Section 4&5 Flashcards
What are the 3 components of visual perception?
Detection, recognition, interpretation
What is the structure of truth table
positive negative, true diagonal and false diagonal
Sensitivity
true positive = # pt diag/disease present (TP + FN)
Specificity
true negative = # pt correctly identified as no disease//# without the disease
Accuracy
correct diagnosis of disease present in patients (TN + TP) //total
Prevalence
patients with disease present -TP + FN// total
What are the components of instrument?
source, medium, filter, detector, signal processing
Current =
amount of charge flowing at a point per unit time
Voltage =
energy difference between 2 points
Fundamental idea in Band theory
Photon absorption provides energy to electrons to be excited. This causes the electron to sit in the conduction band. As it de-excites, it emits a photon to fall into valence band
Scintillation –>
radiation into light
Detectors have 3 factors
Intrinsic efficiency/sensitivity
dead time
energy discrimination
Intrinsic efficiency (sensitivity)
photons detected//#photons incident to detector
- faster image & reduced dose
Dead time is
the amount of time for the detector to record an event and resent ready for next event
Paralysable
event is missed so the detector restarts dead time after every miss - very saturated fast - slows/paralyses its measurements
Non-paralysable
does not extend its time - just misses event and keeps going - higher rates can be measured
Energy discrimination is
the ability to distinguish photons of different energies - measured at full width at half maximum
Energy discrimination in detectors helps with
filtering out low scattered radiation
In scintillation detector, photomultiplier tube is
responsible for converting light into electrical signals
In scintillation detector, crystal density affects
the ability to convert radiation, as more interactions occur frequently and more light is produced - probability is higher and efficiency is increased
