.
Radiology: a medical specialty uses the imaging to both
diagnose and treat disease visualized within the human
body.
Radiologists use an array of imaging technologies to
diagnose or treat diseases (X-ray radiography, ultrasound,
computed tomography (CT), nuclear medicine, positron
emission tomography (PET) and magnetic resonance imaging
(MRI)).
Interventional radiology: the performance of
(usually minimally invasive) medical procedures
with the guidance of imaging technologies.
The acquisition of medical imaging is usually
carried out by the radiographer or radiologic
technologist. The radiologist then interprets or
"reads" the images and produces a report of
their findings and impression or diagnosis. This
report is then transmitted to the ordering
physician, either routinely or emergently.
Initially, radiology was the science of 'Xrays', but today it involves a variety of
imaging techniques to study and
investigate patients so that a diagnosis can
be achieved.
•
• In addition, therapeutic procedures are
performed by radiologists under image
guidance, a branch also known as
interventional radiology.
What are the Different Imaging Modalities

Radiography “plain films”
Computed axial tomography “CT”
(Positron Imaging Tomography “PET”, Single Photon
Emission CT “SPECT”, Combined PET-CT)
 Magnetic resonance imaging “MRI”


Ultrasound “US”

Interventional radiology “angio”
How to Approach Reading any Image

Identify the patient

When was the image taken

Are these the proper images

The five densities

Are the images technically adequate
Radiography – X - Ray

Also called “plain films” or “standard films”

Image formed using broad beam ionizing radiation

The image formed is related to the subjects density

May involve the use of contrast agents
 Iodinated
 Barium
 Air
X-RAY 
High Energy Photon
--Kilo Electron Volts
 Ionizing Radiation
 Exposes Film /
Detector
 Projection Data
X-rays are short-wave electromagnetic radiation produced by
accelerating electrons across an evacuated tube onto a tungsten anode
using a high voltage.
• An X-ray tube is similar to a light bulb with a
filament and a current to heat the filament.
• There is also a high voltage to accelerate the
electrons from the filament at a target.
• This collision releases the x-ray radiation that is
used to image the patient.
X-RAYS PLAIN FILM
RADIOGRAPHY - Clinical uses






Chest
Bones
Spine / Extremities / Skull
Soft tissue
Mammography / Abdomen
These are the 5 typical body regions that the plain x-ray
is used to evaluate.
X - RAY --- FIVE BASIC DENSITIES
 Air / Gas
 Soft Tissue / Fluid
filled space
 Bone
 Fat
 Metal
• The x-rays can traverse tissue to create the image.
• We can only separate the 5 basic densities noted.
Air / Gas, Soft tissue / Fluid filled space, Bone, Fat
& Metal.
• Here we see the Air in the lungs, the soft tissue of
the heart and the bone density of the ribs.
• Water will appear of the same density as soft
tissue and cannot be separated. Fat is difficult to
see on the chest and better noted on abdominal xrays
CONTRAST RADIOGRAPHY

Injection, ingestion, or other placement of opaque material
within the body.

Improves visualization and tissue separation.

Can demonstrate functional anatomy and pathology.
Contrast agent: dense fluids containing elements of high
atomic number
• Administering a contrast agent modifies the image to
give more information.
Clinical uses :• Typical ones are barium, an inert particulate contrast
used in GI tract evaluation.
• Iodine, a water soluble agent which can be injected
into the vascular tree.(ANGIOGRAPHY) + intravenous
agents to visualize the renal tract (intravenous
pyelogram - IVP)
• Interventional procedures
UPPER GI--(GASTRO INTESTINAL)
ORAL BARIUM CONTRAST
ARTERIOGRAM
INTRAARTERIAL IODINE CONTRAST
• The contrast agent -Barium- will outline the GI
tract, determine size and show patency or
obstruction.
• The contrast agent-Iodine can be injected and is
water soluble.
• In the blood stream, it will outline the vessel and
demonstrate anatomy.
• Iodine is also filtered by the kidney and can show
information about tissue function
Computed Axial Tomography
Computed Tomography (CT scan): medical imaging procedure
that utilizes computer-processed X-rays to produce
tomographic images or 'slices' of specific areas of the body.
It Involves ionizing radiation.
The X-ray tube is rotated around the patient and X-rays pass through
them and are detected by photomultiplier tubes at the opposite end
of the beam.
Different tissues absorb or 'attenuate' the X-ray beam by different
amounts.
A computer processes the information about the attenuation in each
picture element (pixel) into an axial image of the area being examined.
In conventional CT the images are acquired a slice at a time with a slice
thickness varying from 2 to 10 mm.
In helical (spiral) CT the image is acquired volumetrically in a
continuous movement with no gaps between the slices imaged. This
enables the images to be manipulated in different planes and also
allows structures to be viewed in three dimensions.
Uses - CT
• Oncology staging
• Trauma assessment
• Guiding biopsies
• Radiotherapy planning
COMPUTED TOMOGRAPHY
CT

