CT Imaging and Photon Counting Detectors

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Questions and Answers

What is the primary limitation of the absorption efficiency of a detector using an antiscatter grid?

  • The area fill fraction of the septa (correct)
  • The thickness of the scintillator
  • The response time of the scintillator
  • The quantum noise at low signal levels

What is the primary source of noise in scintillator/photodiode detectors at low signal levels?

  • Quantum noise
  • Detector dead time
  • Electronic noise (correct)
  • Scatter radiation

What is the advantage of using direct conversion materials like CdTe or CZT in photon counting detectors?

  • They have a higher absorption efficiency for X-rays.
  • They are less susceptible to electronic noise.
  • They have a faster response time than scintillator/photodiode combinations.
  • They produce a larger charge signal for each X-ray photon. (correct)

What is the CT number for air?

<p>-1000 HU (D)</p>
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Why does bone not have a unique CT number?

<p>Both A and B (D)</p>
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How do photon counting detectors achieve improved contrast-to-noise ratio (CNR)?

<p>By counting the number of X-ray photons instead of integrating their energy. (D)</p>
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What is the purpose of a window/level operation in CT imaging?

<p>To adjust the contrast and brightness of the image. (A)</p>
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What is the primary reason for considering photon counting detectors in CT?

<p>They allow for the measurement of X-ray photon energy. (D)</p>
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How do photon counting detectors mitigate the impact of electronic noise?

<p>By defining a detection threshold to exclude low-energy signals. (B)</p>
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What is the purpose of the scintillator material in a CT detector?

<p>To convert X-rays into visible light. (D)</p>
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How does the ability to measure X-ray photon energy contribute to improved CNR in photon counting detectors?

<p>It allows for the weighting of low-energy photons to enhance contrast. (A)</p>
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What is the difference between a helical and a multi-slice CT scanner?

<p>A helical CT scanner takes a series of images in a spiral pattern, while a multi-slice CT scanner takes multiple images simultaneously. (C)</p>
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What is the CT number defined as?

<p>The linear attenuation coefficient divided by the density of water. (C)</p>
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What is the typical sample rate for the data acquisition system (DAS) in a scintillator/photodiode detector?

<p>A few kilohertz (A)</p>
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Which of the following materials is NOT commonly used as a scintillator crystal in CT detectors?

<p>SiO2 (C)</p>
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Which of the following is NOT a benefit of using a multi-slice CT scanner compared to a single-slice scanner?

<p>Reduced radiation dose to the patient. (A)</p>
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What is the primary source of noise in CT images?

<p>Quantum noise (C)</p>
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What is the main factor determining the beam width in CT images at locations close to the focal spot?

<p>Focal spot size (B)</p>
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Which of these factors does NOT directly influence the spatial resolution of a CT image?

<p>Helical pitch (D)</p>
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How does the size of the focal spot affect the spatial resolution of a CT image?

<p>Smaller focal spots lead to higher spatial resolution (D)</p>
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What is the relationship between the voxel size and the spatial resolution of a CT image?

<p>Voxel size can be larger than the spatial resolution if computational efficiency is prioritized (C)</p>
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What is 'azimuthal blur' in CT imaging, and how does it affect image quality?

<p>Blurring caused by the continuous rotation of the tube-detector system, increasing with distance from the center of rotation (B)</p>
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What is the purpose of the reconstruction kernel in CT imaging?

<p>To enhance high frequencies for sharper images or suppress high frequencies for noise reduction (D)</p>
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Which of these factors does NOT contribute to the quantum noise in CT images?

<p>The size of the detector channels (C)</p>
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What causes streak artifacts during the acquisition of measurements?

<p>A short movement of an object (C)</p>
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What primarily results in a blurred representation of moving parts in helical CT?

<p>Gradual movement, such as cardiac motion (A)</p>
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What is a characteristic of stairstep artifacts in helical CT?

<p>They are caused by large helical pitch or small reconstruction intervals. (D)</p>
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What is meant by the term 'windmill artifact' in CT imaging?

<p>A z-aliasing artifact occurring primarily in helical cone-beam CT. (D)</p>
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Which of the following best describes blooming artifacts?

