2. As kVp Increases, There is a higher chance that the person who is holding the patient during the procedure will
ABSORB more
SCATTER RADIATION.
So apply proper
RADIATION PROTECTION
4. Inverse Square Law
- As the law states: "X-ray intensity varies inversely with the square of the distance from the x-ray tube
2. Anode Heel Effect
Line Focus Principle
- It is a design incorporated into x-ray tube to provide large area for heating while maintaining a small focal spot
- Line Focus Principle is simply the ANGLE of the Anode
- This Provides a more smaller Effective focal spot than the Actual area of interaction or the Actual focal spot.
- As the distance increases, the Intensity that the IR receives also decreases
- Due to the angle of the anode, x-rays that are emitted in the side of the anode must traverse a greater thickness of target material than the cathode side.
- The smaller the Anode Angle, the greater is the Heel Effect
So for x-ray Procedures like:
Where should be the Anode side Located?
Key to Producing Quality Radiographs by using Proper Radiographic Technique
1. 15% kVp Rule
3. Body Habitus and Different Pathological Diseases Technical Factor Adjustment
- But there is also a rule in which if you need to change the Density slightly you will use the 5 percent rule.
- This rule states that increasing the kVp by 5% will result in increase of Density by 30%.
- As we all know there are four different body habitus which are:
- As we said earlier kVp controls Contrast, but it also affects Density.
- As the rule states If the Density of the radiograph is to be increased using kVp, an increase in 15% of kVp results in doubling the mAs.
Note:
If there is technique for changing Density while using kVp. There is a technique also available for the controlling factor of Density which is mAs.
To change the Density on the film using mAs, A change of approximately 30% on mAs is required to produce a visible change on the radiograph.
- The Sthenic Body type is the basis for all Technique Charts, because they are the normal types of patients.
- So when encountering Hyposthenic patients decrease the factor a little bit.
- While for Asthenic patients or the Geriatric ones, Further decrease the factor based on hyposthenic patients.
- While For the Big Ones (Hypersthenic) Increase the factor which will be needed to produce the quality radiograph.
Remember:
Always use the Principle of ALARA while doing Radiographic Procedures
Different Pathologies
There are two types of Pathology:
1. Destructive Pathology - is a type of pathology that causes the tissue to be more radiolucent. DECREASE FACTOR
2. Constructive Pathology - another kind of pathology that causes the tissue to be more radiopaque. INCREASE FACTOR
- Mastering correct usage of technical factor is a must.
3. Distance (SID & OID)
Technique Basic Conversion and Relationship
3.1 SID (Source-to-Image Distance)
- As SID Increases, Detail Increases
- As SID Increases, Exposure Factor must be Increased
Direct Square Law
- To know how much kVp should be used, use CALIPERS
"X-ray Quantity is inversely proportional to the square of the distance from the source"
- From that statement, as a RT we need to adjust mAs to compensate for the change in Distance
Direct Square Law
3.2 OID (Object-to-Image Distance)
- As OID Increases, Detail Decreases
- As OID Increases, Less Scattered Radiation wil received by the IR.
Thank you!
- For every 1 cm of thickness added to the part to be x-rayed, 2 kVp must be added to the original factor
- Different Patients need Different Technical Factors
- But Today's Digital age, the life of an RT is much easier due to the rise of AEC's. Manual Factoring has almost declined in usage making patient more exposed to radiation
- But as a RT we should know how to adjust Technical Factors manually and not to depend only on AEC.
- mAs are variable depending on the examination.
- Assesing the Patient size and Current Condition should be the first step before starting the procedure.
- This will help lessen repeat x-ray and protect the patient from excessive radiation
- Because if you already know the condition of the patient, you can now calculate the technique factor that you should use
Influencing Factors in the Production of Image
- Exposure Factors are key elements in producing a radiograph
Applying the Concept of Exposure Factors, Technical Conversions, Assessment of the Patient Condition and Proper Positioning can limit Repeat Exposure.
No Repeats = Less Work
- These Exposure Factors are kVp, mA, Exposure Time (s), and SID
1. kVp
Formula For kVp and X-ray Quantity
- Every RT students should be wary on how to use them wisely.
"If kVp were doubled, the xray intensity will increase by a factor of four"
- Thus kVp and X-ray Quantity has a Direct Relationship
- kVp controls Contrast
- They have an Inverse Relationship
- kVp controls Radiation Quality and affects Radiation Quantity
- Increase in kVp, Contrast Decreases
- kVp Controls the Scale of Contrast
Other effects of kVp
Effects of kVp on Contrast
1. As kVp Increases, LESS RADIATION will be received by the patient
1. As kVp Increases, More Scatter radiation will be produced, thus Reducing Contrast
2. As kVp Increases, More X-rays will penetrate the part then will come contact with the IR, thus Reducing Contrast
Introduction
2. mAs
- mAs controls Density
- They have a Direct Relationship
- Increase in mAs, Density Increases
- mAs controls Radiation Quantity
Formula for mAs and X-ray Quantity
"If mAs is doubled the number of elecrons striking the tube target is doubled, therefore number of x-rays emitted are doubled
- Thus X-ray Quantity is directly proportional to mAs.
Other Effects of mAs
Effects of mAs on Density
1. As mAs Increases, Patient Dose also INCREASES.
1. As mAs Increases, More electrons will be available for the production of X-ray
2. As mAs Increases, More Heat is produced in the Anode.
2. As mAs Increases, More x-rays will be produced and can interact with the IR.
In Producing a Quality Radiograph, RT's or RT Students Need to Apply Knowledge in Radiographic Positioning and in Radiographic Technique
Reginald H. Esteban, RRT