Introduction to Medical Imaging-new gives a basic knowledge

BY Dr Nebyu Samuel
Radiologist
Introduction to Medical Imaging

Radiology
• Diagnostic Imaging
• Interventional Radiology

List of diagnostic imaging studies
 Plain x-rays
 Mammography
 Angiography
 Fluoroscopy
 CT scan
 Nuclear imaging/PET
 MRI
 Ultrasound
 Which of these modalities use
ionizing radiation?

Electromagnetic Spectrum(Radiation)

Diagnostic Imaging
• Electromagnetic Radiation
– Radiography & Computed Tomography (CT)
– Magnetic Resonance Imaging (MRI)
– Nuclear Scintigraphy
(Nuclear Medicine)
• Sound Waves (exception)
– Ultrasound

Types of Radiation
Electromagnetic Radiation (photons)
 Radio frequency – from coils used in MRI
 X-Rays - from xray tube
 Gamma rays - from nuclear decay

Xray
• Plain Radiography
– X RAY PRODUCTION
– inherent contrast
– film
– digital
• Contrast Radiography
– barium
– iodine
• Fluoroscopy
• CT (Computed Tomography)

 X-rays pass through patient to a
receptor (film, digital, fluorescent
screen, etc)
ELECTRONS
XRAYS

January 1896 - First x-ray made in
public
Routine x-ray current technology
Wilhelm Conrad Roentgen
1845-1923

 A diagnostic image is composed of
differences in contrast between tissues!

INHERENT CONTRAST
• Tissue Thickness &
• Tissue Type

Tissue thickness affects x-rays attenuation.
WHITE GRAY BLACK
Tissue Thickness
LESS GET THROUGH>>MORE GET THROUGH

The tissue type affects the attenuation of the x-rays
BLACK GRAY WHITE
Tissue type
MORE GET THROUGH >> LESS GET THROUGH

• Radiographs are summation of shadows created by differences in contrast
between tissues.
• Tissue thickness and tissue composition affect the attenuation and
therefore, the shade(s) of gray in the final shadow image.

Xray
– X ray production
– INHERENT CONTRAST
– film
– digital / PACS
– barium
– iodine
• Fluoroscopy

INHERENT CONTRAST
5 Basic Radiographic Densities
• Tissue
–
–
–
–
–
Air
Fat
Soft Tissues
Bone, Calcium
Metal
• Appearance on XRAY
–
–
–
–
–
Black
Dark Gray
Gray
White
Really White

5 Basic Radiographic Densities
 Air
 Fat
 Soft tissue/fluid
 Mineral
 Metal
1.
2.
3.
4.
5.
Name these radiographic densities.

Xray
– FILM
– digital / PACS
– barium
– iodine
• Fluoroscopy

Film Radiography
FILM CASSETTE

Film Radiography
PHOTONS PRODUCED BY
XRAYS HITTING A SCREEN
IN FRONT OF THE FILM
INSIDE OF A CASSETTE

Xray
– film Radiography
– DIGITAL Radiography
– barium
– iodine
• Fluoroscopy

‘Digital’ Radiography
• Two types
– Computed radiography, called CR
• Film cassette is replaced with a charged metal plate
• After exposure, plate is ‘read’ in a special device
– Digital radiography, called DR
• Film cassette is replaced by a charged sensor (like in a
digital camera or video camera)

Computed Radiography (CR)
HERE ARE
THE PLATES

Film --> Computer Viewing
20TH CENTURY 21ST CENTURY

Contrast Agent
• Anything that enhances the differences between tissues
of similar densities
• For XRAY contrast agents :
– Barium
– Iodine
• Various ways they are introduced
–
–
–
–
Swallowed: barium swallow, upper GI
Per rectum: barium enema
In vein: Intravenous urogram
In artery: Arteriogram

PLAIN
RADIOGRAPH
OF THE CHEST
BARIUM
SWALLOW

PLAIN RADIOGRAPH
OF THE ABDOMEN
BARIUM ENEMA

Iodine:
Intravenous urogram
Intravenous pyelogram
(IVU or IVP)
KIDNEYS
URETERS
BLADDER