<p>Occurs primarily due to beam hardening and limited spatial resolution. (A)</p>
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Under what condition are artifacts likely to occur due to poor calibration in a CT system?

<p>When the detector efficiency changes between calibration and measurement. (D)</p>
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What may cause metal artifacts in imaging?

<p>The presence of metal implants and beam hardening. (B)</p>
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What effect does a large helical pitch have on imaging?

<p>It can result in stairstep artifacts during reconstruction. (D)</p>
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What effect does increasing the mA s have on the SNR in imaging?

<p>It increases SNR and increases patient dose. (A)</p>
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Which factor primarily determines the contrast between an object and its background?

<p>Attenuation properties. (B)</p>
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What phenomenon occurs when the number of detector samples taken is insufficient?

<p>Aliasing. (A)</p>
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How does beam hardening affect the X-ray beam as it passes through tissue?

<p>It results in the preferential absorption of low-energy photons. (B)</p>
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What percentage of the detected radiation typically results from scatter?

<p>Up to 30%. (B)</p>
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What effect do scattered photons have on the measured intensity profile?

<p>They yield streak artifacts. (D)</p>
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What is the significance of the nonlinear partial volume effect in imaging?

<p>It averages intensity across the beam width. (D)</p>
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What is a primary reason CT scans are better at detecting low-contrast details than radiography?

<p>CT scans create projection images of thin body slices. (D)</p>
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What is the purpose of the collimator in computed tomography?

<p>To focus the X-ray beam into a thin slice (A)</p>
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What is the principle behind image formation in computed tomography?

<p>The X-ray beam is attenuated differently by different tissues (A)</p>
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What is the difference between parallel-beam geometry and fan-beam geometry in CT?

<p>Parallel-beam geometry uses a narrower X-ray beam than fan-beam geometry. (C)</p>
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Which of the following statements about the history of computed tomography is correct?

<p>Linear tomography was developed before the invention of computed tomography. (A)</p>
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What is the main difference between computed tomography and conventional radiography?

<p>CT produces three-dimensional images, while conventional radiography produces two-dimensional images. (C)</p>
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How does axial transverse tomography differ from linear tomography?

<p>Axial transverse tomography rotates the patient and the film, while linear tomography moves the patient and the film in opposite directions. (D)</p>
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Why is computed tomography sometimes referred to as CAT?

<p>Because it uses a computer to generate the images. (D)</p>
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Which of the following examples demonstrates how CT scans improve patient care?

<p>CT scans can be used to diagnose a wider range of medical conditions than conventional X-rays. (B), CT scans provide more detailed information about bone fractures than conventional X-rays. (C)</p>
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What does the term 'tomography' originate from?

<p>Greek words for 'slice' and 'to write' (D)</p>
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In computed tomography, what is the process of acquiring X-ray attenuation measurements at various angles called?

<p>Scanning (C)</p>
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Which of the following is NOT a type of geometry used for X-ray beams in computed tomography?

<p>Conical-beam geometry (A)</p>
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What is the primary reason why CT scans are often better at detecting low-contrast details compared to radiography?

<p>CT scans provide detailed cross-sectional images, enhancing the visibility of small differences in tissue density. (C)</p>
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What is the significance of the term 'CAT' in relation to CT?

<p>It stands for 'Computed Axial Tomography' and highlights the use of axial imaging in the technique. (D)</p>
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Which of the following is an example of how CT scans have improved patient care?

<p>All of the above. (D)</p>
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What is a primary characteristic of the simple backprojection reconstruction method?

<p>It produces blurred images of sharp features. (D)</p>
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What advantage does the convolution method of filtered backprojection offer during image reconstruction?

<p>It can construct images while data are being collected. (A)</p>
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Which of the following is NOT a type of reconstruction algorithm mentioned?

<p>Radial projection (B)</p>
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What is the primary function of a deblurring function in the filtered backprojection method?

<p>To remove frequency components causing blurring. (D)</p>
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In the series expansion reconstruction technique, how is the data from different angular orientations utilized?

<p>Differences in measurements are integrated into the appropriate elements. (B)</p>
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Which method is most commonly used for image reconstruction in CT today?

<p>Filtered backprojection (C)</p>
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What type of integral equation does the filtered backprojection method employ?

