L1. Conventional Projection Radiography Flashcards
Radiation and public risk perception of x-ray technology
Risk of using radiation for x-ray technology varies depending on various factors including whether radiation is manmade vs. natural
Examples of factors that make communication of radiation risk challenging
Radon
Medical uses
Nuclear accidents
Lifestyle factors e.g microwaves, radio, sun
The key to radiation protection
Understanding risk vs. benefit
What is an X-Ray?
Form of electro magnetic (EM) radiation
Electromagnetic radiation
Spectrum depicting different energy levels of individual photons, in relation to wavelength/frequency of photons
Examples of low frequency, non-ionising radiation
Phones
Communication wires
Radio
Microwave
Visible light
Examples of high frequency, ionising radiation
Ultraviolet
X-Ray
Gamma ray
Order of electromagnetic spectrum (low to high)
Radio
Microwave
Infrared
Visible
Ultraviolet
X-Ray
Gamma Ray
Ionising radiation
Radiation with sufficient energy to remove electrons from their shells can cause ionisation
Ionisation in human cells due to radiation exposure
DNA may be damaged directly or indirectly
Indirect ionisation
Through free radical formation e.g. ionised water -
Thought to cause most biological damage because water is much more abundant than DNA
History of X-Ray
Discovered in 1895 by German physicist & mathematician Dr. Wilhelm Conrad Roentgen who received first nobel prize for developing the first X-Ray tube
What year was X-Ray first introduced in Ireland?
1896
Characteristics of X-Ray
Invisible
Electrically neutral
No mass
Travel at speed of light in vacuum
Cannot be optically focused
Travel in straight lines
Cause some substances to fluoresce
Cause chemical changes in radiographic and photographic film
Can penetrate the human body
Can produce secondary radiation
Can cause damage to living tissue
Protons
Positive charge
Neutrons
Neutral
Electrons
Negative charge
Where do X-Rays come from?
X-rays produced when rapidly moving electrons that have been accelerated through a potential difference of order 1kV to 1mV strikes a metal target
Production of X-Rays (more detail)
Electrons from a hot filament are accelerated onto a target anode. When electrons are suddenly decelerated on impact, some of the kinetic energy is converted into EM energy as X-rays.
How much energy supplied is converted into X-radiation during this process?
Less than 1%, with the rest being converted into the internal energy of the target
Polychromatic radiation
Photons produced will have a range of energies
Voltage produced by X-ray tube
100,000V
How many volts used for finger scan?
48-50 thousand volts
X-ray interaction processes
When radiation passes through matter, it is attenuated by processes of absorption and scattering
Attenuation
Results in a reduction in the intensity of the incident radiation beam
Absorption
Results in transfer of energy from x-ray photon to atoms of the material - the photon’s energy is totally absorbed
Scattering
Involves photon deflection from original course, it only loses energy to material it is passing through
Contribution of x-rays to radiographic image formation
A beam of x-ray photons is produced using an x-ray tube
The beam is passed through a patient’s body
Some tissues will attenuate more than others
Beam of photons exiting the patient is more intense in some places than others
An image receptor (digital) reacts to x-ray photons and captures image
Areas of receptor subject to more radiation gain more signal, displayed as darker on film
Photoelectric absorption
Incident photon interacts with electron of inner shell, with incident photon completely absorbed
Compton scattering
Interaction between incident photon and an outer shell electron results in electron ejection and scattering
Main source of staff exposure
Protective shielding used to prevent exposure
Beam attenuation
The beam emitted from the patient contains the radiologically significant information needed to make a diagnosis
Factors affecting the amount and type of attenuation that happens
Atomic number of tissue
Density of tissue
Thickness of tissue
Energy of x-ray beam
Atomic number and density of air
7.78, 1.29kg/m^3
Atomic number and density of fat
6.46, 916kg/m^3
Atomic number and density of water
7.51, 1000kg/m^3
Atomic number and density of muscle
7.64, 1040kg/m^3
Atomic number and density of bone
12.31, 1650kg/m^3
The human body acts as an ______________ during x-ray
Attenuator
Air as an attenuator
Air will absorb fewer photons allowing more photons reach the image receptor creating a greater image receptor exposure
Fat as an attenuator
Soft tissue similar to muscle but lower density and atomic number
Muscle as an attenuator
Soft tissue withh higher atomic number and density to fat leading to greater attenuation of the beam
Bone as an attenuator
Calcium content and high atomic number with the greatest tissue density. Greatest absorber of photons with less reaching image receptor.
