Chapter 7 RADR 1313

The product of milliamperage and exposure time is what in relation to the quantity of x-rays produced?

Directly proportional.

As mAs increases, what happens to the quantity of radiation reaching the IR?

Increases.

If you select 250 mA and 0.5 seconds, how much mAs is created?

125 mAs. Equation: mAs = mA × time = 250 × 0.5 = 125 mAs.

Original exposure: 100 mA at 125 ms. Which techniques decrease IR exposure by about half?

All of the above: 200 mA at 31 ms, 100 mA at 0.063 seconds, and 50 mA at 0.125 seconds. Original = 12.5 mAs; half ≈ 6.25 mAs.

Original technique: 300 mA at 50 ms. If mA increases to 500, what exposure time maintains the same IR exposure?

0.030 seconds (30 ms). Original mAs = 300 × 0.050 = 15 mAs; time = 15 ÷ 500 = 0.030 seconds.

Original technique: 50 mA at 0.20 seconds. Which techniques maintain the same IR exposure?

All options: 100 mA at 0.10 seconds, 200 mA at 0.05 seconds, and 400 mA at 0.025 seconds. Each produces 10 mAs.

Does mAs directly control the brightness of a displayed digital image?

No. mAs does not directly control displayed brightness.

When is increased quantum noise seen in a digital image?

When mAs is severely lower than needed.

What numerical value displayed on a processed image indicates the x-ray exposure received by the digital IR?

Exposure indicator (EI).

If the exposure indicator shows too little radiation at the IR and the image has increased quantum noise, what technique change is best on repeat?

Increase kVp by 15% or double the mAs.

Which technical factor affects IR exposure by altering the amount and penetrating ability of the x-ray beam?

kVp.

To reduce patient exposure, which exposure factors should be considered?

Higher kVp and lower mAs.

What does a high kVp result in regarding x-ray intensities exiting the patient?

Less variation in the x-ray intensities exiting the patient.

How much of a change in kVp changes IR exposure by a factor of two?

15%. A 15% increase approximately doubles exposure; a 15% decrease approximately halves exposure.

Original technique: 80 kVp at 20 mAs. If kVp increases to 92, what mAs maintains IR exposure?

10 mAs. A 15% kVp increase approximately doubles exposure, so halve mAs: 20 ÷ 2 = 10 mAs.

Original technique: 80 kVp at 20 mAs. If kVp decreases to 68, what mAs maintains IR exposure?

40 mAs. A 15% kVp decrease approximately halves exposure, so double mAs: 20 × 2 = 40 mAs.

When selecting focal spot size, what is the radiographer really determining?

The actual size of the filament used.

What is the distance between the radiation source and the image receptor called?

SID (source-to-image-receptor distance).

What law states that beam intensity is inversely proportional to the square of the distance from the source?

The inverse square law. Equation: I₂ = I₁ × (D₁/D₂)².

At 3 ft, exposure is 160 mR. What is the exposure at 6 ft?

40 mR. Equation: I₂ = 160 × (3/6)² = 40 mR.

At 3 m, exposure is 1 mGy. What is the exposure at 1 m?

9 mGy. Equation: I₂ = 1 × (3/1)² = 9 mGy.

What is the distance between the object being imaged and the image receptor called?

OID (object-to-image-receptor distance).

What is SID divided by SOD called?

Magnification factor (MF). Equation: MF = SID ÷ SOD.

A chest image uses 180 cm SID and 12 mAs. At 100 cm SID, what mAs maintains IR exposure?

Approximately 4 mAs. Equation: mAs₂ = 12 × (100/180)² ≈ 3.7 mAs ≈ 4 mAs.

A quality image uses 10 mAs, 70 kVp, and a 12:1 grid. What mAs gives similar IR exposure with the grid removed?

2 mAs, according to the study guide. Divide 10 mAs by 5.

Original technique: 80 kVp at 20 mAs with an 8:1 grid. What mAs is needed with a 16:1 grid?

30 mAs, according to the study guide. Equation: 20 × (6/4) = 30 mAs.

What is the misrepresentation of the size of an object called?

Magnification.

To minimize magnification of an anterior structure, which projection is best?

Posterior-anterior (PA).

Which factor affects magnification according to the study guide's answer?

SID (source-to-image-receptor distance).

What property do digital image receptors have that improves visualization of soft-tissue structures?

Excellent contrast resolution.

How can shape distortion be created?

By decreasing SOD and angling the central ray.

How can SOD be calculated?

Subtract OID from SID. Equation: SOD = SID − OID.

What effect does increasing SID have on spatial resolution?

Increased spatial resolution.

For every how much increase in part thickness should mAs be adjusted by a factor of two?

Every 4 to 5 cm.

A foot image uses 4 mAs at 100 cm SID. At 125 cm SID, what mAs maintains IR exposure?

6.25 mAs by calculation, approximately 6 mAs. Equation: 4 × (125/100)² = 6.25 mAs.

Assuming all techniques produce diagnostic images, what is best for an infant chest radiograph?

Use a 40 ms exposure time.

Which body habitus requires the highest exposure factors?

Hypersthenic.

What property of the x-ray beam impacts image unsharpness?

Beam divergence.

Once the part has been penetrated, what happens to IR exposure when mAs is doubled?

IR exposure doubles.

Which mA/time combination does not produce 12 mAs?

800 mA at 0.15 seconds. Equation: 800 × 0.15 = 120 mAs, not 12 mAs.

If lower-than-needed kVp is selected, what will the digital image demonstrate?

Higher subject contrast and increased quantum noise.

What happens when twice as much mAs as needed is used?

Adequate displayed image brightness but unnecessary patient radiation exposure.

6 mAs is appropriate for a knee at 100 cm SID. How much mAs is needed at 140 cm SID?

Approximately 12 mAs. Equation: 6 × (140/100)² = 11.76 mAs ≈ 12 mAs.

Which image characteristic is not affected by a change in SID, according to the study guide?

Image contrast.

Where is the radiographic grid located?

Between the patient and the image receptor (IR).

What happens when collimation is decreased, creating a larger field size?

All options are correct, according to the study guide.

What happens to the x-ray beam when tube filtration is increased?

Fewer photons and higher average energy.

Compared with a 24 cm abdomen, what results from imaging a 20 cm abdomen?

All options are correct, according to the study guide.

True or false: Increasing part thickness decreases image contrast.

True.

True or false: kVp does not affect the quantity of exit radiation until adequate penetration is reached.

True.

True or false: The amount of mAs used controls displayed image brightness.

False.

True or false: Changes in kVp do not affect the exposure indicator value.

False.

True or false: Any increase in magnification results in a decrease in spatial resolution.

True.

True or false: When choosing a grid, the grid with the highest ratio should always be selected to improve contrast.

False.

True or false: Compared with a three-phase unit, a single-phase x-ray unit requires higher exposure techniques for a comparable image.

True.

True or false: The same mAs and kVp should be used for AP and lateral lumbar spine images.

False.

True or false: OID affects magnification, spatial resolution, contrast, and exposure to the IR.

True, according to the study guide.

True or false: To reduce patient radiation exposure, it is best to use lower kVp and higher mAs.

False.