Midterm Review Slides Flashcards
What are the 3 anatomical planes?
- coronal/frontal (front and back)
- axial/transverse/horizontal (top and bottom)
- sagittal/longitudinal (left and right) – median (midline) or parasagittal (more left or right)
CT/MRI Axial View in Images – Positions
- left: right side of patient’s body
- right: left side of patient’s body
- top: anterior side of patient’s body
- bottom: posterior side of patient’s body
How does CT work?
- 3D representation
- cross-sectional image info based on tissue density, atomic weight of the molecules
- uses ionizing radiation from a source to produce an image
- source (emits radiation) and detector (picks up signal) rotate 360º around the patient as patient is moved through the scanner
- x-rays from different angles are processed by computers to create tomographic images
CT
What are the 5 major tissue densities found on radiographs, from low to high density?
air (black) < fat (dark grey) < water/soft tissue/fluid (light grey) < bone (nearly white) < metal (white)
CT
Describe the radiographic density of air.
low density
- air does not attenuate (block/scatter) the signal very well – ionizing radiation passes through the patient and hits the detector
- appears black
CT
Describe the radiographic density of metal.
high density
- metal attenuates (blocks/scatters) most or all of the signal
- appears white
CT
How does tissue density affect how it appears on radiographs?
- more dense substance → more signal attenuation (blocking) → substance appears more white
- thick structures attenuate more radiation than thin structures of the same composition
CT
What appears as white on radiographs?
bone, blood, bullets (BBB)
How does MRI work?
- 3D information
- provides images in any plane
- protons in a strong magnetic field are bombarded with low energy (non-ionizing) radiowaves
- powerful magnetic field aligns protons in the body
- when the field is turned off, protons relax and emit electromagnetic signals that are detected by the scanner (with specific amplitude and frequency), and these signals can be reconstructed in digital images of the human body
What are the main uses of ultrasound imaging? (3)
- first-line in HEART IMAGING
- evaluation of ABDOMINAL and PELVIC ORGANS – fluid-containing things and stones (bile ducts, gall bladder, renal/ovarian/breast cysts, hydroneophrosis (enlarged kidney), evaluation of stones (gall stones, renal calculi))
- determination of CYSTIC (fluid-filled) vs. SOLID STRUCTURES
How can you determine if a structure is cystic (fluid-filled) or solid in ultrasound imaging?
cysts do not reflect sound and are anechoic – appear black
What is nuclear medicine?
branch of radiology that uses intravenous radio-pharmaceuticals for imaging
- radio-pharmaceuticals may be deposited in certain tissues, and emit gamma rays
- rays are detected by gamma cameras
How does positron emission tomography (PET) work?
uses radioisotope fluorine-18 (positron emitter) to produce photons that can be imaged
- fluorine-18 can be incorporated into biologically active molecules (ie. fluoro-18-deoxyglucose used for cancer staging)
- ie. fluorine-18 labeled with glucose-like molecule – parts of the body that use glucose faster (like fast-growing cancers) preferentially take the radioisotope up
Breast Cancer
What is the screening recommendation?
every 2-3 years for every woman aged 50-74
Breast Cancer
What modality is used for screening?
mammogram (x-ray)
Breast Cancer
Describe the epidemiology (Canada).
- 2nd most common cause of cancer death in women – accounts for 15% of all cancer deaths
- accounts for 25% of all new cancer cases in women
- around 1 in 8 women will develop breast cancer in their lifetime
- can occur in males – but less common
- 5-year net survival rate is high (89%)
Breast Cancer
What is the sensitivity of the screening?
variable based on age
- detects ~73% of cancers in early 40s
- detects ~85% of cancers in early 60s
Lung Cancer
What is the screening recommendation?
annual screening up to 3 consecutive times for:
- high risk adults 55-74 years old + ≥ 30 pack-years of smoking, and currently smokes or quit within the last 15 years
- ≥ 50 years old + ≥ 20 pack-years of smoking with other risk factors
Lung Cancer
What modality is used for screening?
low dose CT (LDCT)
Lung Cancer
Describe the epidemiology.
- accounts for 13% of all new cancer cases
- 5-year net survival rate is low (22%)
Colon Cancer
What is the screening recommendation?
one of the following:
- every 1 year via fecal testing
- every 10 years via colonoscopy
- every 5 years via colonography
Colon Cancer
Describe the epidemiology.
- accounts for 10% of all new cancer cases
- 5-year net survival rate is about average (67%)
Colon Cancer
What is the sensitivity of the screening?
variable between ~86% (colonoscopy) to 96% (feces)
Heart Screening
What is a heart attack?
occurs when part of the heart muscle does not get enough blood
- most are caused by CAD (blockage of the arteries that provide blood supply to the heart)
Heart Screening
What imaging modality is used? What does it detect?
CT scan of the heart
- detects calcium deposits in heart arteries (appear as bright white areas) – build-up of calcium and fat can result in narrowing and eventually blockage of these arteries, leading to symptoms of CAD
Heart Screening
What is coronary artery calcium score (CACS)?
