Radiology part 1 Flashcards
-ves of nuclear medicine as an imaging modality?
uses radioactive material so could be of danger to the patient
how is nuclear medicine used in imaging?
Uses tiny amounts of radioactive material
Incorporated into compounds or pharmaceuticals
Distribution in the human body can be visualised
different types of nuclear medicine used in imaging?
scintigraphy
Single Photon Emission Computed Tomography (SPECT)
Positron Emission Tomography (PET)
what is scintigraphy?
type of nuclear medicine where a plain 2-D image produced, could do an 123iodine scan for hyper/hypothyroidism
what is single photon emission CT
type of nuclear medicine which uses a gamma-ray emitting radiopharmaceutical to produce a 3-D picture e.g. 99 Technetium cardiac SPECT scan
describe positron emission tomography
Uses an beta-particle emitting radiopharmaceutical
Beta particle decays to emit an electron and a positron
3-D picture produced
time taken for positron to be detected- can work out where abnormalities are e.g. can detect abnormal glucose met. in tumour-Fluoro-Deoxy Glucose (FDG)
PET scan showing metastatic disease in the liver.
advantage of optical imaging over US?
uses higher frequency (tetrahz compared to megahz) so higher resolution images produced
use of optical imaging?
uses visible light e.g. Microscopy analysis of tumour sections (histopathology) and optical coherence tomography (OCT) e.g. to visualise the retina
how does the modern X-ray tube work?
this is a vacuum tube that produces X-rays. They are used in X-ray generators. X-rays are part of the electromagnetic spectrum, an ionizing radiation with wavelengths shorter than ultraviolet light. e- decelerate within the tube as they move towards the target which allows the production of an image.
what does X-ray absorption depend on?
tube voltage- potential difference between anode and cathode
anode material
atomic no. of absorbing matter- higher number= greater absorption factor of material, and more absorption= appears white= denser materials
-ves of X-rays
use of ionising radiation
BUT radiation of 1 chest X-ray is only 3% of the natural background radiation we are exposed to in a year
however, body CT scan is 3 times as much radiation as the natural radiation we are exposed to in a year
how does a CT scanner work?
use of an X-ray tube
X-ray source rotates around patient
X-rays detected and used to produce an image on a computer screen
set of 1D measurements in each location combine to produce a 2D reconstruction of the patient
256 slices can be produced in a second
able to visualise change in density between structures- based on anotomic no. (higher no.=more dense)
advantages of CT over MRI?
greater spacial resolution- so smaller structures can be distinguished, so size of the smallest structure that can be distinguished used CT is smaller than that using MRI
BUT CT uses ionising radiation- this carries an increased risk of cancer
how is the signal produced in MRI?
signal comes from within the patient: from a nucleus- contained by an atom alongside orbiting electrons, nucleus consists of protons and neutrons which have a ‘spin’ and a ‘spinning’ charge gives a magnetic field
Some nuclei - including that of hydrogen - are paramagnetic so are only magnetised when a magnetic field is applied. So once applied, nuclear spinning occurs and the magnetics of the nucleus are detected
so superconducting magnet used with coils: Coils made from niobium / tin alloy, filled with liquid helium at 4.2 Kelvin, and giant vacuum flask to repel heat.
magnet= strength=tesla- typically 1.5-3.0
there’s a magnetic field gradient so the field strength is varied across the patient and the signal frequency tells you where it has come from
advantages of MRI over CT?
doesn’t use ionising radiation that increases cancer risk
produces a better contrast despite not as good spacial resolution
is detail of CT or MRI scan better and why?
CT as better spacial resolution so size of smallest structure that can be distinguished is smaller than for MR
what does tighter coil in superconducting magnet mean for MRI?
better reception of signal so better image produced
costs of CT and MRI?
increased, now £600,000 for CT and £800,000 for MRI
why do we perform radiological tests?
To “look inside” the patient.
To rule out or confirm a suspected condition.
Because the patient expects it
what is Baye’s theorem?
Bayes’ theorem is a way to update probabilities based on new evidence. Here ‘proposition A’ is a hypothesis H. E is the evidence.
P(H|E) = the probability that the hypothesis H is true, given some new evidence E.
what is the Doppler equation?
Fd= 2Vftcostheta/c
V = velocity of blood
2 = have to multiply signal by 2 as the signal goes to the object and then returns
C = constant
o Speed of sound within tissue (1540)
Ft = frequency of the transducers
Θ = angle of transducer to the angle of blood flow
o Angle of probe effects how the signal appears
o Angle correction cursors must be set properly
Alters velocity of blood flow otherwise
o NB: if Θ = 90, cosΘ = 0
Therefore there will be no Doppler signal and no noise
what is the odds ratio?
OR = P(H)/ (1-P(H))
note that P(H) = OR /(1+OR)
what is the likelihood ratio?
LR = P(E|H) / P(E|H’)
what is Baye’s theorem in terms of OR and LR?
posterior OR after evidence= prior OR x LR
so posterior OR= P(H I E)/ 1-P(H I E)
and this equals the prior OR= P(H)/1-P(H)
multiplied by the LR= P( E I H)/ P(E|H’)
