(5*) Technique Charts / Tube Rating Charts / Radiographic Grids

(1) #2 because the first one has such thick lead strips that it will absorb more of the exit beam than you want it to. Because they are so thick it will cast an image of the grid onto the IR (2) #1 More lead to absorb scatter from hitting the IR (3)#1 Bc you need more dose to get through the lead

Answer these 3 questions

The grid with the lower grid frequency because the thicker lead strips will clean up more scatter

Comparing two grids of the same GR but different frequency, which would provide the best efficiency?

The grid with the higher grid frequency because the lead strips are thinner and won't show up on the image

Comparing two grids of the same GR but different frequency, which would provide the best visibility of detail?

The grid with the lower grid frequency because the thicker lead strips require more x-ray production to get through the large amount of lead

Comparing two grids of the same GR but different frequency, which would provide the highest dose?

- Lead strips are canted (Angled) to match the divergent CR - CENTER strips are perpendicular to the IR and as you get to the periphery, they angle more - Better set up for lower SID

Define Focused Linear Grid

The number of lead strips per inch

Define Grid Frequency

Lead strips are perpendicular to the IR and parallel to each other

Define Parallel Linear Grids

- There will be loss of RE on the LATERAL EDGES of the image - The closer you are, the more you open up your collimation, the x-rays diverge more and they don't line up as well anymore

Describe Parallel Linear Grid Cutoff

- You would find the lowest or most common used GR, which would be 8:1 in this problem - You would then calculate the other two problems by plugging the number in to new mAs = old mAs * (new GCF/old GCF) - Once you find all the new mAs', your highest one would give you the greatest receptor exposure

Describe how you would solve this:

- mA, (s), and kVp are plotted on the chart - If the technique falls on or below a curve, it is safe

Describe the Interpretation of the Radiographic Rating chart.

The greater the angle of scatter, the more likely it is to be absorbed.

Describe the angle of incident scatter when it comes to using a grid

- Upside-down Grid Cutoff: 6:1 Cross - This grid was made with two focused, linear grids turned 90 degrees apart and placed on top of each other. Notice how there is a loss of receptor exposure on all four edges but not in the middle

Describe this kind of cutoff and what is actually going on here

(1) If you use a certain technique and for some reason it is an unsafe, you can use the reciprocity law to possible get you an exposure that is safe.

Determine what effect the Reciprocity Law and the 15% Rule would have on Radiographic Rating Charts

- 103 to 200 lines per inch - 140

Digital IR's are more sensitive. What range do they require for GF and what is the average?

Raise

Do grids raise or lower patient dose?

YES

Does the 15% rule have an affect on HU production?

- Flip the time numbers sequence .... So start with 8 and work your way down to one - 500x100x1.5=75,000 - After finding the HU, follow that line over to where it intersects to the cooling line and go down to see how much time it takes to cool down. The answer is 3.1seconds

Explain what to do first with the Anode Cooling Chart. And the answer the questions below the chart

The one with fewer lead strips because the strips are thicker (have more lead) - more lead leads to better scatter clean up

For grids with equal GRs, which will be more efficient at removing scatter by virtue of a higher lead content?

- Between 50 and 200 lines per inch - 85-103 lines per inch

Grid frequency varies between how many lead strips per inch? What is the most common range?

mA (x) Time (x) kVp (x) 1.45

HU calculations: High Frequency

mA (x) Time (x) kVp

HU calculations: Single phase

mA (x) Time (x) kVp (x) 1.41

HU calculations: Three Phase 12-Pulse

mA (x) Time (x) kVp (x) 1.35

HU calculations: Three Phase 6-Pulse

By finding patterns and removing them.

How do digital grid suppression algorithms prevent the moire effect from impacting image quality?

Occurs if two focused linear grids are placed on top of one another with the lead strips running in the same direction

How does the Moire effect occur?

They are not related and are independent of each other

How is GR and the thickness of the lead strips related?

Two linear grids placed on top of one another and rotated 90 degrees

How is a crosshatch (crossed) grids constructed?

If the tube is not properly tranverse centered

How is off-center grid cut off caused?

Severe loss of receptor exposure on the lateral edges of the image

How is receptor exposure affected with Upside-down Grid Cutoff?