HIGH ENERGY PHOTON

IONIZING RADIATION

EXPOSES DETECTOR

TOMOGRAPHIC DATA
• In CT scanning, we are able to get slice images or
tomographic.
• TOMO=Slice, then Tomography=Slice Imaging
• Detectors in the CT scanner count the x-ray
photons that traverse the patient from a rotating
x-ray tube and use this data to assign a numerical
value (CT number) to the tissue within the patient.
• The computer then assigns a whiteness or
blackness to the tissue based on its CT number
Here the yellow line is showing the level where the CT section is made through
the upper abdomen at the level of the liver.
LT
Interventional Radiology
Interventional radiology (IR or VIR): a medical subspecialty of radiology which utilizes minimally-invasive
image-guided procedures to diagnose and treat
diseases.
Also called angiography or “angio” or “IR”
 Image formed using broad beam ionizing radiation
(fluoroscopy)
 Usually involves the use of iodinated contrast agents
and long catheters
 Many varied techniques including the use of CT or
MRI

Nuclear Medicine
Nuclear medicine: a medical specialty involving the application of
radioactive substances in the diagnosis and treatment of disease.
The radioisotopes produce gamma-rays that are emitted by the
patient following intravenous injection of the isotope.
The rays are detected by a gamma camera.
Radioisotope investigation allows the assessment of function as well
as structure.
The commonest radioisotope used is technetium, which has a half-life
of 6 h. Radioisotopes can be tagged with other substances that are
selectively taken up by the parts of the body which are being
examined.
Common radioisotope investigations
1- Bone scan - Tc phosphonate to look for
metastases
2- Lung ventilation - Tc DTPA aerosol,
krypton gas
3- Lung perfusion - Tc micro-aggregate
albumin to assess perfusion
4ventilation/perfusion
scans
for
investigation of pulmonary emboli
5- Cardiovascular - thallium scanning to look for
cardiac perfusion abnormalities
6- Renal tract - DMSA, DTPA, MAG 3 for assessing
renal structure (DMSA) and function (DTPA and MAG
3)
7- Thyroid - iodine or technetium to assess thyroid
function/nodules
Ultrasound
Ultrasound: an oscillating sound pressure wave with a
frequency greater than the upper limit of the human
hearing range.
Also called “sono” or “echo” or “US”
 Image formed by transmitting and receiving high
frequency sound waves
 Image “slices” reconstructed by computation
 The image formed is related to interfaces between
tissue areas of differing sound transmission
characteristics
 Image display on computer or multiple films

