Radiographic Noise Types and Definitions

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Questions and Answers

What is considered a feature of a good quality radiograph?

  • High contrast and clarity (correct)
  • Low exposure time regardless of image quality
  • Overexposure leading to increased brightness
  • Complexity of the imaging process

Which factor does NOT affect definition in radiographic images?

  • Patient size (correct)
  • Focal spot size
  • Film speed
  • Image receptor distance

What does the term 'Line Focus Principle' refer to in radiography?

  • The method to optimize spatial resolution
  • The alignment of the x-ray beam with the patient
  • The technique used to minimize image noise
  • The use of angled anodes to improve detail (correct)

Which of the following is an application where unsharpness is intentionally utilized?

<p>In artistic radiographic images (D)</p> Signup and view all the answers

Which image quality measurement does not directly relate to radiographic noise?

<p>Spatial frequency response (D)</p> Signup and view all the answers

What happens to the size of the effective focal spot (EFS) when the angle of the anode is decreased?

<p>The EFS size increases. (D)</p> Signup and view all the answers

How does an increase in the speed of anode rotation affect the actual focal spot size?

<p>It allows the use of a smaller actual focal spot. (B)</p> Signup and view all the answers

Which factor is NOT directly proportional to the effective focal spot (EFS) size according to the summarized factors?

<p>Voltage of the focusing cup (A)</p> Signup and view all the answers

When attempting to decrease the unsharpness (Ug) due to object image distance (OID), which statement is true?

<p>Decreasing OID decreases Ug. (A)</p> Signup and view all the answers

What is the consequence of maintaining a heavy thermal load on the target while using a small focal spot?

<p>It restricts field coverage. (A)</p> Signup and view all the answers

What causes absorption unsharpness (Ua) in imaging?

<p>The oval shape of certain anatomic organs (D)</p> Signup and view all the answers

Which factor is considered a primary contributor to total unsharpness (Ut)?

<p>Motion unsharpness (Um) (B)</p> Signup and view all the answers

What is the effect of increasing the source-to-image distance (SID) on image unsharpness?

<p>Decreases motion unsharpness (Um) (D)</p> Signup and view all the answers

Which method is used for objective measurement of image sharpness?

<p>Line Spread Function (LSF) (B)</p> Signup and view all the answers

How does attempting to reduce one type of blur in imaging affect other types of blur?

<p>It can cause an increase in different types of blur (B)</p> Signup and view all the answers

What is the primary function of a Charge Couple Device (CCD) in imaging systems?

<p>To convert light signals into electrical signals (C)</p> Signup and view all the answers

Which characteristic of CCDs contributes to their high x-ray capture efficiency?

<p>Their highly sensitive nature to light (D)</p> Signup and view all the answers

What is a significant advantage of using Amorphous Selenium (a-Se) in imaging?

<p>It offers better spatial resolution than indirect systems (D)</p> Signup and view all the answers

How does the fill factor affect radiation requirements in imaging systems?

<p>A higher fill factor reduces necessary radiation (A)</p> Signup and view all the answers

What limits the spatial resolution in a digital imaging system?

<p>The size of the detector element (DEL) (B)</p> Signup and view all the answers

What is a major advantage of Direct Radiography (DR) compared to Computed Radiography (CR)?

<p>Greater efficiency in time, space, and personnel (C)</p> Signup and view all the answers

Which algorithm is used by Kodak for image processing?

<p>Enhanced Visualization Processing (D)</p> Signup and view all the answers

What does the Fill Factor indicate in Digital Radiography?

<p>Percentage of the DEL surface sensitive to light (B)</p> Signup and view all the answers

What is a characteristic of Cesium Iodide (CsI) crystals in Digital Radiography?

<p>They are needle-like in shape to improve spatial resolution. (B)</p> Signup and view all the answers

What is the primary function of the Thin Film Transistor (TFT) in the imaging system?

<p>To store energy as an electrostatic field (D)</p> Signup and view all the answers

What are the two main imaging systems in Digital Radiography?

<p>Direct Radiography and Computed Radiography (A)</p> Signup and view all the answers

Which factor directly affects the sensitivity and spatial resolution of a digital imaging system?

<p>Detector Quantum Efficiency (DQE) (A)</p> Signup and view all the answers

What is a characteristic of the digital image histogram in digital radiography?

<p>It uses modeling histograms for body part projections. (B)</p> Signup and view all the answers

What advantage does a wide dynamic range provide in digital radiography?

<p>It allows recording of very low radiation exposure levels. (C)</p> Signup and view all the answers

What is an important benefit of eliminating the use of cassettes in digital radiography systems?