1.5 million

How many Heat units can a Housing Cooling Chart go to?

There is greater clean-up

If you have a higher grid ratio but EVERYTHING OTHER PART OF GRID CONSTRUCTION REMAINS CONSTANT, what happens to scatter?

It would be going the opposite direction so you would lose the image on the periphery

If you took a focused linear grid and turned it upside down, what would it look like?

It would look like nothing bc it would still be linear or parallel. It doesn't matter if it was upside down.

If you took a parallel linear grid and turned it upside down, what would it look like?

No, because of the inverse square law. The distance gets shorter but you are cutting your mAs in order to keep your pt dose the same. They will both be the same amount of dose.

If you're doing an abdomen series, which involves a chest at 72" and then your abdomen/KUB at 40", Your mAs will go down when you bring in the SID due to inverse square law. If you bring into 60" instead of 40", you will still bring your mAs down but not as much. Is the patient getting a higher dose when it is at a closer distance?

Higher GRs require more accuracy in their use and result in a higher patient dose

In what way do higher GRs affect accuracy and patient dose?

Yes bc the limiting factor for flouro is the tube housing.

Is it possible to damage the tube housing before the target? (Test question)

(1) Transfer (2) Photoelectric (3) Compton (4) X-ray left patient at a greater angle so it is absorbed by the grid

Label the different types of x-rays

(1) kVp (2) Time (s) (3) mA -YES

Label the parts to the Radiographic Rating chart and the answer the question at the bottom

(1) HU stored in housing (2) With a circulator (3) Without a circulator (4) Cooling time

Label the the parts of this Housing Cooling Chart

Occurs when the focal range has been breached

Off-focus Grid Cut off (aka Off-distance Grid Cutoff) occurs when?

Along the lateral edges of the image

Off-focus Grid Cutoff has loss of receptor exposure where on the image?

Warmed up

Should the tube be cool or warmed up when using radiographic rating chart?

(1) Linear -Parallel -Focused (2) Crosshatch

Types of Grids

(1) How much total heat is produced during an exposure (2) How long you must wait for the tube to cool

What 2 things does the Anode cooling chart is used to determine?

(1) mA (2) Time (3) kVp

What 3 technical factors are plotted on the Radiographic Rating chart?

(1) More primary beam absorption - because of more lead content (2) Less visibility of detail - the grid is in the way when creating the image (3) Higher patient dose - because higher x-ray production is needed to go through the grid

What 3 things will Grids with fewer but thicker lead strips result in?

No impact

What affect does Reciprocity Law have on HU production?

(1) Doing a portable and the IR is not flat under the patient (2) Tube is not exactly angled right

What are 2 causes of Off-level grid cut off?

(1) Focal Spot Size (2) Anode Rotation Speed (3) The Type of Rectification

What are 3 factors to consider whether a single exposure is safe or unsafe?

(1) To standardize exposure variables (2) Reduce repeats (3) Decrease patient exposure

What are 3 reasons to why is it important to use technique charts?

HU in millions=Housing

What are Housing Cooling charts measured in?

(1) A standard technique is determined by doubling the patient thickness in cm and adding 40 (2) Two kVp are then added or subtracted for each change in patient thickness

What are the 2 steps in creating fixed mAs and Variable kVp charts?

(1) Most widely employed (2) There is an optimum kVp for all exams (3) Provides consistent penetration

What are the 3 attributes of fixed kVp, Variable mAs chart?

(1) Radiographic Rating Chart (2) Anode Cooling Chart (3) Fluoroscopy Anode Cooling Chart (4) Housing Cooling Chart

What are the 4 types of Rating Charts?

(1) CR vs. DR (2) Grid vs. Non Grid (3) SID (4) AEC Factors (5) Patient Size (6) Focal Spot

What are the 6 factors to consider in using technique charts?

- To maintain receptor exposure, use the following formula new mAs = old mAs * (new GCF/old GCF)

What are the Grid-to-Grid Adjustments?

1 2 3 4 5 6

What are the grid conversion factors (GCF)? (1) Non Grid = (2) 5:1 = (3) 6:1 = (4) 8:1 or 10:1 = (5) 12:1 = (6) 16:1 =

Linear - They run in the same direction

What are the most common type of grids and what direction do they go?