CT scan of the heart gives a score based on the total area of the calcium deposits and density of the calcium present
Heart Screening
A CT scan of the heart is typically performed on what population?
people who are at risk of developing CAD – ie. individuals with a family history of heart attacks
How does imaging play a role in cancer treatment? Which modality is used?
- in a newly diagnosed cancer, one crucial aspect is determining whether the cancer has spread to other parts of the body
- PET allows doctors to visualize ‘hot spots’ which can represent cancer cells
Describe how x-rays and CT scans work similarly.
- generate x-ray photons using current applied to a metal (tungsten)
- photons are directed and interact with tissues, and are received by a detector opposite the patient
What does the frontal lobe control?
- motor control (precentral gyrus)
- eye movements (lateral cortex)
- language production (Broca’s area)
- executive function (prefrontal cortex)
- reasoning and rationale
What does the parietal lobe control?
- sensory interpretation (postcentral gyrus)
- visuo-spatial processing (attribution)
- language interpretation
- attention
How do we demarcate the frontal and parietal lobes of the brain?
separated by the central sulcus
- sulcus: cleft/invagination/fold
- gyrus: ridge/elevation
Describe the motor control pathway.
precentral gyrus (grey matter) → internal capsule (white matter) → midbrain (cerebral peduncles) → spinal cord (‘cortico-spinal tracts’)
- top-down control – with the exception of reflex arcs
What is fine motor control? Where does it require input from?
nuanced motions, balance, eye reflexes, etc.
- cerebellum: balance, voluntary moves, posture
- semicircular canals (temporal bone): balance
- caudate and lentiform nuclei: tuned movements
Describe the sensation pathway.
spine → midbrain → thalamus → parietal lobe (postcentral gyrus)
- bottom-up control
- differences in control between touch, pressure, temperature, and proprioception/vibrations
What is the spinal cord?
aggregation of nerves carrying sensory and motor functions
What are the segments of the spinal cord?
- cervical: C1-C7
- thoracic: T1-T12
- lumbar: L1-L5
- sacral: S1-S5
What is nuclear medicine/PET often used for?
usually used for scanning the whole body for hot spots
What are some image-guided interventions for uterine fibroids?
- uterine artery embolization via fluoroscopy (real-time x-ray)
What is the pre-central gyrus?
part of frontal lobe responsible for motor control (voluntary movement)
What is the post-central gyrus?
part of the parietal lobe responsible for sensory interpretation
What separates the pre-central gyrus and the post-central gyrus?
central sulcus
How do CT images compare to MRI images?
fuzzy, grainy, bright (especially outlines)
What is bile?
- mixture of water (> 97%) and salts, cholesterol, fatty acids
- produced by the liver
What are the functions of bile?
- surfactant – reduce surface tension in tracts and the digestive system
- emulsification – forms rounded ‘micelles’ around fat globules
result: along with pancreas enzymes (lipase), bile breaks down fatty acids and allows absorption by villi (small bowel)
What are the two radiographic views?
- posteroanterior (PA): x-ray beam enters from behind
- anteroposterior (AP): x-ray beam enters from front
Which radiographic view is less frequently used?
anteroposterior (AP)
Which radiographic view are radiographs in the supine (laying down) position done in?
normally anteroposterior (AP)
- indicated on radiograph with ↓
- magnifies cardiac/mediastinal shadow by 20-25%
What is the CT (cardiothoracic) ratio?
(maximum transverse diameter of heart) / (maximum transverse diameter of rib cage)
What CT ratios are suggestive of cardiomegaly?
- CT ratio > 0.5 on PA view
- CT ratio > 0.6 on AP view
Why might structures look bigger or smaller in radiographs?
- depends on radiographic view
- the further the structure from the radiographic plate, the larger they appear on film
How many ribs do humans have?
12 on each side
- ribs 1-10 are connected to the sternum by costal cartilage
- ribs 11-12 are floating
Describe how ribs appear on posteroanterior (PA) film.
- posterior ribs are more apparent on PA film, up to 10 visible on full inspiration – recall the further the structure is from the radiographic plate, the larger they appear on film
- anterior ribs are less visible on PA film
Describe the different settings on CT.
window level – midpoint of grayscale range
- decrease WL: increase brightness
- increase WL: decrease brightness
What is MRI imaging excellent for?
- soft tissue imaging, staging of lung/soft tissue neoplasm
- cardiac imaging
What is MRI imaging limited in?
- aerated lung imaging
- bone imaging
(skeletal or air)
What are the disadvantages of MRI?
- expensive
- longer examination time
What is ultrasound imaging good for?
- ‘first line’ in heart imaging
- localizes pleural effusions
- characterizes superficial soft tissue lesions on chest wall
What are the advantages of ultrasound?
- more readily available
- portable
- inexpensive (less than CT or MRI)
- few contraindications for use
- real-time imaging
- doppler evaluation of organs and vessels
- not adversely affected by metallic objects
- can easily be extended to cover any organ