Iodine:
Arteriogram through
a catheter (tube)
in the leg
RENAL ARTERY
AORTA
ILIAC ARTERY

Xray
– film
– digital / PACS
– barium
– iodine
• FLUOROSCOPY

Fluoroscopy relies on
image intensifiers to make
moving (real time) X-ray pictures
XRAYS IN LIGHT OUT

Diagram of
fluoroscopic unit
Photograph of a
fluoroscopic unit

Xray
– film
– digital / PACS
– barium
– iodine
• Fluoroscopy
• CT (COMPUTED TOMOGRAPHY)

• Uses X-RAYS
• Tube & Detector spins together around the patient Computer performs
calculations to estimate density of tissues in each square of a ‘slice’
Computed Tomography (CT)
Brain Image 1974, Matrix 80 x 80

What is displayed in CT images?
 CT value; in honor of inventor of CT
(Hounsfeild unit)(HU) - CT numbers.
 Each pixel has a
number representing
the x -ray attenuation
in the corresponding
voxel

Cont…
 Water and water equivalent tissue (0HU)
 Air corresponds (-1000HU).
 Tissues denser than water are given positive CT
numbers.
 The Hounsfield scale has no upper limit.but; for
medical application (-1024HU to +3071HU)

Windowing
 4096 gray levels cannot be differentiated in
single view.
 Human eye can only distinguish max. of 60-80
gray levels.
CT value of interest - window!
 Values above the chosen window - white
 Values below the window - black

Cont…
For display of very small attenuation
differences as given in;
e.g. Brain - Narrow Window is chosen.
For large differences as presented by the
lung or skeleton - Wide Window.

Contrast for CT
• Iodine injected into an arm vein
• Iodine or Barium diluted in water given orally
for abdomen scans
• There are some risks
– Allergic reaction
– Kidney damage
• Enhances the blood vessels and organs

The three orthogonal
views
 In principle slice image can
be generated in arbitrary
orientation.
 However; for CT mostly a
transverse (x/y plane) is
scanned directly
 Z-axis - perpendicular scan
plane
 Sagittal body sections (left /
right) & coronal sections
(ant /post).

Things we can do with CT
image processing
• CT Angiography
Scan rapidly during Iodine injection in vein
• Colonography
Scan colon after filling with air
• Bronchoscopy
Scan chest air is already in bronchi
• 3D Images
Computer reconstruction

Human Responses to Ionizing
Radiation

Human Radiation Response
 effect of x-rays is the result of interactions at the
atomic level
 atomic interactions take the form of ionization
or excitation of orbital electrons and result in
the deposition of energy in tissue

Cont…
 The abnormal molecule in time
- function improperly
- cease to function or death of cell
 At each stage in the sequence, it is possible to
repair radiation damage and recover.

Cont…
 radiation response occurs within minutes or
days after exposure, it is classified as an early
effect of radiation.
 On the other hand, if the human injury is not
observed for months or years, it is called a late
effect of radiation.

Cont…
 Most human responses have been observed to
occur after exposure to rather large radiation
doses.
However, we are cautious and assume that
even small doses are harmful.

• Radio-sensitivity varies with age.
Experiments with animals have shown that the very young and the very old
are more sensitive to radiation.

EARLY EFFECTS OF RADIATION ON
HUMANS
1. Acute radiation syndrome
a.Hematologic syndrome
b.Gastrointestinal syndrome
c.Central nervous system syndrome
2. Local tissue damage
d.Skin
e.Gonads
3. Hematologic depression

LATE EFFECTS OF RADIATION
ON HUMANS
1. Leukemia
2. Other malignant disease
a.Bone cancer
b.Lung cancer
c.Thyroid cancer
d.Breast cancer
3. Local tissue damage
e.Skin
f. Gonads
g.Eyes
4. Shortening of life
span
5. Genetic mutation

Effects of Fetal Irradiation
1.Prenatal death
2.Neonatal death
3.Congenital malformation
4.Childhood malignancy
5.Diminished growth and
development

 The Commandments of Radiation Protection
1. Understand and apply the cardinal principles of
radiation control: time, distance, and shielding.
2. Do not allow familiarity to result in false security.
3. Never stand in the primary beam.
4. Always wear protective apparel when not behind a
protective barrier.
5. Always wear an occupational radiation monitor and
position it outside the protective apron at the collar.
6. Never hold a patient during radiographic examination.
Use mechanical restraining devices when possible.
Otherwise, have parents or friends hold the patient.