Off-Center or Off-Level (Tube angle or IR tilted)

What are the types of cut offs that lose the entire image across the IR?

The tube can not be angled

What can not be done with the tube with a crosshatch grid?

Fans

What do Housing Cooling Charts use to cool down?

- HU/sec=Fluoroscopy - Multiply mA, kVp and time.... No specific time... Time is however long you hold the pedal down and mA will be very low

What do we use to measure on the Fluoroscopy Anode Cooling Chart? How do we do the calculation to get that number?

Alternating lead strips and interspace material (Usually aluminum)

What does the construction of a grid consist of?

103 lines per inch or more

What grid frequency will alleviate the moire effect?

If the kVp raises too high then the x-ray will penetrate through the iodine which has a low Z#

What happens when using fixed mAs, variable kVp chart during iodine exams?

The height of the lead strips divided by the distance between them. GR = h/D

What is Grid Ratio?

Interventional Radiography

What is an application for a crosshatch grid?

Off-distance Grid Cutoff

What is another name for an Off-focus Grid Cutoff?

The range of SIDs that works best with the grid

What is focal range or grid radius?

Target - Anode - Dielectric Oil - Tube Housing - Air

What is the flow of heat dissipation in the tube

Infinity

What is the focal range for parallel linear grids?

Target

What is the limiting factor for exposures <1 second?

Anode Disk

What is the limiting factor for exposures >1 second?

Tube housing

What is the limiting factor for fluoroscopy exposures?

Amount of lead

What is the most important aspect of a grid?

Lead content

What is the most important factor to consider in grids that is often overlooked?

Fixed kVp, Variable mAs chart

What is the other technique chart besides fixed mAs, variable kVp chart?

Removes secondary and scatter in both directions - VERY EFFICIENT at absorbing scatter

What is the purpose of a crosshatch grid?

Determines whether a SINGLE exposure is safe or unsafe

What is the radiographic rating chart used for?

Off-Center

What kind of cut off is this?

Because the IR with grid can be so heavy, it may cause some sort of tilt. It is best to use a decub grid because the lines run up and down instead of side to side to compensate for that possible tilt.

What kind of grid is best used for a this type of cross table and why?

Loss of receptor exposure across the ENTIRE IMAGE (i.e. even loss of receptor exposure across the IR)

What kind of receptor exposure loss is experienced in off-center grid cutoff?

Reverse the numbers at the bottom

What must you to ALL cooling charts before calculating and numbers?

New mAs = old mAs (new GCF/old GCF) New mAs = 32 x 5/3 New mAs = 53.4

What new mAs would be required to maintain the original receptor exposure if you switched from a 6:1 GR to a 12:1 GR and the original mAs was 32?

Lead content

What serves as an indicator of grid performance?

Grid Suppression software

What software gets rid of these lines?

Off-focus Cutoff - The distance is off. The Focal range is given at 34"-44" but the distance was actually set at 30"

What type of cutoff caused this image?

(1) Upside-down Grid Cutoff: 6.1 GR (2) Upside-down Grid Cutoff: 15:1 GR - This shows how necessary it is to be more accurate with a higher GR

What types of cutoff?

Heat Units (HU) - not BTU

What units are used to measure anode heat?

Fixed mAs, Variable kVp Charts

What was the first technique chart created?

When stationary grids are employed

When can the Moire Effect occur with digital imaging systems?

When the focal range has been breached

When does Off-focus Grid Cutoff occur?

When the grid is turned upside down but rarely occurs due to modern grid cap construction

When does Upside-down Grid Cutoff occur?

Grids should be used on body parts > 10 cm and for any kVp > 70

When should grids be used?

You lose the optimum kVp - No Consistency w/ scale of contrast

When you use fixed mAs, variable kVp chart what happens to optimum kVp?

6:1 crossed grid

Which will remove more scatter: A 6:1 crossed grid or 12:1 linear grid?

There will be less grid cut off due to the focal range being infinity - the further you get away, the better - Because of the distance the primary beam can slip in

Why do parallel linear grids work best with a long SID?