S1L2 - MSK Radiology Flashcards
How are x-ray images generated?
By projecting a beam of electrons through an object onto an image detector plate
What objects appear white in an x-ray?
Objects that are dense and thick and therefore absorb a lot of the radiation passing through. Often used to image bone.
What is the detector plate?
The plate that measures the radio waves not absorbed by the object. Similar to a photographic film, turning black when x-rays hit the plate.
What are the advantages of x-rays?
- Quick
- readily available
- inexpensive
What are the disadvantages of x-rays?
- involve transmission of radiation to patient (less than CT)
- poor soft tissue contrast resolution
What are x-rays commonly used for?
- skeletal trauma (fractures/joint dislocation)
- evaluation of chronic bone or joint pathologies (osteomyelitis/chronic arthritis)
What is a bone fracture?
Complete or incomplete break in the continuity of a bone.
Name the 6 different fracture types
Transverse Linear Greenstick Spiral Oblique Comminuted Epiphyseal separation
How do epiphyseal plates present on an x-ray?
Less mineralised and therefore less radio opaque so can be seen on an x-ray as dark lines. These lines generated by the epiphyseal growth plate become thinner, eventually disappearing and becoming closed.
How do we conduct a bone age study of a child?
By performing an x-ray of the child’s left wrist and comparing the degree of ossification of the carpal bones to images of those in a standard atlas of bone development.
What clinical significance does a difference between a child’s bone age and their chronological age represent?
- precocious or delayed puberty
- growth hormone deficiency
- hypothyroidism
- Hyperthyroidism
- malnutrition
What are the stages of fracture healing?
- Haematoma formation
- Tissue death
- Inflammation / cellular proliferation
- angiogenesis / formation of granulation tissue / procallus
- Soft (fibrocartilaginous) callus formation
- Consolidation / hard callus formation
- Lamellar bone
- Remodelling
What is radiographic union?
When the fracture line on an x-ray becomes completely obscured following the bone repair and remodelling
How does a CT scan work?
A CT (computed tomography) scan, also known as computerised axial tomography (CAT) scan, uses narrow x-ray beams to produce cross-sectional slices of an object which are then digitally reassembled to generate two and three dimensional images.
What are the advantages of CT scans?
- soft tissue detail is better than plain x-rays
- gives detailed information about the bone structure and pathology
- whole body CT scan can be performed in a short period of time (quicker than MRI/longer than x-ray)
- better visualisation of subtle undisplaced fractures than x-ray.
- complex fractures can be seen in greater detail
- ## slices can be reformatted to create multiplanar and 3D images.
What is the function of CT?
- used to guide injections, biopsies and aspirations in real time
What are the disadvantages of CT scans?
- high radiation dose than plain x-ray
- motion artefact if patient moves
- poor soft tissue detail when compared to MRI
- severely obese patients cannot always be accommodated within the scanner.
- some patients may be allergic to the intravenous contrast used.
How is the density of body tissues measured in a CT scan?
Hounds field units (HU)
How do we interpret CT scans?
Similar to x-rays. Sir is black, dense materials such as bone is white.
What is meant by the windows of a CT scan?
The software attached to the CT scanner can be used to manipulate the grey scale component of the image, creating different windows. This gives us the ability to focus on certain tissues of interest.
How does an MRI work?
Magnetic Resonance Imaging (MRI) utilises magnetic resonance of hydrogen nuclei to produce high quality cross-sectional images of the body in any plane. The radio frequency signal pulses are applied to the tissue which deflects the protons. When the pulse is terminated, the protons realign and emit a signal as they do so.
When is MRI used?
- good for soft tissue imaging
- detecting pathology (osteomyelitis/malignancy/muscle contusions/ prolapsed intervertebral discs/occult fractures)
- used to image tendons and ligaments.
Advantages of MRI imaging?
- better at imaging soft tissue
- useful for generating multiplanar images (images taken from multiple angles)
- patient receives no radiation
- useful for assessment of bones, joints and associated soft tissue
- excellent for bone marrow imaging
- detailed anatomy of joints.
How do we interpret T1 weighted MRI images?
Fat appears bright, fluid appears dark