<p>It significantly improves efficiency and reduces noise. (B)</p> Signup and view all the answers

Which application is explicitly not supported by Computed Radiography (CR)?

<p>Angiography (B)</p> Signup and view all the answers

What is the purpose of using aluminum in the construction of a CR cassette?

<p>To absorb backscatter radiation (D)</p> Signup and view all the answers

What feature is critical for minimizing artifacts when using stationary grids in CR?

<p>Grid latitude of 103 lines/inch or higher (D)</p> Signup and view all the answers

What characteristic of Photostimulable Storage Phosphor (PSP) plates makes them sensitive to image artifacts?

<p>Sensitivity to ambient light after exposure (A)</p> Signup and view all the answers

How is patient identification performed in the AGFA CR system?

<p>Via a no-touch built-in antenna card (B)</p> Signup and view all the answers

Which component of the CR system is responsible for converting the latent image into a visible image?

<p>CR reader (A)</p> Signup and view all the answers

What is the primary difference between direct and indirect digital systems in radiography?

<p>Indirect systems convert x-rays to light, while direct systems convert x-rays to electric signals. (D)</p> Signup and view all the answers

What layer of the CR plate is primarily responsible for storing the latent image?

<p>Phosphor layer (C)</p> Signup and view all the answers

Which feature of a CR plate is essential for its ability to be reused multiple times?

<p>Efficient radiation storage properties (D)</p> Signup and view all the answers

What does the exposure index value in CR indicate?

<p>The amount of radiation used during the exposure (B)</p> Signup and view all the answers

What percentage of energy is stored in the imaging plate after x-ray exposure?

<p>50% (B)</p> Signup and view all the answers

What is the role of Europium in the phosphor crystals?

<p>It enhances the storage property of the crystal. (A)</p> Signup and view all the answers

What occurs to the latent image when it is not processed immediately after exposure?

<p>It degrades within a short period. (D)</p> Signup and view all the answers

Which factor affects the release of trapped electrons during the processing of a CR plate?

<p>The intensity of the external stimulation source. (C)</p> Signup and view all the answers

What is the recommended timeframe for processing an exposed CR plate to preserve the integrity of the image?

<p>Within the first two hours. (A)</p> Signup and view all the answers

What must be true for a government institution to use an individual's personal information?

<p>The use must align with the original purpose for which it was obtained. (B)</p> Signup and view all the answers

Who has the right to access personal information under Section 12?

<p>Every Canadian citizen or permanent resident. (D)</p> Signup and view all the answers

What is the timeframe a government institution has to respond to a request for personal information access?

<p>30 days. (D)</p> Signup and view all the answers

What does Chapter a-2.1 primarily address?

<p>Guidelines for protecting patient health information. (B)</p> Signup and view all the answers

What must an individual do to access personal information about themselves from a government institution?

<p>Complete a written request with specific details. (C)</p> Signup and view all the answers

What is the main function of pre-fetching in a hospital PACS system?

<p>To automatically download previous exams from the DSQ. (C)</p> Signup and view all the answers

Which responsibility is NOT assigned to the system manager (PACS Admin)?

<p>Develop access policies for system integrity. (D)</p> Signup and view all the answers

What is a primary duty of the authorities regarding system data?

<p>Update system access policies to ensure data integrity. (A)</p> Signup and view all the answers

Which of the following is a correct procedure for handling patient data by the system manager?

<p>Only access confidential data necessary for work. (A)</p> Signup and view all the answers

What should the system manager do to ensure the security of confidential information?

<p>Implement rules for password complexity and change. (C)</p> Signup and view all the answers

What does Section 4 of the Privacy Act state regarding the collection of personal information by government institutions?

<p>Personal information must relate directly to an operating program or activity. (A)</p> Signup and view all the answers

According to Section 5 of the Privacy Act, how should government institutions collect personal information?

<p>From the individual to whom it relates, unless authorized otherwise. (D)</p> Signup and view all the answers

What is the primary focus of the OTIMROEPMQ Codes of Ethics related to patient information?

<p>Ensuring the confidentiality and integrity of patient information. (A)</p> Signup and view all the answers

What purpose does the Privacy Act serve in protecting individual privacy?

<p>It enhances the rights of individuals to access their own personal information held by government institutions. (A)</p> Signup and view all the answers

What should government institutions do regarding the retention of personal information after it is used, according to Section 6 of the Privacy Act?

<p>Retain it for a specified period post-usage. (A)</p> Signup and view all the answers

Flashcards

Definition (in Radiography)

The sharpness or clarity of detail in an image. It's a measure of how well an image reproduces fine structures and edges.

Objective Definition

The sharpness or clarity of an image based on objective measurements like unsharpness or resolution. It's independent of human perception.

