Anatomy Imaging Flashcards
what is an X-ray, what is it used for and what are the pros/cons
X-rays are a form of electromagnetic radiation, similar to visible light. Unlike light, however, x-rays have higher energy and can pass through most objects, including the body.
Useful for visualising the skeletal system and some disease processes in soft tissue.
A heterogeneous beam of X-rays (gamma radiation)
Based on the density and composition of the structure a proportion of the X-rays will be absorbed
The X-rays that pass through are detected as black areas and indicate less dense tissues
Grey/white areas are denser tissues that have absorbed more X-rays
pros:
Cheap
Readily available
cons:
Uses ionising radiation (can cause DNA mutation)
Limited range of densities
Air = black
Fat = light grey
Soft tissue/fluid = shades of grey
Calcium = most dense naturally occurring tissue
Metal = white
* 2D representation of a 3D object (cuz we are 3D lol e.g. u can’t see sternum)
are most X rays we do AP or PA; when would we use the abnormal view?
we normally use PA; posterior to anterior direction (emitter is behind u and detector at front)
UNLESS U WANT A CHEST X RAY then you will do AP (anterior to posterior direction; emitter is infront of u)
heart looks bigger in an AP
we also use AP when patient is bed ridden or an infant
for the appendicular skeleton do we use an AP or PA X-ray?
for the appendicular skeleton AP (anterior posterior) and lateral views most common
what is situs inversus totalis
This is situs inversus totalis = the person has everything on the other side
congenital condition in which the major visceral organs are reversed or mirrored from their normal positions.
what is a DEXA scan; what does it stand for
DEXA scan (Dual energy X-ray absorptiometry)
- Two different low energy X-ray sources
- The denser the bone the fewer X-rays that get to the detector
- Using 2 different (lower energy) X-ray sources improves accuracy
what is a CT scan; pros + cons
uses similar technology to X-ray, but it rotates around with multiple X-ray sources; it takes a cross section through body
Uses multiple x-ray beams at different angles to build up a cross section of the body’s organs and tissues
Advantages :
* Cross-sectional images and other planes can be reconstructed afterwards or 3D reconstructions
* Good high contrast bone detail
* Well tolerated (not scary for patient)
* Readily available
Disadvantages :
* Ionising radiation dose
* Metallic artefacts cause loss of detail
* Soft tissue surrounded closely by bone difficult to image
* Respiratory movement artefact
what is an MRI; pros/cons
MRIs basically measure the amount of water in a tissue in a v specific way
Uses non-ionising radiation
10,000 – 30,000 times the earths magnetic field (H+ ions are gonna be orientated in one direction during MRI and then when u turn off machine we look at how fast the H+ ions take to rearrange themselves)
Very high soft tissue contrast
Images acquired in transverse plane (patient passes through the MRI lying down)
Can be reconstructed in any plane
Can get both structural and functional information
Does not image bone directly
When radiofrequency pulse switched off T1 relaxation occurs (longitudinal magnetisation increases. T1 images are usually used to look at normal anatomical details.
Simultaneously something changes in the transversal plane (protons spinning synchronously will no longer spin synchronously when radiofrequency pulses (RF) switched off. T2 is the transverse movement of protons and is usually used to look at pathology because most tissues involved in disease tend to have a higher water content than normal.
cons:
* v loud + claustrophobic
* can’t wear anything metal as that will come swinging out (so no earrings) most pacemakers and things are made out of non-magnetic things nowadays but u must check
what is an ultrasound?
Based on sound waves with frequencies usually in range of 1-18megahertz
used to look at developing fetus, flow of blood in arteries/veins, use it to guide when ur taking a fluid sample e.g. from a swollen knee so u dont hit an important blood vessel
pros:
Safe during fetal development as no radiation
Cheap
Readily available
Becoming more common for both diagnosis and therapeutic imaging
con:
But difficult to interpret what is going on unless u know what you’re looking for
what contrast media do we use?
barium, iodine, + gadolinium
gadolinium is used exclusively for MRI; its good for seeing tumours
do not want to inhale these usually used as enema for GI tract, sometimes given as swallow but again dangerous as can kill the alveoli