<p>One-dimensional integral equation (B)</p>
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Which of the following terms is associated with variations of the series expansion method?

<p>Algebraic reconstruction technique (C)</p>
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What primary advantage do photon counting detectors have over scintillator/photodiode detectors?

<p>They use direct conversion materials for higher charge production. (A)</p>
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How does photon counting improve the contrast-to-noise ratio (CNR) in imaging?

<p>By precisely counting individual photons instead of averaging. (A)</p>
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What is a significant drawback of using a transimpedance amplifier in the data acquisition system?

<p>It is susceptible to introducing electronic noise. (D)</p>
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What is the typical absorption efficiency of a scintillator in the context provided?

<p>96% (A)</p>
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Why does electronic noise dominate over quantum noise in scintillator/photodiode detectors at low signal levels?

<p>The electronic noise generated is inherently higher. (C)</p>
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What primarily determines the spatial resolution in a CT image?

<p>The size of the focal spot (D)</p>
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What is the role of direct conversion materials like CdTe or CZT in photon counting detectors?

<p>They enhance the count and energy measurement of X-ray photons. (C)</p>
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Which type of noise in CT imaging is primarily due to the statistical nature of X-rays?

<p>Quantum noise (A)</p>
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What is the impact of defining a detection threshold in photon counting detectors?

<p>It reduces the influence of electronic noise on the detected signals. (A)</p>
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How does the size of the detector channels influence CT image quality?

<p>Detector channel size affects channel-to-channel crosstalk (C)</p>
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What factor primarily limits the absorption efficiency in detectors using an antiscatter grid?

<p>The area fill fraction of the septa. (A)</p>
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What is the effect of azimuthal blur in CT imaging?

<p>It increases linearly with distance from the center of rotation (A)</p>
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What happens if the voxel size chosen in CT imaging is larger than the spatial resolution of the system?

<p>It may determine the spatial resolution instead (C)</p>
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What type of noise is typically considered the main contributor in CT imaging?

<p>Statistical noise (D)</p>
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Which factor primarily impacts the beam width in CT imaging?

<p>The focal spot size and detector cell size (D)</p>
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What is the role of the reconstruction kernel or convolution filter in CT imaging?

<p>To enhance or suppress image frequencies (D)</p>
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What technology was the first CT scanner based on?

<p>EMI scanner technology (C)</p>
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What does the CT number for soft tissue typically represent?

<p>A range depending on tissue composition (D)</p>
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What is the primary function of the scintillator material in modern CT detectors?

<p>To convert X-rays into visible light (C)</p>
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Which of these factors influences the mass attenuation coefficient for bone?

<p>The energy of the absorbed X-rays (B)</p>
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In CT imaging, what is the purpose of the window and level settings?

<p>To define the displayed gray level interval (B)</p>
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What is a key characteristic of bone in terms of CT imaging?

<p>Bone's CT number varies due to its composition (D)</p>
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How many pixels typically make up the images in modern CT scanners?

<p>512 × 512 (D)</p>
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Which component is essential in the construction of a scintillator detector matrix?

<p>Photodiode (D)</p>
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What effect does increasing the mA s have on signal-to-noise ratio (SNR) in imaging?

<p>Increases SNR, reducing relative quantum noise (A)</p>
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Which of the following factors primarily affects the contrast between an object and its background?

<p>The various physical factors such as beam hardening and scatter (A)</p>
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What is a consequence of undersampling in image acquisition?

<p>Sharp edges in projections being poorly approximated (C)</p>
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How does beam hardening impact the characteristics of the X-ray beam?

<p>It causes a beam to become less attenuated as it interacts with tissues (A)</p>
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What percentage of the detected radiation in a CT scan is typically attributed to scatter?

<p>About 30% (B)</p>
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What does the nonlinear partial volume effect result from in imaging?

<p>The averaging of intensity over finite beam width (B)</p>
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What artifact may occur due to scatter during imaging?

<p>Streak artifact (C)</p>
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Which of the following best describes the impact of digital gray level transformation (window/level) on contrast?

<p>It reduces the perceptibility of low-contrast details (C)</p>
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What is the main difference between conventional radiography (x-ray) and computed tomography (CT)?

