Imaging Flashcards
What are X-rays?
High energy electromagnetic radiation
How are xrays created?
Release of electrons from a superheated tungsten cathode in a vacuum drawn towards tungsten anode at high speed - collision of electrons = heat and xrays
Bremsstrahlung / Braking radiation
Which tissues absorb high proportions of xrays?
Tissues with high atomic nucleus
High beam attenuation (metal)
What are the 3 different types of receptors in X-rays?
Conventional
Digital
Fluoroscopic
Digital receptors substitute a cassette for which 2 types of radiography?
- Direct
2. Computed
What are the components of fluoroscopic receptors? 5
Input window Input phosphorus plate Photocathode Accelerating anode Output phosphor screen
Factors to decrease exposure?
- Decrease time
- Max distance from surgeon
- Xray producer further image intensifier closer (min scatter)
- Shielding
- Collimation (Reduction of window size)
What does the MRI magnetic field do to the water protons in the body?
Align and synchronise spin
What happens when a RF pulse is applied during an MRI?
Forces the protons to change alignment - tilt 90 degrees - transverse magnetization + synchronises precession
What energy is used to create the MRI image?
Relaxation of the protons - energy released
What is the spinning-top-like spin/ wobble of protons referred to in an MRI?
Precession
What is a T1 image?
Time taken for magnetisation to return to the longitudinal axis after a RF
What is a T2 image?
Time taken for protons to lose TRANSERSE magnetisation
What is a T1 image good for?
Anatomy
Which phase is gadolinium used for T1/T2?
T1
What is a STIR?
Short tau inversion recovery
What is a STIR good for?
Sensitive to abnormal fluid
Tumours and trauma
What is a T2 image good for?
Pathology
Soft tissue
How are ultrasound waves generated?
Electric current through a piezoelectric crystal
What freq are ultrasound waves generated?
3-50MHz
Units used to measure the attenuation coefficient in cT?
Hounsfield units
Xray beam producing a collimated fan shaped X-ray beam that helically rotates around the patient?
CT
How does a bone scintigraphy scan work?
Detects distribution of injected radio labelled tracer in gamma ray sensitive tissues
Indications for bone scintigraphy? 4
Tumour
Infection
Mets
Occult/stress #
Name the tracers used in bone scans?
Technitium 99 - OB
Gallium 67 - Inflamm proteins
Indium 11
What are the 3 different phases in a bone scan?
Flow phase - nuclear angiogram
Blood pool phase
Static phase - bone activity
What is a DEXA scan?
Dual energy X-ray absorbitometry
Where are the 2 regions scanned in a DEXA scan?
Lumbar spine
Proximal femur
What is a PET scan?
Positron Emission Tomography scan
What is a PET scan capable of measuring?
Body function
Glucose uptake
Blood flow
02 consumption
What are the 3 components in a PET Scan?
Cyclotron
Camera
Computer
