Digitial Numbers

What is the mAs formula?

mAs = mA × time (seconds)

How do you solve for exposure time from mAs and mA?

Time = mAs ÷ mA

What is Ohm’s law?

V = I × R

What is the electrical power formula?

P = V × I

What is the transformer voltage/turns relationship?

Vs ÷ Vp = Ns ÷ Np

What is the inverse square law?

I₁ ÷ I₂ = D₂² ÷ D₁²

What formula maintains receptor exposure when SID changes?

mAs₁ ÷ mAs₂ = SID₁² ÷ SID₂²

What is the magnification factor formula?

MF = SID ÷ SOD

How can magnification factor be calculated from image and object size?

MF = image size ÷ object size

How are SID, SOD, and OID related?

SOD = SID − OID

What is the pixel-size formula?

Pixel size = FOV ÷ matrix; convert FOV to mm first

What is the Nyquist frequency formula?

Nyquist frequency = sampling frequency ÷ 2

How can Nyquist frequency be calculated from pixel pitch?

Nyquist = 1 ÷ (2 × pixel pitch)

What is grid ratio?

Grid ratio = H ÷ D; lead-strip height ÷ interspace width

What formula is used when changing grids?

New mAs = old mAs × (new GCF ÷ old GCF)

What is the grid conversion factor with no grid?

1

What is the common grid conversion factor for a 5:1 grid?

2

What is the common grid conversion factor for a 6:1 grid?

3

What is the common grid conversion factor for an 8:1 grid?

4

What is the common grid conversion factor for a 10:1 or 12:1 grid?

5

What is the common grid conversion factor for a 16:1 grid?

6

What grid conversion factor did Mosby use for a 12:1 grid?

5

A nongrid technique uses 10 mAs. What mAs is needed with a 12:1 grid, GCF 5?

50 mAs

What is the 15% rule when kVp is increased 15%?

Halve the mAs to maintain receptor exposure

What is the 15% rule when kVp is decreased 15%?

Double the mAs to maintain receptor exposure

If kVp increases 15% and mAs stays unchanged, what happens to receptor exposure?

It approximately doubles

If kVp decreases 15% and mAs stays unchanged, what happens to receptor exposure?

It is approximately halved

On a variable-kVp technique chart, about how much is kVp changed per cm?

About 2 kVp per cm

What is the heat-unit formula?

HU = kVp × mA × time × generator factor

What generator factor is used for single-phase equipment?

1.0

What generator factor is used for 3-phase 6-pulse equipment?

1.35

What generator factor is used for 3-phase 12-pulse equipment?

1.41

What generator factor is commonly used for high-frequency equipment?

1.45

What is the first step in an HVL calculation?

Number of HVLs = total thickness ÷ HVL

What fraction remains after n HVLs?

Fraction remaining = (1/2)ⁿ

How much radiation remains after 1 HVL?

50%

How much radiation remains after 2 HVLs?

25%

How much radiation remains after 3 HVLs?

12.5%

How much radiation remains after 4 HVLs?

6.25%

What is the minification-gain formula for an image intensifier?

Minification gain = (input phosphor diameter ÷ output phosphor diameter)²

What is the brightness-gain formula?

Brightness gain = minification gain × flux gain

What is the flux-gain relationship?

Flux gain = output light photons ÷ absorbed input x-ray photons

What is the DSA subtraction relationship?

Contrast image − mask image = subtracted image

What is the CR alignment/congruency tolerance?

Within ±1% of SID

What is the light-field to radiation-field alignment tolerance?

Within ±2% of SID

What is the maximum digital spatial-resolution QC image blur?

No more than 2%

What is the kVp accuracy tolerance?

Within ±5% of indicated kVp

What is the timer accuracy tolerance for exposures over 10 ms?

Within 5%

What is the exposure reproducibility tolerance?

Repeated exposures should not vary by more than 5%

What is the AEC detector calibration tolerance?

Within ±5%

What is the exposure linearity tolerance between adjacent mA stations?

Within 10% of one another

What is the monitor luminance uniformity tolerance?

Readings should be within 20% of one another

What is the effective focal-spot size tolerance in the Mosby material?

Within 50% of the stated equipment specification

What fluoroscopy exposure-rate limit was listed on the Mosby page reviewed?

No more than 100 mGy/min

What is the CR plate-uniformity brightness tolerance in the Mosby material?

Areas should be within ±0.2 of each other

At about what part thickness does Mosby recommend grid use?

About 10 cm or greater

Above approximately what kVp does Mosby recommend grid use?

Greater than about 60 kVp

What total filtration is generally required above 70 kVp?

At least 2.5 mm aluminum equivalent

What is the heel-effect anchor?

Small anode angle + short SID + large field = stronger heel effect

What happens to effective focal spot as anode angle decreases?

Effective focal spot decreases

What is the line-focus principle?

Large actual focal spot for heat + small effective focal spot for detail

What are the approximate voltage-ripple values?

Single-phase 100%; 6-pulse 14%; 12-pulse 4%; high-frequency ~1%