Subjective Definition

Subjective definition refers to the perceived sharpness of an image based on a human observer's interpretation. It can be influenced by various factors, including contrast, noise, and viewing conditions.

Resolving Power

The ability of an imaging system to reproduce fine details and edges. This is a crucial aspect of image quality, as it determines how clearly small structures can be visualized.

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Unsharpness

The degree of blur or fuzziness in an image. It can be measured to quantify the sharpness of an image.

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Motion Unsharpness (Um)

The blur caused by the movement of the object being imaged. It's often the biggest contributor to overall image unsharpness.

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Intrinsic Unsharpness

The blur caused by the inherent limitations of the imaging system.

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Absorption Unsharpness (Ua)

The blur caused by the oval shape of some organs, like kidneys.

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Total Unsharpness (Ut)

The sum of all types of unsharpness in an image. It's the overall blur you see.

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Resolution Test Pattern (RTP)

A tool used to objectively measure the sharpness of an image, providing a numerical value.

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What is the relationship between the actual focal spot (AFS) and the effective focal spot (EFS)?

The actual focal spot (AFS) is the area on the anode where electrons strike and produce x-rays. The effective focal spot (EFS) is the projected size of the AFS onto the patient. The EFS is smaller than the AFS, and it is influenced by the angle of the anode.

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How does the angle of the anode affect the effective focal spot size?

The angle of the anode affects the size of the EFS. A smaller anode angle results in a smaller EFS. However, decreasing the anode angle also reduces the field of view. In general, x-ray tubes have anode angles between 13 and 15 degrees.

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Why is faster anode rotation beneficial for smaller focal spot sizes?

The anode rotates to dissipate heat generated by the electron bombardment. Faster rotation cools the anode more effectively, allowing for smaller focal spot sizes.

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Explain the line focus principle and its effect on the effective focal spot size.

The line focus principle describes how the effective focal spot size varies along the central ray. The effective focal spot size is larger on the cathode side because the electrons are spread out due to the steeper angle. On the anode side, the effective focal spot is smaller because the electrons are concentrated due to the shallower angle.

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How does the object-to-image distance (OID) affect the effective focal spot size?

The object-to-image distance (OID) is the distance between the object being imaged and the image receptor. Decreasing the OID reduces the magnification of the image and, consequently, the effective focal spot size. This means that minimizing OID can improve image sharpness. For example, when imaging the orbits, the PA projection has a smaller OID than the AP projection, resulting in less magnification and a smaller EFS.

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What is the basic function of a digital image receptor?

A digital image receptor converts x-ray photons into an electronic signal, which is then processed and displayed as an image.

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How do direct DR systems work?

Direct DR systems use a detector that directly converts x-ray photons into an electronic signal, typically using a-Se (amorphous selenium) material.

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How do indirect DR systems work?

Indirect DR systems use a scintillator to convert x-ray photons into light, which is then captured by a CCD or CMOS sensor to produce an electronic signal.

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What is wide dynamic range in digital radiography?

The ability of a digital imaging system to record a wide range of radiation exposures, producing detail in both light and dark areas of the image.

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What is a digital image histogram?

The digital image histogram is a graph that shows the distribution of pixel intensities in a digital image, representing the frequency of each pixel value.

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How does the pixel count per shade of gray affect image quality?

The # of pixels per shade of gray affects the overall quality of an image on a histogram. It dictates the 'smoothness' of the image and how fine details can be represented.

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How does collimation impact histogram analysis?

The collimated area determines the scope of information included in the image. It helps create more precise histograms and thus enhances image quality.

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What are image processing algorithms in radiology?

Algorithms are the set of instructions executed by a computer to achieve a specific task. In radiology, algorithms are used to process the image, enhancing sharpness and contrast while reducing post-processing. These algorithms are known as 'Look Up Tables' (LUT).

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What is the Exposure Index Value (EIV) and why is it important?

The Exposure Index Value (EIV) measures the overall amount of energy embedded in the image. It's an indicator of proper exposure, ensuring optimal image quality and patient dose.

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What are post-processing functions in radiography?

Post-processing functions involve various tasks applied to the image AFTER acquisition, aiming to optimize the image and make it suitable for interpretation and storage.

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What is a CCD?

A light-sensitive element that converts light signals into electrical signals (electrons).

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What is meant by a CCD's "Wide Dynamic Range"?

The amount of light a CCD can detect ranges from very dim to very bright.

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What is the "DEL" in a CCD?

The size of the individual sensing elements in a CCD, determining the level of detail captured in an image.

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What is Indirect Conversion in digital radiography?

This type of digital radiography uses a scintillator, such as CsI, to convert X-ray photons into light, and then a CCD to convert the light into an electrical signal.