Cont…
7. The person who is holding the patient must always
wear a protective apron and, if possible, protective
gloves.
8. Use gonadal shields on all people of childbearing
age when such use will not interfere with the
examination.
9. Examination of the pelvis and lower abdomen of a
pregnant patient should be avoided whenever
possible especially during the first trimester.
10. Always collimate to the smallest field size
appropriate for the examination

• Comparisons of Effective Dose

Magnetic Resonance Imaging
(MRI)

• Starts with a really strong magnet
– Supercooled with Liquid Helium / Nitrogen
• Transmit radio wave pulses into patient
• Listen for return radio waves caused by
interaction with protons (water) in the
patient’s body
• Process the frequency and phase of the
returned signals by computer

 Starts with a really strong magnet
– Supercooled with Liquid Helium / Nitrogen
 Transmit radio wave pulses into patient
 Listen for return radio waves caused by interaction
with protons (water) in the patient’s body
 Process the frequency and phase of the returned
signals

MRI Contrast
 Gadolinium solution injected into vein
 Gadolinium alters the interaction of radio
waves with the protons in water so that it
gives MORE signal
 Shows up as white on images

Magnetic Resonance Angiography
 May be done after injecting contrast (Gadolinium) or
without(TOF)
 Flowing blood changes the way that radio waves
interact with the water in blood
– May give more signal (IN TOF)
– May give less signal (AS FLOW VOID)

Ultrasound
• Uses high frequency sound
– 2-15 MHz typically used
• The sound is produced and detected
with the same device: TRANSDUCER
• Transducer
– Speaker: sound into patient
– Microphone: sound coming back from
patient
Ultrasound uses sound
waves.
Audible 20Hz and 20
000Hz.
Infra sound < 20Hz
Ultrasound > 20 000Hz

Cont…
 The frequency affects the
image QUALITY
 The HIGHER the
frequency, the BETTER
the resolution
 The LOWER the frequency,
the LESS the resolution but
good penetration

Reflected Echo’s
Strong Reflections = ‘Echogenic’ - White
(Diaphragm, tendons, bone)

Reflected Echo’s
Weaker Reflections = Grey
Most solid organs,
thick fluid – ‘isoechoic’
Homogeneous

Reflected Echo’s
No Reflections = Black
(Fluid within a cyst, urine, blood)
‘Anechoic’ or echo-free

• Color Flow Imaging
• The direction of
blood flow is
indicated by the
display color
• Flow is from left to right on the image,
• It is directed toward the transducer on the left-
hand side of the image and away from the
transducer on the right-hand side.

Angiography And
Interventional Radiology

Interventional Radiology
• Needles for biopsy or fluid removal
• Catheters to make angiograms
• Catheters with balloons to open blood vessels
• Stents to hold blood vessels open
• Coils and material to block blood vessels
• Catheters to drain abscesses
• Tubes for feeding
Etc…

Angiogram of normal kidney
SPINE
THIS IS THE
CATHETER
COMING
UP FROM
THE LEG
ARTERY
11TH RIB

Angiogram of renal Cancer
THIS IS THE
MALIGNANT MASS

THIS IS THE
CANCER MASS
Angiogram of artery to mass
THIS IS THE
CATHETER
COMING
UP FROM
THE LEG
ARTERY

Angiogram after embolization
NO BLOOD
FLOW TO
THE MASS
NOW IT CAN
BE REMOVED
WITHOUT
EXCESSIVE
BLEEDING

Angioplasty Balloon
Vascular Stent

BEFORE
Angioplasty & Stent
AFTER

Introduction to Medical Imaging-new gives a basic knowledge

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