Introduction 5

introduction to medical imaging2
  • 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.

Dr. Blanton ENTC 4390 --Introduction 6

introduction to medical imaging3
  • 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.

Dr. Blanton ENTC 4390 --Introduction 7

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

Dr. Blanton ENTC 4390 --Introduction 8

history basic principles modalities
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

Dr. Blanton ENTC 4390 --Introduction 9

wilhelm r ntgen wurtzburg
Wilhelm Röntgen, Wurtzburg

Nov. 1895 – Announces X-ray discovery

Jan. 13, 1896 – Images needle in patient’s 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 Röntgen’s wife, 1895.

Dr. Blanton ENTC 4390 --Introduction 10

r ntgen s setup
Röntgen’s 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

Dr. Blanton ENTC 4390 --Introduction 11

projection x ray
Projection X-Ray

Disadvantage: Depth information lost

Advantage: Cheap, simple



Measures line integrals of attenuation

Film shows intensity as a negative ( dark areas, high x-ray detection

Dr. Blanton ENTC 4390 --Introduction 12




Dr. Blanton ENTC 4390 --Introduction 13

directional terms
Directional Terms
  • Anatomical position
    • Beginning reference point
    • Body upright
    • Facing front
    • Arms at side, palms forward
    • Feet parallel

Dr. Blanton ENTC 4390 --Introduction 15

directional terms1
Directional Terms

Dr. Blanton ENTC 4390 --Introduction 16

planes of division
Planes of Division
  • Frontal plane
    • Coronal plane
    • Divides body into anterior, posterior parts

Dr. Blanton ENTC 4390 --Introduction 17

planes of division1
Planes of Division
  • Sagittal plane
    • Divides body into right, left portions
    • If plane cuts midline, called midsagittal or medial plane

Dr. Blanton ENTC 4390 --Introduction 18

planes of division2
Planes of Division
  • Transverse plane
    • Divides body into superior, inferior parts

Dr. Blanton ENTC 4390 --Introduction 19

anatomical directions
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

Dr. Blanton ENTC 4390 --Introduction 21

body cavities
Body Cavities
  • Dorsal cavity contains:
    • Cranial cavity
    • Spinal cavity

Dr. Blanton ENTC 4390 --Introduction 22

body cavities cont d
Body Cavities (cont’d)
  • Ventral cavity contains:
    • Thoracic cavity
    • Diaphragm
      • Separates
        • thoracic cavity and
        • abdominal cavity

Dr. Blanton ENTC 4390 --Introduction 23

body cavities cont d1
Body Cavities (cont’d)
  • Abdominopelvic cavity:
    • Abdominal cavity
    • Pelvic cavity
    • Peritoneum

Dr. Blanton ENTC 4390 --Introduction 24

body regions
Body Regions
  • Imaginarily divided into 9 regions

Dr. Blanton ENTC 4390 --Introduction 25

body regions1
Body Regions
  • Midline sections:
    • Epigastric = above stomach
    • Umbilical = umbilicus or navel
    • Hypogastric = below the stomach

Dr. Blanton ENTC 4390 --Introduction 26

body regions con t
Body Regions (con’t)
  • Lateral sections:
    • Right and left hypochondriac
    • Positioned near ribs, specifically cartilages

Dr. Blanton ENTC 4390 --Introduction 27

body regions con t1
Body Regions (con’t)
  • Right and left lumbar
    • Positioned near small of back (lumbar region)

Dr. Blanton ENTC 4390 --Introduction 28

body regions con t2
Body Regions (con’t)
  • Right and left iliac
    • Named for upper bone of hip (ilium)
    • Also called inguinal region (referring to groin)

Dr. Blanton ENTC 4390 --Introduction 29

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

Dr. Blanton ENTC 4390 --Introduction 30

early developments
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

Dr. Blanton ENTC 4390 --Introduction 32

later developments
Later Developments

More recently, physicists and engineers have initiated new developments in technology, rather than physicians.

1940’s, 1950’s

Background laid for ultrasound and nuclear medicine


Revolution in imaging – ultrasound and nuclear medicine


CT (Computerized Tomography)

- true 3D imaging

(instead of three dimensions crammed into two)


MRI (Magnetic Resonance Imaging)

PET ( Positron Emission Tomography)

Dr. Blanton ENTC 4390 --Introduction 33

computerized tomography ct
Computerized Tomography (CT)

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


Dr. Blanton ENTC 4390 --Introduction 34

first generation ct scanner
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.

Dr. Blanton ENTC 4390 --Introduction 35

reconstruction from back projection
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.

Dr. Blanton ENTC 4390 --Introduction 36

modern ct scanner
Modern CT Scanner

From Webb, Physics of Medical Imaging

Dr. Blanton ENTC 4390 --Introduction 37

computerized tomography ct continued
Computerized Tomography (CT), continued

Early CT Image

Current technology

Dr. Blanton ENTC 4390 --Introduction 38



Dr. Blanton ENTC 4390 --Introduction 39



Dr. Blanton ENTC 4390 --Introduction 40

nuclear medicine
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.

Dr. Blanton ENTC 4390 --Introduction 41

nuclear medicine continued
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

Dr. Blanton ENTC 4390 --Introduction 42


Combined CT / PET Imaging

Dr. Blanton ENTC 4390 --Introduction 43

comparison of modalities
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.


- 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/availability

Dr. Blanton ENTC 4390 --Introduction 44

x ray1

Measures attenuation coefficient

Safety: Uses ionizing radiation

- risk is small, however, concern still present.

- 2-3 individual lesions per 106

- population risk > 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.

Dr. Blanton ENTC 4390 --Introduction 45


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


Reflection: Variations in c (speed) affect depth estimate

Diffraction: λ ≈ desired resolution (~.5 mm)

Dr. Blanton ENTC 4390 --Introduction 46

magnetic resonance mr
Magnetic Resonance (MR)


M(x,y,z) proportional to ρ(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 < 1˚C - guideline


Distortion: Some RF penetration effects

- intensity distortion

Dr. Blanton ENTC 4390 --Introduction 47

clinical applications table
Clinical Applications - Table

Dr. Blanton ENTC 4390 --Introduction 48

clinical applications table1
Clinical Applications - Table

Dr. Blanton ENTC 4390 --Introduction 49

economics of modalities
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

Dr. Blanton ENTC 4390 --Introduction 50