15. Medical Imaging Flashcards
What are the 3 planes?
Sagittarius plane
Coronal plane
Transverse plane
What is the Sagitta plane?
anatomical plane which divides the body into right and left parts.
What is the coronal plane
vertical plane that divides the body into ventral and dorsal (belly and back) sections
What is the transverse pane?
an imaginary plane that divides the body into superior and inferior parts. It is perpendicular to the coronal plane and sagittal plane.
What are the different types of direction?
- Proximal - distal
- Lateral - medial
- Superior - inferior
- Anterior - posterior
What does proximal and distal mean?
Proximal - nearer towards body
Distal - further away from body
What does lateral and medial mean?
Medial- towards the midline
Lateral - away from the midline
What does superior and inferior mean?
Superior - top
Inferior - bottom
What does anterior and posterior mean?
Anterior - front
Posterior - back
What are the two types of plain film imaging?
X-Rays
Fluoroscopy
What is x-ray?
An electromagnetic wave
How do x-rays give an image ?
- Focused beam of high energy electrons
- These can pass through the body onto receiver
- But some are absorbed or scattered (attenuation)
What does attenuation depend on?
Depends upon density and atomic number (metals)
What does more dense or higher atomic number mean?
More Dense/Higher Atomic Number = More Attenuation = Lighter Appearance
What is the most dense tissue n the body?
Bone
What no longer acts as receivers of x-ray images?
Cassettes -create electrical signal when exposed to X-rays
Where are the x-rays electronically stored?
In PACS (picture archiving and communications systems)
What are the advantages of using cassettes and PAC rather than films?
◦ Zoom
◦ Alteration of Density
◦ Measurement of Distances
◦ Measurement of Angles
How do you read an x-ray?
Systematic Approach:
- Date Taken
- Patient Demographics
- Penetration
- View (PA/AP/lateral)
- Rotation
What mnemonic is used to read a cast x-ray?
ABCDE
What mnemonic is used to read an abdominal X-ray?
ABDO
What are the advantage of using X-rays?
Quick
Portable
Cheap
Simple
What are the disadvantages of X-rays?
- Radiation (but relatively low)
- One plane so two dimensional
- Would not see all pathology
- Can’t visualise all areas
- Poor soft tissue imaging
Describe fluoroscopy
> Examination of anatomy and motion
Uses constant stream of X-rays
Often enhanced by contrast
What is contrast?
Contrast – Barium, iodine or gadolinium (MRI)
◦ Strongly Absorb X-Rays – Dense White
◦ Any space it can be swallow, inserted or injected
What are the uses of fluoroscopy?
>Angiography >Contrast GI Studies >Therapeutic Joint >Injections >Arthrograms >Screening in Theatre
What are the advantages of fluoroscopy?
> Dynamic
>Studies Cheap >Interventional Procedures
What are the disadvantages of fluoroscopy?
> Clinician Exposure Must Be Minimised
>Radiation
What are the two types of cross-sectional imaging?
> CT
>MRI
Describe what happens in computed tomography?
Rotating Gantry ◦ X-Ray Tube on One Side ◦ Detectors on the Other Images put together by computer Same Principle of Attenuation as X-rays
What does a negative Hounsfield Units (HU) indicate?
Less Dense = Negative
What does a positive Hounsfield Units (HU) indicate?
More Dense = Positive
What are the advantages of CT scans?
> Quick
>Good spatial resolution >Can scan most areas (but not all)
What are the disadvantages of CT scans?
>Radiation >Lower contrast resolution >Affected by artefact >Requires breath holding (not all patients may manage) >Overuse (‘fishing for diagnosis’) >Incidental findings
What are CT scans used for?
> Diagnosis – Cancer, stroke, bony injury, blood flow
> Guide Further Tests or Treatment – Radiotherapy, biopsy
> Monitor Conditions – Cancer treatment
How does MRI scans work?
- Strong, magnetic field 2. Aligns hydrogen atoms 3. Some point towards head and some towards feet
◦ But not 50/50
◦ Unmatched ions remain - Radiofrequency pulse applied
- Unmatched ions absorb energy and spin in different direction
- Pulse is turned off and atoms spin returns which emits energy
- Computer processing to generate image
What is MRI Weighting?
Different ‘relaxations’ produce different weightings from tissues
What is the colour of fat and water in T1 weighting?
Fat is white, water is black
What is the colour of fat and water in T2 weighting?
Water is white, fat is black
In MRI scans, is white high or low signals?
White = High Signal
In MRI scans, is black high or low signals?
Black = Low Signal
What are MRI scans used to look at?
> CNS – Brain and spinal cord
Bones and Joint
Heart and Blood Vessels
Internal Organs
What are the advantages of MRI scans?
> No Radiation
> Good contrast resolution
What are the disadvantages of MRI sans?
> Expensive > Time Consuming > Availability > Claustrophobic > Some Patients Wont Fit > Loud > Need to Lie Still > Metalwork (although lots now MRI safe)
Describe Scintigraphy (Nuclear Medicine)
> Injection of radiopharmaceuticals
they Emit gamma rays which are detected to show where they are emitted from
Highly sensitive
provide Functional and anatomical information
What are X-ray used for?
- Chest – Infection, pneumothorax, trauma, effusion, oedema
- Bowel – Dilatation, perforation
- Orthopaedic – Is there a fracture, trauma
- Post-Procedure – Nasogastric Tube, Pacemaker, PICC
- Dentist