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What is Direct Conversion in digital radiography?

This method directly converts X-ray photons into an electrical signal without the use of a scintillator.

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Study Notes

Radiographic Noise Definition & Types

  • Radiographic noise is an unwanted fluctuation in an image that obscures the visibility of structures.
  • Noise is a stochastic component in the image, primarily resulting from scatter.

Image Mottle

  • Image mottle is a type of image noise and is categorized into three types:
    • Quantum mottle (quantum noise): Variations in photon concentration within a small image area due to random X-ray photon distribution. It appears as a grainy texture.
    • Electronic mottle (electronic noise): Fluctuations in the electrical signal caused by electronic circuits in the image receptor. Generally less significant than quantum mottle. Digital radiography (DR) systems typically reduce or eliminate this noise by preprocessing.
    • Structured mottle: Non-uniformity in the image receptor material (like phosphor crystals), often due to non-uniform coating or physical imperfections. Corrected through re-calibration (flat-field calibration).

Quantum Mottle (Quantum Noise)

  • The amount of quantum mottle is inversely proportional to the square root of the number of X-ray photons per image area.
  • More photons = less fluctuation.
  • Lower photon number in an area = greater fluctuation.
  • Low exposures, low contrast, high sharpness, and low brightness increase visibility of quantum mottle.
  • QM is the greatest contributor to image mottle.
  • QM is higher with sensitive IR.
  • QM is a main limiting factor of image quality.

Electronic Mottle (Noise)

  • Fluctuations in the electrical signal from the image receptor’s electronic circuits.
  • Generally less noticeable than quantum mottle.
  • Digital radiography (DR) systems typically reduce or eliminate this noise by preprocessing.

Structured Noise

  • Non-uniformity in the image receptor material, particularly in computed radiography (CR).
  • Often caused by non-uniform phosphor crystal coating/physical imperfections.
  • Corrected through re-calibration (flat-field calibration).

Sources of Unsharpness and their Factors

  • Geometric unsharpness (Ug): Due to the geometry of shadow formation.
    • Focal spot size (actual and effective), source-to-image distance (SID), object-to-image distance (OID), angle of the anode.
  • Motion unsharpness (Um): Movement of the patient or equipment during exposure.
    • Voluntary or involuntary patient movement, equipment vibration, and rate of movement.
  • Photographic unsharpness (Up): Factors within the imaging system itself. This is further discussed in CR/DR topics. Up is also related to the inherent response and properties of imaging receptors (e.g., PSPs, CCDs, a-Se).
  • Absorption unsharpness (Ua): Shape and composition of certain structures like the kidneys, or other tissues with varying radiographic densities, contributing to variations in image blurring. This unsharpness is noticeable with some diseases like arthritis.

Objective Measurement of Image Definition/Sharpness/Detail

  • Methods to objectively measure image sharpness:
    • Resolution test pattern (RTP).
    • Line spread function (LSF).
    • Modulation transfer function (MTF).

Resolution Test Pattern (RTP)

  • A quality control tool for measuring spatial resolution.
  • Consists of pairs of radiopaque and radiotransparent lines.
  • Used to measure spatial resolution as Line Pairs per millimeter (lp/mm).

Line Spread Function (LSF)

  • Method to measure spatial resolution.
  • Measures the blurring (unsharpness) related to the image's edges, primarily from edge response function (ERF). LSF analysis quantifies the blur along the edges of objects.

Modulation Transfer Function (MTF)

  • Measures the ability of the imaging system to preserve contrast/image details as spatial frequencies increase.
  • Fourier analysis is used to determine MTF. Limiting spatial frequency is determined at the 10% MTF point.

Other Key Terms/Factors

  • Effective Focal Spot (EFS): The focal spot as viewed from the central ray.
  • Actual Focal Spot (AFS): The actual physical size of the focal spot on the target.
  • Focal Spot Size (FS): Both the actual and effective focal spots.
  • SID: Source-to-image distance.
  • OID: Object-to-image distance.
  • mA (milliamperes): X-ray tube current.
  • kVp (kilovolts peak): X-ray tube potential.
  • Field of view (FOV): The area of the body part that is imaged.
  • Quantum Noise (QM): Noise that results from the random distribution of X-rays.
  • Electronic Noise: Noise originating from the components within the image receiver unit.
  • Structured Noise: Noise unique to the image receptor's physical structure.
  • OID: Object-to-Image receptor distance
  • SOD: Source to Image receptor distance
  • Line Pair per millimeter (Lp/mm): A measure of image resolution.

Total Unsharpness (Ut)

  • The combined effect of all unsharpness factors (geometric, motion, photographic, and absorption).

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