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Entrance Skin Exposure (ESE) is the measurement of radiation output at the point of skin entry for common X-ray examinations, including fluoroscopic and conventional radiology. Traditionally, we must compare the facility’s entrance skin exposure for chest, abdomen and LS spine examinations to that obtained during the Annual Medical Physicist’s Radiographic QC Survey. These units are measured in milli Roentgen (mR).

Calculation

The Entrance Skin Exposure (ESE) can be calculated by using the following equation.

ESE Formula

where I2 is the calculated ESE

I1 / I2 = [mAs1 / mAs2] x [(kVp1)^2 / (kVp2)^2]

Real world Example:

A certain technique calls for 85 kVp/40 mAs and results in 120 mR. What is the expected ESE if the kVp is increased to 100 kVp and the mAs is increased to 50 mAs?

This formula is a little different. But we will solve it the same way. First plug in the values.

120mR / I2 = [40 mAs / 50 mAs] x [(85 kVp)^2 / (100 kVp)^2]

Cross multiply.

I2 = [120mR)(50mAs)(100 kVp]^2 / (40 mAs) (85kVp)^2

Solve for the variable.

I2= 208mR

Rad Procedure

Radiograpghic ESE test frequency, technique factors, and procedures.

Test Frequency

Semi-Annually

SID

40”

Technique Factors

32 mAs, no filtration (open air only)

Test Tools

A X-ray Quality Assurance meter (e.g. RTIs Piranha or Barracuda)

Procedures

1. Place a QA meter on top of table.

2. Set the SID to 40” and lock in place.

3. Take a series of four shots without any filtration at 60 kVp, 80 kVp, 100 kVp, and 120 kVp while the 32 mAs always stays the same.

4. Measure each kVp exposure in milliRoentgen (mR) and record.

Fluoro Procedure

Radiograpghic ESE test frequency, technique factors, and procedures.

Test Frequency

Semi-Annually

SID

19”

Technique Factors

32 mAs, no filtration (open air only)

Test Tools

A X-ray Quality Assurance meter (e.g. RTIs Piranha or Barracuda)

Procedures

1. Place a QA meter on top of table.

2. Set the SID to 19” and lock in place.

3. Take a series of four shots without any filtration at 60 kVp, 80 kVp, 100 kVp, and 120 kVp while the 32 mAs always stays the same.

4. Measure each kVp exposure in milliRoentgen (mR) and record.

References


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