Imaging Modalities Flashcards
Why is William Rontgen important?
Discovered Xray radiation
Why is John Halls-Edwards important?
First medical use of Xrays
What type of radiation is in Xrays?
Electromagnetic
What is the wavelength of X rays?
0.01-10 nm
What are the biological properties permitting Xray imaging?
Different tissues absorbs Xrays at different rates.
Cause excitation of atoms
What is different between excited vs non-excited atoms?
Excited atoms enter reactions not available to non-excited atoms
What can long term exposure to or high dosages of x rays lead to?
Somatic or genetic changes.
What does more absorption in X rays result in?
White on image
What type of tissue appears white?
High density tissue
Give an example of high density tissue
Bone
How does low absorption appear on x ray?
Black
What does black on an x ray indicate?
Low density tissue
Give examples of low density tissue
Lungs, air spaces
How does intermediate absorption appear on X ray?
Shades of grey
What type of tissue has intermediate absorption/appear grey on x ray?
Intermediate density tissue
Give examples of intermediate density tissue.
Muscles, some connective tissue (e.g. adipose)
What is important to remember when interpreting an x ray?
2D image of 3D space
What tools can be used to help interpret an x ray?
Superimposition
Several angles
Colour differences
What type of structures can be seen in an x ray?
Normal or abnormal
Calcifications
Tumours/neoplasias
Infections (e.g., pneumonia)
Foreign objects
What can absences of structures in x rays indicate?
Air spaces
Pneumo-/hemo-thorax
Fractures
When were CT scans developed?
1967
Who developed CT scans?
Sir Godfrey Houndsfield
When was the first medical use of a CT scan?
1971
What are CT scans used for?
Non-invasive imaging and diagnosis
What can CT scans help us do?
3D reconstruction of injuries
3D printing of structures for surgical planning
How do CT scans work?
X rays from multiple orientations
Computer sums or stacks a complete image
What are the biological properties of CT scans?
Same as Xray but at higher doses
What are different types of CT scans?
Sequential CT
Spiral CT
Electron beam tomography
Dual energy CT
CT perfusion imaging
With or without contrast
What is attenuation?
X rays transmitted - x rays absorbed by body
Differentiate between high and low density tissue in CT scans.
High - absorbs more radiation and less detected by scanner; brighter/white
Low: absorbs less radiation and greater signal detected by the scanner; grey to black
What is the orientation of a CT scan?
Looking superiorly/cranially
What does RALP mean in CT scans?
Right, anterior, left, posterior
What structures can be seen in a CT scan
Normal or abnormal
Calcifications
Tumours/neoplasias
INfections
Foreign objects
bleeding
What can structure absences indicate in CT scans?
Air spaces
Fractures
Pneumo-/hemo-thorax
Who invented MRI scans?
I. I. Rabi
When were MRI scans invented?
1930s
When did MRIs become common for soft tissue investigations?
1980s
When did MRIs begin to be used in medical settings?
1970s
Describe how MRI scans work
Images H2O containing tissues
Hydrogen protons have magnetic poles
Without a magnetic field poles align randomly
Turn on magnet - poles line up
Send a radio transmission to disrupt poles
Disruption causes pole switch
Turn off RT and pulse re-emitted
Turn off magnetic - poles return to unaligned position
Different tissues have different return rates
Measuring difference = image processing and reconstruction
What are the three types of weight settings for MRIs?
T1, T2, Flair
What does weighting mean in MRI?
Images will appear with different densities with different weight settings
What differences in weights of MRIs result in the different densities?
Based on length, repetition, and strength of radio transmission pulses
What does white indicate in a T1 weighted image?
Fat
Protein rich fluid
What does white indicate in a T2 weighted image?
Water content e.g. inflammation
Tumour
Haemorrhage
Infection
What does intermediate colouring indicate in a T1 weighted image?
Gray spinal matter darker than white
What does intermediate colouring indicate?
White spinal matter darker than gray spinal matter.
What does dark colouring indicate in a T1 weighted image?
Bone
Air
Water content e.g. inflammation, tumour, hemhorrage
What does dark colouring indicate in a T2 weighted image?
Bone
Air
Fat
What are the three anatomical planes in which MRI can produce images?
Sagittal, coronal, transverse
How do you orient yourself in transverse MRI views?
RALP
Describe how CSF appears in each MRI weight.
T1: Dark
T2: Bright
Flair: Dark
Describe how white matter appears in each MRI weight.
T1: Light
T2: Dark grey
Flair: Dark grey
Describe how the cortex appears in each MRI weight?
T1: Gray
T2: Light gray
Flair: light gray
Describe how fat within bone marrow appears in each MRI weight
T1: Bright
T2: Light
Flair: Light
Describe how inflammation appears in each MRI weight?
T1: Dark
T2: Bright
Flair: Bright
What to determine when interpreting an MRI.
Body region
Orientation
Weighting
When are MRI scans used medically?
Anywhere contrast resolution is required (use tracer or dye to enhance)
Soft tissue imaging
What can be determined in MRI soft tissue imaging?
Differentiates between muscle, water, fat
Tumours versus healthy tissue
Rupture of structure
What are the two types of forensic uses of medical imaging?
Antemortem
Postmortem
What can antemortem medical imaging help with?
Detect injury
Document injury
How can medical imaging be used postmortem
Virtual autopsy
Why might a virtual autopsy be used?
Healthcare worker safety
Accommodate religious observance where possible
Can be sufficient but largely ancillary to full autopsy
What are the two types of post mortem medical imaging
PMCT - post mortem computed tomography
PMMR - post mortem magnetic resonance
How do postmortem exams work in Australia?
PMCT is the primary exam
Followed by traditional autopsy
How do postmortem exams work in Germany?
PMCT is secondary exam
At the order of the legal authority
Prosecutor
For homicides or malpractice only
How does the forensic pathology service use PMCT?
All individuals brought to the Coroner’s Facility in Toronto
Who uses PMCT in Ontario?
Forensic pathologists, radiologists (more complex cases), anthropologists, odontologists
What can PMCT be used for in forensics?
Diagnosis
Age estimation (adult and fetal)
When can PMCT be used for identification?
Where antemortem record is available
When was the first time PMCT was used in the US?
2012
What are the 4 agencies in the US that use PMCT?
NM, MD, LA county, AMFEO
What is required when PMCT is submitted into court as evidence?
Requires testimony to ensure renderings are true.
