L18- Introduction to medical imaging Flashcards
two broad typical of medical imaging
plain filming imaging
cross sectional imaging
plain film imaging
X-ray
Fluoroscopy
cross sectional imaging
CT
MRI
x-rays are part of the
electromagnetic spectrum
X-ray is higher frequency than….. but lower than …..
UV
Gamma
how does an X-ray work
- X-ray soruce focuses a beam of high energy electrons that pass through the body onto an X-ray receiver
- Some X-rays are absorbed
- Some x-rays are scattered (attentuation)
attenuation is dependent on
the density and atomic number of tissue constituents e.g. metals like calcium in the bone
the more dense (e.g. bone)
the more attenuation (scattering) and lighter the appearance
in X-rays there are .. principle densities
5
name 5 principle densitities
air
fat
soft tissue
bone metal
X-rays used to be visualised manually on film, however now they can be visualised on
Picture Archiving and Communication Systems (PACs)
Picture Archiving and Communication Systems (PACs) advantages
Zoom
Alter density
Measure distances
Measurement of angles
fluoroscopy is a method used in
X-ray
fluorscopy can be used to
Examination of anatomy and motion
- Uses constant stream of x-rays
- Enhanced by contrast
Contrast media
Where contrast agents is used to better differentiate tissue during medical imaging.
Contrast media:
a substance used to increase the contrast of structures or fluid within the body in medical imaging. Contrast agents absorb or alter external electromagnetism or ultrasounds.
Different types based on modality of examination
(Different radiopharmaceuticals, which emit radiation themselves).
Examination techniques which use contrast media
Fluoroscopy
CT
MRI
Arteriograms (e.g. cardiogram with dyes)
Ultrasound
Two categories of contrast agentP
Positive agents- appears white (high atomic number)
- Barium
- Sulphate
- Iodine
Negative agents- appears black (gases of low density)
- Air
- Oxygen
- Carbon dioxides
Agents can be combined to produce a double-contrast
Ideal Phase Contrast Agents
- Low osmolality and viscosity
- High water solubility
- Biologically inert
- Safe
- Heat and chemical satiability
- Cost-effective
Administration
- Oral
- Rectal
- IV
- IA
- Filling a space or cavity (cavity, bladder, intrathecal space, gall bladder etc)
phase contrast can be used to
detect blockages or tears e.g. in the bowel (e.g. perforation of bowel)
Excretion of phase contrast
- Glomerular filtration (95%)
- Important kidneys are working
- Tubular excretion and protein being negligible
- Half life: 30-60 minutes
Side effects of phase contrast
- Reactions due to osmolality
- Endothelial damage
- Thrombosis and thrombophlebitis
- Vasodilation
- Vasodilation
- Vascular pain
Idiosyncratic reactions
Cant predict (within 30 mins)
- Mild (most- rash etc~)
- Moderate
- Severe (0.03%)- very rare
Nonidiosyncratic reactions
( beyond 30 mins to 7 days)
- Cardiac
- Nephrogenic
- Extravasations
how do patient do a gluorscopy
Patients swallow contract (barium, iodine, gadolinium (MRI))
Strongly absorbs X-any dense white
Any space it can be swallowed, inserted or injected
fluoroscopy used in
- Angiography
- Contrast GI studies
- Therapeutic joint injection
- Arthrograms
- Screening in theatre
advanatges of fluoroscopy
- Cheap
- Dynamic
- Interventional procedures e.g. stunting
disadvantages of fluorscopy
radiation
systemic approach of reading an X-ray e.g.
Date taken
Patient demographic
Penetration- are we using the correct amount of energy beams to get good photo
View- how the X-ray beams pass through the patients (PA/AP/ lateral)
Rotation- how the patient is positioned
how to read a chest X-ray (CXR)
A-Airways -trachea and bronchi
B-Breathing- lungs should be black. Trace all the way around the edge- can you see the nice angels
C-Circulation- the heart and aorta. Should see the heart easily- white
D-Disability- bone
E-Everything else- tubes and lines
how to a read an abdominal x-ray (AXR)
A-Air
B-Bowel
a. Small bowel
b. Large bowl
D-Densities (bone)
O- Organs
fractures =
displacements
bone abnormality
bone qaulity (lytic, sclerotic, mixed)
advantages of X-ray
Advantages
Quick
Portable
Cheap
Simple
disadvantages of X-rays
Disadvantages
Radiation
One plane so 2D
Would not see all pathology
Cant visualise all areas
Poor soft tissue imaging
uses of X-rays
- Chest
- Infection, pneumothorax, trauma, effusion, oedema
- Bowel
- Dilation, perforation
- Orthopaedic
- Fracture, trauma
- Post-procedure
- Nasogastric tube, pacemaker
- Dentist
CT (computed tomography) uses what machinary
Uses rotating gantry
X-ray tub on one side
Detectors on the other
how does a CT give a detailed image
Lots of slices of images up together by computer- same principle of attenuation as X-ray
Usually transverse images
density in CT measured in
hounsfield units
advantages of CT scan
- Quick
- Good spatial resolution
- Can scan most areas (not all)
disadvantages of CT scan
Radiation
Lower contrast resolution
Affected by artefact
Requires breath holding (not all patient can manage)
Overuse (fishing for diagnosis)
Incidental findings
CT scan uses
Diagnosis- cancer, stroke, bony injury, blood flow
Guide further tests or treatment- radiotherapy, biopsy
Monitor conditions e.g. cancer treatment
MRI (magnetic resonance imaging) uses…
magnetic field instead of X-ray
How does MRI work
- Relies on narrow gantry
- Uses a strong magnetic field
- Image quality relies on magnetic field
- Aligns hydrogen atoms
- Some point towards the head and some towards the feed
- Not 50/50
- Unmatched ions remain
- Radiofrequency pulse applied
- Unmatched ions absorb energy and spin in different directions
- Pulse is turned off and atoms spin returns which emits energy
- Computer processing to generate image.
