Radiology Inverse Square Law Flashcards
19 Questions
101 Views

Choose a study mode

Play Quiz
Study Flashcards
Spaced Repetition
Chat to Lesson

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What is the inverse square law?

The intensity of the x-ray beam varies inversely with the square of the source to film distance.

What will be influenced if the source-to-film distance (SFD) is changed?

The density of the radiographs.

What are the two rules of thumb to maintain the original density when a change in SFD occurs?

  1. If SFD is doubled, the exposure time should be multiplied by 4. 2. If SFD is halved, exposure is divided by 4.

If an 8 inch PID with 15 mA, 80 kVp, and 0.01 impulses is changed to a 16 inch PID with the same mA and kVp, what would the impulses be?

<p>Double the impulses; 0.01 x 4 = 0.04 impulses.</p> Signup and view all the answers

If a 16 inch PID with 15 mA, 90 kVp, and 20 impulses is changed to an 8 inch PID, what would the impulses be?

<p>5 impulses; 20 / 4 = 5.</p> Signup and view all the answers

What does mA control?

<p>The quantity of number of x-rays produced.</p> Signup and view all the answers

What is the rule of thumb for changes in mA to maintain density?

<ol> <li>An increase of 5 mA will increase the number of x-rays produced, divide the time by 2. 2. A decrease in 5 mA will decrease the number of x-rays, multiply the time by 2.</li> </ol> Signup and view all the answers

If 5 mA at 0.30 seconds is increased to 10 mA, what is the new time?

<p>0.15 seconds; 0.30 / 2 = 0.15.</p> Signup and view all the answers

If 10 mA at 0.20 seconds is decreased to 5 mA, what is the new time?

<p>0.40 seconds; 0.20 x 2 = 0.40.</p> Signup and view all the answers

What does kVp control?

<p>Quality or penetrating power of x-rays; it is a minor factor in controlling quantity of x-rays.</p> Signup and view all the answers

A change in kVp will alter what?

<p>Density or quantity of x-rays produced.</p> Signup and view all the answers

What are the rules of thumb for kVp?

<ol> <li>If kVp is increased by 15 kVp, it will increase the number of x-rays; to maintain density, divide time by 2. 2. If kVp is decreased by 15, it will decrease the number of x-rays; multiply time by 2.</li> </ol> Signup and view all the answers

If 60 kVp at 0.50 seconds is increased to 75 kVp, what is the new time?

<p>0.25 seconds; 0.50 / 2 = 0.25.</p> Signup and view all the answers

If 85 kVp at 0.50 seconds is decreased to 70 kVp, what is the new time?

<p>0.30 seconds; 0.15 x 2 = 0.30.</p> Signup and view all the answers

A good radiograph was made using a source-to-film distance of 16 inches and an exposure of 20 seconds. If the source-to-film distance is decreased to 8 inches, what would the correct exposure time be?

<p>5 seconds; 20 / 4 = 5 seconds.</p> Signup and view all the answers

A radiograph is exposed using 85 kVp at 0.15 seconds. The kVp is decreased to 70 kVp. What will the new time be?

<p>0.30 seconds; 0.15 x 2 = 0.30 seconds.</p> Signup and view all the answers

If a satisfactory radiograph is produced using a source-to-film distance of 8 inches and an exposure time of 1 second, what would the correct exposure time for a source-to-film distance of 16 inches be?

<p>4 seconds; 1 x 4 = 4 seconds.</p> Signup and view all the answers

A diagnostic film produced using 90 kVp and 0.25 seconds. What exposure time is needed to produce the same film at 75 kVp?

<p>0.50 seconds; 0.25 x 2 = 0.50.</p> Signup and view all the answers

If a diagnostic radiograph is produced using 5 mA at 0.30 seconds, what exposure time is needed to produce the same film using 15 mA?

<p>0.075 seconds; for each increase of 5 mA, the time must be divided by 2, so 0.30 / 4 = 0.075.</p> Signup and view all the answers

Flashcards

Inverse Square Law

X-ray beam intensity decreases as distance from the source increases, inversely proportional to the square of the distance.

SFD Effect on Radiograph Density

Changing the source-to-film distance (SFD) directly affects the radiograph's darkness (density).

Doubling SFD

Doubling the source-to-film distance requires quadrupling the exposure time to maintain density.

Halving SFD

Halving the source-to-film distance reduces the exposure time to one-fourth of the original.

Signup and view all the flashcards

8 inch to 16 inch PID Change

Changing from an 8 inch to 16 inch PID doubles the impulses needed (e.g., 0.01 becomes 0.04) to maintain density.

