LECTURE – 1 – RHPT – 485
READING IN MEDICAL IMAGING
LEVEL - 8
X-RAY
INTRODUCTION

Discovered and named by
Dr. W. C. Röentgen at
University of Würzburg, 1895

Awarded first Nobel prize for
physics, 1901
• In 1895 Wilhelm Conrad Roentgen discovered X-rays, so
paving the way for the development of a new branch of
medicine called radiology.
• Initially, radiology was the science of 'X-rays', 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.
FIRST X-RAY
Roentgen’s wife's hand
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”
RADIOLOGY TOOLS
X- RAY
ULTRASOUND
NUCLEAR MEDICINE
MAGNETIC RESONANCE
COMPUTED TOMOGRAPHY
6
HOW IS IMAGING DONE?

IONIZING RADIATION
X-ray, CT, Nuclear Medicine

SOUND WAVES
Ultrasound

MAGNETIC FIELDS / RADIO WAVES
Magnetic Resonance
To image the patient a energy source is directed into a
volume of tissue and an image is created of the tissue
interaction.
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
X-ray beam
 Exposes Film /
Detector
 Projection Data
detector
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 typical body regions that 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.
• 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

Also called CAT scanning or “CT”

Image formed using a rotating thin beam(s) of ionizing
radiation

Image “slices” reconstructed by computation

The image formed is related to the subjects density

Image display on computer or multiple films

New technology is multislice helical scanner
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.
• 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







Also called angiography or “angio” or “IR”
Image formed using broad beam ionizing radiation
(fluoroscopy)
Images acquired using digital detector and
processed by computer
The image formed is related to the subjects density
Usually involves the use of iodinated contrast agents
and long catheters
Many varied techniques including the use of CT or
MRI
Image display on computer or multiple films
NUCLEAR MEDICINE

High Energy Photon

Ionizing Radiation
--Radiopharmaceutical

Exposes Detector

Projection Data

Dynamic / Physiologic
Here we have an example of a nuclear
medicine bone scan with anterior and
posterior views.
This branch of radiology uses radioisotopes for imaging.
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.
First test
Common radioisotope investigations
• Bone scan - Tc phosphonate to look for metastases
• Lung ventilation - Tc DTPA aerosol, krypton gas
• Lung perfusion - Tc micro-aggregate albumin to assess
perfusion
• ventilation/perfusion scans for investigation of pulmonary
emboli
• Cardiovascular - thallium scanning to look for cardiac
perfusion abnormalities
• Renal tract - DMSA, DTPA, MAG 3 for assessing renal
structure (DMSA) and function (DTPA and MAG 3)
• Thyroid - iodine or technetium to assess thyroid
function/nodules
• With Nuclear Medicine a radioactive drug is
administered, a pharmaceutical portion of the
drug has been created to localize to a type of
tissue.
• The radioactive tag of the pharmaceutical serves
to identify the site of accumulation.
• The detector or gamma camera which is similar to
a Geiger Counter measures devices that detect
radioactivity the radiation distribution and maps it
to a region.
NUCLEAR MEDICINE
 Bone
EXAMPLES
 PET scan

Liver
• Here the radiopharmaceutical collects in a specific
tissue and the radioactivity allows an image from
the count of radiation (activity).
• This can be followed over time to see functional
physiology.
• The PET scan is a scan showing increase in
metabolism measured by injecting with a
radioactive glucose… . The arrows indicate the lung
cancer on the chest x-ray and the pet scan.
Ultrasound

Also called “sono” or “echo” or “U/S”

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
• Poor Grey-scale image
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.
35
B Mode-brightness
Most common use
Presents “real time” image

Ultrasound Sector Scanning
The B mode shows intensity of reflection of the image by greater brightness. This is called
echogenicity and can be used to separate tissue.
The image shows a live screen view as a video feed would show.
ULTRASOUND
ideal for fluid filled structures
Gallbladder
Kidney
Obstetrics
Magnetic Resonance Imaging
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 is one of the newer imaging modalities that does not involve
ionizing radiation.
It involves the use of radio-waves and magnetic fields to create an
image of the body.
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
• 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
HOSPITAL TERMS
Abbreviations used frequently in the
medical community.
X- Ray
Plain Film
Scout Film
Computed Tomography
Nuclear Medicine
Ultrasound
Sono
Magnetic Resonance
Radiograph
Cat Scan
Nuc Med
Sonogram
MR
MRI
CT
X-Ray

X-ray is emitted from outside the nucleus (electron
shells).
X-rays and
gamma
rays
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
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