Ultrasound does not involve ionizing radiation.
It uses the principle of high-frequency sound waves, which
when reflected back from structures in the body can be
converted into a grey-scale image.
Ultrasound is a real-time examination, which means that a
moving image of the body is seen on a screen, as are the
scans.
Doppler ultrasound is used to measure blood flow in
vascular structures and depends on the principle that there
is a shift in reflected sound frequency from flowing blood in
vessels.
Advantages
• Non-ionizing (no radiation)
• Safe
• Can be used to follow up
patients
• Images in real-time –
instantaneous
• Can be performed at the
bedside
• Relatively cheap
Disadvantages
• Difficult in obese patients
• Views are often obscured by
air/bowel gas
BASIC ULTRASOUND PHYSICS
Acoustic Windows
Dense & elastic structures
Liver
Spleen
Fluid-filled structures
Heart
Urinary bladder
Typically the ultrasound probe is placed over areas that transmit the sound best for
imaging. These regions are called acoustic windows.
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ULTRASOUND
ideal for fluid filled structures
Gallbladder
Kidney
Obstetrics
Magnetic Resonance Imaging
Magnetic resonance imaging (MRI): a medical imaging
technique that uses a magnetic field to visualize
internal structures of the body in detail.
 Also called “MRI” (used to be NMRI)
 Image formed by transmitting and receiving radio
waves inside a high magnetic field
 Image “slices” reconstructed by computation
 The image formed is related to:
 Scanner settings
 Patient hydrogen density
 Patient hydrogen chemical/physical environment

Image display on computer or multiple films
MRI: an imaging modality involves the use of radio-waves and
magnetic fields to create an image of the body.
It does not involve ionizing radiation.
The patient is placed in a magnet and a radio-wave applied.
The nuclei of hydrogen atoms in water and fat absorb these waves and
emit radiofrequency energy and this can be manipulated by computer
to produce an image.
Imaging can be conducted in several planes, e.g. coronal, sagittal and
axial.
Imaging depends on the fact that pathological tissues return a
different signal to normal tissue and this property is utilized in trying
to make a diagnosis from the images.
USES - MRI
•
•
•
•
•
•
Brain, especially pituitary, posterior fossa
Spinal cord
Musculoskeletal
Abdomen/pelvis
gynecological malignancy
liver
Contra-indications – MRI
(Limitations within the MRI room)
• Pacemakers
• Metallic foreign bodies etc
• Claustrophobia
MAGNETIC RESONANCE

Hydrogen protons in a
magnetic field

Radio wave signal
transmission

No ionizing radiation

Tomographic data
With magnetic resonance, the tissue response to magnetic fields and radio waves serves as the
basis for imaging. The images are slices or tomographic and the plane of section can be
determined by the machine.
Anterior
MAGNETIC
RESONANCE
R
T
EXAMPLES
 Brain
 Spine
Anterior
Posterior
Posterior
 Knee
Anterior
Posterior
Ionizing Radiation

Radiation causes ionization of atoms and
molecules.

Ionization is the underlying mechanism for most
radiation detectors and also is responsible for
most radiobiological effects.
Biological Effect of Radiation

Why should we protect ourselves from radiation?
Direct molecular absorption of
energy
DNA most susceptible
Indirect Action-Radiolysis of Water
Ionization
Dissociation
Free Radical Biological Damage
 Cause damage to
(DNA/RNA) which
become nonfunctional
Somatic Effects

Acute or early (deterministic)





within days
dose dependent
Seen in accidents and nuclear wars
Affects acutely bone marrow, GI tract and skin
and less neurological system.
Latent or delayed (stochastic).
 not seen for years
 cancer, cataract, shortened life span
Principals of Radiation Protection
 Time
 Distance
 Shielding
 ALARA (As Low As Reasonably
Achievable)
TIME
•
•
The total radiation exposure to an
individual is directly proportional to the
time he is exposed to the source.
Therefore, it is wise to spend no more
time than necessary near the source of
radiation.
DISTANCE
•
The intensity of radiation from a source
varies inversely with the square of the
distance.
•
Therefore, radiation workers should
maximize the distance between
themselves and the radiation source.
Shielding
•
Lead is most commonly used to shield photons in
diagnostic imaging.
Angiography
Angiography: a medical imaging technique used to
visualize the inside of blood vessels and organs of
the body, with particular interest in the arteries,
veins and the heart chambers.
 Real time X-ray study
 Catheter placed through femoral artery is directed
up aorta into the cerebral vessels.
 Radio-opaque dye is injected and vessels are
visualized
 Gold standard for studying cerebral vessels.
Angiography
AP Right ICA
Lateral Right ICA
AP Right Vertebral