Signup and view all the flashcards

16 inch to 8 inch PID Change

Changing from a 16 inch to 8 inch PID reduces the impulses to one-fourth of the original (e.g., 20 impulses becomes 5) to maintain density.

Signup and view all the flashcards

Milliamperes (mA)

mA controls the quantity (number) of x-rays produced during exposure.

Signup and view all the flashcards

5 mA Increase

Increasing mA by 5 halves the exposure time to maintain the same density.

Signup and view all the flashcards

5 mA Decrease

Decreasing mA by 5 doubles the exposure time to maintain the same density.

Signup and view all the flashcards

kVp Effect

kVp affects the quality (penetrating power) and slightly the quantity of x-rays.

Signup and view all the flashcards

kVp Increase

Increasing kVp by 15 halves the exposure time to maintain the same density.

Signup and view all the flashcards

kVp Decrease

Decreasing kVp by 15 doubles the exposure time to maintain the same density.

Signup and view all the flashcards

16 inch to 8 inch SFD Time Change

Reducing SFD from 16 inches to 8 inches requires reducing the exposure time to one-fourth of the original.

Signup and view all the flashcards

8 inch to 16 inch SFD Time Change

Increasing SFD from 8 inches to 16 inches requires quadrupling the exposure time to get same density.

Signup and view all the flashcards

kVp 85 to 70 Time Change

Decreasing kVp from 85 to 70 requires doubling the exposure time.

Signup and view all the flashcards

mA 5 to 15 Time Change

Increasing mA from 5 to 15 requires reducing the exposure time to one-fourth of the original.

Signup and view all the flashcards

Density

Radiographic darkness.

Signup and view all the flashcards

Study Notes

Inverse Square Law

  • The intensity of the x-ray beam decreases as the distance from the source increases, specifically varying inversely with the square of the source-to-film distance (SFD).

Effects of Changing SFD

  • A change in SFD will directly influence the density of the radiographs produced.

Rules of Thumb for Changing SFD

  • Doubling the SFD requires an increase in exposure time by a factor of four.
  • Halving the SFD allows for a decrease in exposure time to one-fourth of the original duration.

Impulses Adjustment with SFD Change

  • When changing from an 8 inch PID to a 16 inch PID while maintaining the same mA and kVp, the impulses needed will double (e.g., 0.01 becomes 0.04).
  • Conversely, changing from a 16 inch PID to an 8 inch PID will require the impulses to be reduced to a quarter (e.g., 20 impulses becomes 5).

Milliamperes (mA) Control

  • mA controls the quantity or number of x-rays produced during exposure.

mA Adjustment Rules

  • An increase of 5 mA necessitates halving the exposure time to maintain density.
  • A decrease of 5 mA requires doubling the exposure time to preserve image quality.

Time Adjustment with mA Changes

  • If mA is increased from 5 to 10, the time is halved from 0.30 seconds to 0.15 seconds.
  • If mA decreases from 10 to 5, the time doubles from 0.20 seconds to 0.40 seconds.

Kilovoltage Peak (kVp) Control

  • kVp influences the quality and penetrating power of x-rays, playing a minor role in the quantity produced.

Density Adjustment with kVp Changes

  • A modification in kVp alters both the density and the quantity of x-rays generated.

kVp Adjustment Rules

  • Increasing kVp by 15 requires halving the exposure time to maintain density.
  • Decreasing kVp by 15 necessitates doubling the exposure time to achieve the same effect.

Time Adjustment with kVp Changes

  • If kVp increases from 60 to 75, exposure time is shortened from 0.50 seconds to 0.25 seconds.
  • Reducing kVp from 85 to 70 requires time to be adjusted from 0.15 seconds to 0.30 seconds.

SFD and Exposure Time Relationship

  • A satisfactory radiograph exposed at 16 inches for 20 seconds will only need 5 seconds when the SFD is reduced to 8 inches.
  • For an SFD of 16 inches, if starting from an exposure of 1 second at 8 inches, the time required becomes 4 seconds.

Final Time Adjustment Scenarios

  • Reducing kVp from 85 to 70 while maintaining exposure time requires multiplying the initial time (0.15 seconds) by 2, resulting in 0.30 seconds for the new exposure duration.
  • Producing a diagnostic radiograph with increased mA to 15 from 5 mA at 0.30 seconds requires dividing the time by 4, yielding 0.075 seconds for proper density maintenance.

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Quiz Team

Description

Study the fundamentals of the inverse square law in radiology with these flashcards. Explore key concepts such as the relationship between x-ray intensity and source-to-film distance, as well as practical rules of thumb for maintaining radiographic density. Perfect for radiology students and professionals looking to reinforce their knowledge.

More Like This

Use Quizgecko on...
Browser
Open
Browser
Browser