Radiography (Diagnostic Radiology)

Question 1

Equation for magnification

Answer 1

SID / SOD

Question 2

What color resembles greater optical density, white or black?

What about greater relative exposure?

Answer 2

Black for both

Question 3

Equation for transmittance

Answer 3

T = I / I₀

Question 4

Equation relating optical density to transmittance

Answer 4

OD = -log₁₀T

or

T = 10^-OD

Question 5

What does the reciprocity law state and when is it not true?

Answer 5

Relationship between exposure and OD should remain constant regardless of exposure rate.

Fails at long and short exposure times. OD is not constant

Question 6

On the Hunter and Driffield curve, what represents the film contrast?

Answer 6

Steepness (average gradient) of the linear region.

Makes sense, for a change of exposure, there should be a greater change in OD

Question 7

What regions of the H&D curve have poor contract (small slopes on the curve)

Answer 7

Toe and Shoulder region

Question 8

What is the usuable range of the H&D curve? What is the range of x-ray exposures within this usuable range?

Answer 8

Usuable range: Area where exposure and OD are linearly related

Latitude gives the exposure range

Question 9

Fast films require __________ exposure to achieve a given OD

(more or less)

Answer 9

Less exposure

Question 10

Faster SF systems result in lower patient dose, but in general exhibit more ____________

Answer 10

Quantum noise

Question 11

By how much does using film-sceen versus film only reduce the radiation dose to the patient?

Answer 11

By up to 50x!

Much more x-rays are detected. Resolution is degraded though

Question 12

What is the conversion efficiency of a phosphor?

Answer 12

Fraction of absorbed energy emitted as UV or visible light

Question 13

Difference between Conversion efficiency (CE) and absorprtion efficiency (QDE)

Answer 13

CE - ability of screen to convert energy deposited by absorbed x-rays into film darkening

QDE - how efficiency the screen detects the x-ray photons incident upon it

Question 14

Main difference between direct and indirect digital film

Answer 14

Direct: signal comes straight from the beam x-rays

Indirect: there is an intermediate conversion step

Question 15

Which of these are untrue about digital

Answer 15

Wider dynamic range than screen film

Reduces repeat rates

Higher patient throughput but lower dose efficiency

No consumables

Question 16

How many bits are in a byte?

Answer 16

8

Question 17

Equation for bit depth

Answer 17

2ⁿ

where n is the number of bits

Question 18

What is the difference between the H&D curve of digital detectors vs analog?

Answer 18

Digital holds the linearity much longer than analog

Question 19

Remember, resolution is always defined by the bigger dimension.

Answer 19

Example, you have 1000 lp

for a 24 x 30 cm plate

resolution = 1000 lp/ 300 mm = 3.3 lp/mm

Question 20

What is the process in which a laser scans a imaging plate and PSP processes data?

Answer 20

Computed Radiography

Question 21

Which of the following is not a posisble cause of blurring at the borders of high contrast objects?

Large focal spot

Patient motion

High magnification

Answer 21

Trick question, they all are

Question 22

What is the major concern of optical coupling?

Optical coupling: occurs from a gap between scintillator and focusing lens to detector

Answer 22

Large loss of light!

Question 23

What is the fill factor of a thin-film transistor

Answer 23

Light sensitive area / detector element area

Question 24

Which gives better absorption, thick or thin screen?

What about better resolution?

Answer 24

Better absorption - Thick screen

Better resolution - Thin screen

Question 25

If 2 mGy of dose is delivered to the surface, approximately how much is delivered to center of chest? What about posterior end?

Answer 25

0. 22 mGy to center
1. 02 mGy to other side

Question 26

What is the relationship between output kerma and typical x-ray tube voltages?

Answer 26

Roughly linear. Maybe slightly exponential

Question 27

Dose at depth d in a patient given entrance skin dose, SSD and attenuation coefficient

Answer 27

D_d = ESD e^-µd (SSD/(SSD+d))²