in M RI different relaxations produce different
weighting from tissues
T1 weigthing
fat is white
water is black
T2 weighting
water is white
fat is black
white
high signal
black
low signal
uses of MRI
CNS - brain and spinal cord
Bones and joints
Heart and blood vessels
Internal organs
Advantages of MRI
- no radiation
- Good contract resolution
Disadvantages
- Time consuming
- Expensive
- Limited availability
- Some patients won’t fit
- Claustrophobic
- Loud
- Need to lie still
- Metalwork
scintigraphy (nuclear medicine)
- Injection radiopharmaceuticals
- Emit gamma rays which an be detected
- Highly sensitive
- Functional and anatomical info
example of imaging that uses scintigraphy
Positron emission tomography (PET)
PET scan overview
- Radionuclides that decay by positron emission
- Bound to glucose
- PET cameras detect high energy gamma rays (annihilations) - the more annhiliation the bigger the signal
- Used in combination with CT/ MRI
- Hot spots= areas of high glucose metabolism (heavily used in oncology)
how do ultrasounds work
- High frequency sound waves from transducer probe
- This sound wave is reflected back by tissues where densities (impedance) differs
- Probe defects reflected sound waves
Creates electrical signal
- Determines distance- time taken to come back
- Determine impedance- proportion of reflected waves
in US hyperchoic
more reflective= white
in US hypoechoic
less reflective= dark grey
in US anechoic
not reflective (pure fluid (black))
duplex ultrasound
= 2D and doppler
uses of ultrasound
- Can be used in body cavities e.g. transvaginal, transrectal and transoesophageal
- Solid organs- liver, kidney, spleen, pancreas, thyroid
- Urinary tract- stone, dilation, volume
- Obs and gynae- pregnancy and uterus
- Musculoskeletal
advantages of ultrasound
- Lacks ionising radiation
- Low cost
- Portable
- Can be inserted into body cavities
- Babies
- Dynamic (blood flow)
disadvanatges of ultrasound
- Operator dependant
- No bone or gas penetration
- Body habitus
myelination in peripheral neurones
1) Axon sitting in a groove surrounded by a schwann cell
2) Mesaxon membrane initiates myelination by surrounding the embedded axon
3) A sheet-like extension of the mesoaxon membrane then wraps successively around the axon- forming multiple membrane layers
4) Cytoplasm is extruded between the two apposing plasma memebranes of the schwann cell, which become compacted to form myelin (19-20 round)
outer mesaxon
invaginated plasma membrane extending from the aboaxonal surface of the schwann cell to the myelin
inner mesaxon
extends from the adaxonal surface of the schwann cell (part facing the axon) to the myelin
oligodendrocytes
- Does the same thing as shwann cell but in the CNS
- Cytoplasmic processes from the oligodendrocyte cell body to form flattened cytoplasmic sheaths that wrap around each of the axons
difference between oligodendrocytes and schwann cells
wraps around more than one axon simultaneously
Unmyelinated nerve cells
Slower propagation of action potential
support cells of the CNS
- oligodendrocytes
- astroctes
- microglial cells
- ependymal cells
astrocytes
- Star-like structure
- Have ‘perineural feet’ that contain gap junctions
- Biochemical support for endothelial cells
- Transport of nutrients (lactate) from blood to nerve cells
- Regulate nerve impulses by releasing glutamate
- Contribute to the BBB
microglial cells
- Large cell with elongated nucleus and relatively few processes emanating from cell body
- Found throughout the CNS
- Resident macrophages
- Immune function
- Remove damaged nerve cells
- Digest protein tangles associated with senile dementia and Alz
- Sense increase K+ ions
ependymal cells
- Line the spinal canal and the ventricular of the brain
- Look like columnar epithelial cell lining of spinal canal and ventricles (CSF) of the brain
- Joined by junction complex (JC) that separates the lumen of the canal from the lateral intercellular space
- Apical surface has both cilia and microvilli
- Function:
- Synthesise and secrete CSF in the ventricles
- Cilia move CSF through ventricles to the spinal cord
- Microvilli absorb CSF for removal of pathogens
- Present pathogens to microglial cells and astrocytes
- Modified tight junctions between epithelial cells control fluid release into the brain
Mulitiple sclerosis
- Remitting and relapsing disease
- Degenerative
- Caused by autoimmune degradation of myelin
- Symptoms caused by loss of conduction velocity
symptoms of MS
fatigue, vision problems (Diplopoda), slurred speech (dysarthria), numbness and tingling sensation (paraesthesis), mobility issues (muscle spasms), urinary retention, constipation
