Rad Physics Chapter 10: Filtration

Filtration in radiology refers to the technique used to remove low-energy x-ray photons that contribute to image degradation, ensuring clearer and higher quality images by selectively absorbing them with materials like aluminum.

Filtration works by selectively removing low-energy photons from the x-ray beam, thus improving the quality of the emitted spectrum by reducing the number of less useful photons.

Filtration in radiography is known as 'hardening' of the beam because it selectively removes low energy ('soft') photons, increasing the average energy of the beam.

Soft tissue penetration requires the energy range of 30-40 keV to effectively penetrate the tissue. Lower energy levels may not be sufficient to penetrate the soft tissue, while higher energy levels can result in excessive radiation exposure.

Filtration is necessary in x-ray imaging to remove low energy photons which do not contribute to image quality but only increase patient radiation dose.

Filtration is commonly measured in terms of the amount of aluminum or its equivalency used, as aluminum is a well-known standard filtering material.

The correct answer explains the concept of Half-Value Layer in terms of radiation physics.

The correct answer includes the specific types of filtration used in various industries to remove impurities from liquids or gases.

Inherent Filtration refers to the natural filtration that occurs due to the materials present in the X-ray tube and its housing, such as glass envelope, dielectric oil bath, and glass window.

HVL testing is crucial in determining the changes in filtration over time which directly affects the tube efficiency and image quality in medical imaging systems.

Added filtration in radiography refers to any additional filtration that is placed outside the x-ray tube and before the image receptor. This added filtration helps in removing low-energy photons, resulting in a higher quality image with better contrast and reduced scatter radiation.

Added filtration in X-ray machines is essential to remove unnecessary radiation and reduce patient exposure. Examples of added filtration include using sheets of aluminum between the x-ray tube housing and the collimator, and using collimators (1mm al/eq) to block unnecessary radiation.

Compound filtration in medical imaging refers to filters that use two or more materials; where each layer absorbs characteristic photons created from the previous layer. This is why it is layered from highest atomic number to lower atomic number (closest to the patient).

Compound filters used in radiology include lead, copper (#29), and aluminum (#13). Aluminum is particularly effective due to the absorption of low energy photons. Steel, brass, and nickel are not typically used as compound filters in this context.

Compensation Filtration is specifically used to address the issue of parts with uneven tissue thickness or densities, helping to produce more uniform and accurate radiographic images.

Compensating filters are used in radiography to even out the exposure when imaging parts of the body that have varying tissue densities. Each type of filter is designed to compensate for specific anatomical characteristics, hence their common usage in particular X-ray procedures.

Total Filtration is the combination of both inherent and added filtration levels, excluding compound or compensating filters.

Total filtration involves specific components such as a glass envelope, window, dielectric oil, and sheets of aluminum with a silver backing on collimator mirrors to achieve the desired filtration results.

Filtration in X-ray tubes is important as it removes low energy photons which can contribute to image noise. However, it also removes some higher energy photons which leads to a decrease in radiographic density. This decrease in density can be compensated for by increasing the kilovoltage peak (KVP) setting during the X-ray exposure process.

When the exposure needs to be increased to maintain the same exposure factors, increasing factors with more filtration results in a greater decrease in overall exposure to the patient due to the greater percentage of low energy photons being absorbed.