3 - Introduction to Imaging Flashcards
What should I know?
- How x rays are made
- The 2 main densities on x ray exams
- Which radiology exams use x rays
- Understand some of the other techniques used for investigations i.e. us, ct, nm, mri, pet
What did the discovery of x rays follow
Electricity, magnetism and importantly the ability to produce a vacuum within a glass tube
What 4 things does an x ray tube consist of?
- An electron source (the cathode)
- A strong accelerating force
- A vacuum within a glass (no air)
- Tungsten focal spot that creates x rays upon impact (the anode)
What are the 2 types of radiation created when tungston is bombarded with electrons?
- Braking Radiation (the e- whirls around the nuclei and is bent)
- Characterestic Radiation (e- hits another e- to an outer level)
The energy given off by these forms x rays
Wavelength of xrays?
0.01nm - 0.1nm
Only gamma rays are shorter
When first discovered how did they enhance xrays
They put a photosensitive source under the body part and subsequently saw the shadows of bones
What kind of radiation is xrays
electromagnetic
What initially happened when people used xrays without control
Radio-necrosis
Was 5 years until it what recognised as dangerous
Grid?
Ensures that only the direct rays make it through to the film and the ones at weird angles that would blur the film are bounced out
What are the 4 x ray density levels (important)
- Calcium (bone) - white
- Water (tissue) - grey
- Fat - darker grey
- Air (lung/fundus) - black
What is the 5th density
Metal. Shows as white i.e. medical tools
How are x rays made
- play a high electrical potential across and evacuated tube and pass a current through it
- the resulting x rays penetrate tissue and densities to varying degrees and creates shadows
Why is viewing soft tissue structures less successful in xray
The difference in density and penetration and so shadowing of middle level tissues (fat, tissues, blood) is small
How may an x ray contrast be improved
Using less voltage like in a mammograph
Difference between radiographer and radiologist
grapher - takes x ray (medical imaging technologist)
ologist - interprets the x rays
X ray diagnosis (pros and cons)
- good spatial resolution
- limited contrast resolution
- depicts differences in density via ranges of greys
- can age and stage kids wrists
How many views do you do
at least 2 of every bone
Why does the heart look radio opaque?
Bones behind it
What does pneumonia look like on an x ray
Opaque (shouldn’t as should be filled with air and be black). Takes out whole lobe while a mass is more well defined (also get weight loss with a tumour)
Completely white lungs?
Drowned and filled with water
What does a pneumothorax look like
Air in pleural space so looks like lung has collapsed. If it is filled with fluid it is called a hydropneumothorax
What is a pleural effusion?
Excess fluid build up around the lung. Looks like a great big white opacity at the bottom of the lung
4 ways to increase contrast in x ray
- Barium sulphate
- Iodine
- Gadolinium (MRI)
- Air
Barium Sulphate
Given by mouth, injected into gut, up rear (enemas) GI studies, no one is allergic to barium some people are allergic to iodine. Can see ulcers
Iodine
Injected into BVs (angiography). 1/40 000 people die from iodine. Excreted by kidney so good to view.
Plain x rays and ct to enhance vessels and kidney
Gadolinium
MRI. Injected. Used as iodine isn’t good in a magnet
Air
Brain (encephalograms) - used to make air go into brain. Not used anymore as high mortality
Haematuria?
RBCs in urine
Presentation of kidney stones?
- groins pain and haematuria
- inject iodine
- US in young CT in old
Why use an angiogram?
With iodine. See if vessels still patent
Nuclear medicine
- radioactive substances are ingested or injected
- gamma rays detected using a gamma camera
- bone scans (goes to osteoblasts), thyroid scans, lung scans
- head (stroke), bone, lung, thyroid, renal
Ultrasound
- short pulses of sound waves
- piezo-electric crystal
- images by the transmission or reflection of waves
- inexpensive, safe, portable
- but can’t penetrate bone and air containing structures
How much does a US machine cost
more than $1 million probes $10 000
US
- produces 2d or 3d images
- the location is determined by the time taken to receive the reflected signal
- appearance is determined by differences in tissue impedence (Z)
Z = pc
In US what colour are vessels and the GB
Fluid is black as no sound waves reflected
What is US used for
abdominal pain LFT bumps/mass swelling renal dysfunction vascular imaging cancer screening pregnancy children pelvic pain ovarian pathology scrotum
CT (computed tomography)
- xrays in transverse plain
- cross sectional imaging
- LESS spatial resolution than x ray but much better contrast resolution
- added contrast with iodine
- 300 xrays
- blood is white
- bowel obstruction
- go to first for trauma
When would you do a head ct
headache, dizziness, hemiplegia (paralysis on one side of body), trauma
- may be a haemorrhage (sudden severe headache and vomiting
)
When would you do abd ct
- when us not helpful
- trauma
- cancer
- bowel obstruction
- vascular imaging
Magnetic Resonance Imaging (MRI)
- uses magnetism in any plane
- hydrogen nuclei within the body align with the mag field
- added radiofrequency pulses change this alignment and energy is released when the protons realign to the mag field
- no radiation
- good brain pics
- renal cancer
- BOTH good spatial and contrast resolution
- can get 3D images in any plane
- expensive and takes a long time to set up and image
- availability
- contradictions (pacemakers, claustraphobia)
- gadolinium used to increase contrast
PET imaging
- die with radioactive tracers
- injected into veins
- cancer soaks up and shows bright node at metastases
- ## short 1/2 life