Contrast agents
Introduction of high density agents into low density regions to enhance differences between organs of body during x-ray e.g. barium, iodine, air
Darkness on an x-ray indicates
Low density regions which do not attenuate x-ray - radiolucent e.g. lungs containing gas
How can contrast agents be applied?
Orally
Rectally
Intra-venously
Intra-arterially
Fluoroscopy
Taking multiple low-dose x-ray images in succession to create a real time, stop motion video
Applications of fluoroscopy
In the surgical theatre - check fixation of devices
GIT system and blood vessel imagery (angiography)
Limitation of conventional projection radiography
2D image does not fully represent 3D structure, therefore images are taken from multiple angles
Harmful effects of ionising radiation
Pose risk to patients, staff, public and unborn children
Can often lead to radiation burn, hair loss
Tissue reactions
When radiation exceeds threshold level, tissue function compromised due to cell death beyond tissue capability
Tissue reaction side effects
Skin reddening
Cataract
Permanent sterility
Acute radiation syndrome (ARS)
Higher dose of radiation
Increases risk of cell damage and death
Severity of radiation effects
Proportional to dose received over threshold
Threshold of tissue reactions
Much higher than doses delivered during standard general radiographic examinations
Stochastic effects
Cell DNA damage can lead to mutation, replication and cancer
Effects random in nature
Somatic - occurs in individual
Genetic - occurs in offspring
Any amount of radiation carries a risk however
Smaller amount of radiation, lower risk with the probability of occurence assumed proportional to dose received
There is NO threshold….
below which zero effects can occur
Stochastic effects additional info
Cardiovascular disease risk
Increased risk of developing childhood cancer
Pillars of Risk Reduction
Justification
Optimisation
Dose limitation
Ways to optimise staff dosage
Time
Distance
Shielding/protection
Xray and pregnancy
Low dose administered to pregnant woman to reduce risk of childhood cancer
Young, undifferentiated tissue more sensitive to mutation
Greater risk of stochastic effects in youths
Justification and optimisation key for pregnant cases
PROS
Accessible
Fast
Cost effective
Short waiting lists
Minimal preparation
Minimally invasive
CONS
Limited detail on soft tissue organs
Limited detection of early diagnosis in bone disease
Non specific findings in some disease processes
2D image of 3D image structure
Anatomy only, limited functional and physiological info
Clinical applications of CP radiography
Chest
Skeletal trauma
Imaging for exclusion
Follow up
Suspected physical abuse (SPA)
Summary of CP radiography
Xrays pass through patient
Some attenuated, some pass through patient to detector
Density, atomic number and thickness can influence penetration
How do we overcome the limitation of the 2D image?
Take images from multiple angles
Assessment of skeletal trauma
Fracture/dislocation
Presence and severity
Healing or infection
Signs of fracture
Disrupted cortical outlines
Radiolucent lines
Misalignment of bony fragments etc.
Aswell as visible disruption to bony anatomy…
skeletal trauma may be associated with other signs on projection radiographs such as fluid levels, visible fat pads etc.
Fat fluid level..
where blood and fat have leaked from the fractured bone, and the less dense fat lies on top of the more dense blood
Fracture healing
Checkup assessment to monitor healing where avascular necrosis indicates insufficient healing
Degenerative changes assessed with projection radiography
Osteoarthritis (joint space lost, sclerotic bones, subchondral cyst) and rheumatoid arthritis (loss of joint spaces, ulnar deviation, soft tissue swelling and hitchhiker’s thumb)
Assessment of bone or joint pain
Tumours (osteocarcoma - bone cancer) show heterogenous, areas on new bone formation (white)
Paget’s disease
Excessive bone remodelling
Advantages of projection radiography
Readily available
Fast
No waiting lists
Cost effective
Minimal prep required by patients
Non-invasive in almost all cases
Contrast is minimally invasive
Radiation dose lower than alternative modalities
Limitations of projection radiography
Use of ionising radiation
Generates a 2D image of 3D anatomy
Limited visualisation of soft tissue structures
Can be limited in early diagnosis in bony disease e.g bony metastasis
Non-specific findings in some disease processes
Possible allergic reactions to contrast agents
Radiation dosage
More projection xrays carried out however lower dosage than CT scan
Larger denser body parts usually…
require higher doses of radiation
Chest mSv
0.02
Lumbar spine mSv
0.57
Knee mSv
0.00058
Abdomen mSv
0.4
Example of projection radiography in research
Etanercept - tumour necrosis factor used in treatment of rheumatoid arthritis
Research to improve radiography
Optimisation of patient imaging e.g. studies investigating radiation dose and image quality
Forensic studies
Widely used tool in forensic examination
Oldest form of radiographic imaging
Conventional projection radiography based on attenuation of xray photons by different tissues