<p>Conventional radiography produces a 2D image, while CT produces a series of cross-sectional images that can be reconstructed into a 3D image. (D)</p>
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What is the term 'tomography' derived from?

<p>Greek words for 'slice' and 'writing' (B)</p>
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Which of the following procedures is NOT used in computed tomography?

<p>A single X-ray beam is used to create a 2D image. (A)</p>
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What is the primary reason CT scans are superior to conventional radiography in detecting low-contrast details?

<p>CT scans use specialized algorithms to reconstruct cross-sectional images, enhancing the visualization of subtle differences in tissue density. (D)</p>
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What is the main difference between axial transverse tomography and linear tomography?

<p>Axial transverse tomography produces a series of cross-sectional images, while linear tomography produces a single image of a specific plane. (A)</p>
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Which of the following is a key advantage of using a fan-beam geometry in CT compared to a parallel-beam geometry?

<p>Fan-beam geometry allows for faster data acquisition. (A)</p>
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Which of the following statements BEST describes the process of reconstructing a function from its projections in CT?

<p>A mathematical algorithm is used to process the line attenuation measurements taken at various angles, reconstructing the 3D image. (A)</p>
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Which of the following is a major limitation of detectors using scintillator/photodiode combinations at low signal levels?

<p>Susceptibility to electronic noise from the transimpedance amplifier (A)</p>
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What is the primary advantage of using direct conversion materials like CdTe or CZT in photon counting detectors over scintillator/photodiode combinations?

<p>Significantly higher charge production per X-ray photon (A)</p>
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How do photon counting detectors achieve improved contrast-to-noise ratio (CNR) compared to conventional detectors?

<p>By eliminating electronic noise through careful thresholding and counting individual photons (D)</p>
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What is a significant advantage of photon counting detectors in CT, beyond their improved contrast-to-noise ratio?

<p>They can measure the energy of individual X-ray photons (B)</p>
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Which of these statements is TRUE about how photon counting detectors impact contrast-to-noise ratio (CNR)?

<p>They improve CNR by reducing the influence of electronic noise, resulting in cleaner images (C)</p>
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How does the finite thickness of the septa in an antiscatter grid limit the absorption efficiency of a detector?

<p>By limiting the area fill fraction, decreasing the overall collection efficiency (D)</p>
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What is the key principle behind the ability of photon counting detectors to count individual photons?

<p>They detect the charge produced by each photon, allowing for discrimination based on energy (D)</p>
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What type of transformation is used to convert a function f(x, y) into its sinogram p(r, θ)?

<p>Radon Transform (C)</p>
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What is the significance of the sinogram in computed tomography?

<p>It is a 2D dataset created by stacking projections of the object at different angles. (A)</p>
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Why is it sufficient to measure projection profiles p θ (r) for θ ranging from 0 to π in parallel-beam geometry?

<p>Because the projection profiles measured at opposite sides are redundant. (C)</p>
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What is the relationship between the measured intensity profile and the attenuation profile in CT?

<p>The attenuation profile is the logarithm of the measured intensity profile. (C)</p>
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Why does the projection function p(r, θ) for a single dot have a sinusoidal shape?

<p>Because the projection process involves line integrals along different angles. (C)</p>
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What does the coordinate system (r, θ) represent in the context of the Radon transform?

<p>The angle of the X-ray beam and the distance from the origin. (C)</p>
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How does the Fourier transform contribute to CT image reconstruction?

<p>It is used to separate the frequency components of the attenuation pattern. (D)</p>
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What is the purpose of the Radon transform in CT?

<p>To convert the measured projection data into a sinogram. (B)</p>
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Which reconstruction method is considered the most popular and commonly used in CT today?

<p>Filtered backprojection (C)</p>
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What is the primary limitation of the simple backprojection method for image reconstruction?

<p>It produces blurred images of sharp features in the object. (B)</p>
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In the filtered backprojection method, what is the purpose of the deblurring function?

<p>To remove or reduce the blurring inherent in the backprojection process. (D)</p>
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What is the main difference between 'simple backprojection' and 'filtered backprojection' reconstruction methods?

<p>Simple backprojection reconstructs the image directly from the raw data, while filtered backprojection uses a deblurring function to reduce blurring before backprojection. (B)</p>
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Which of these is NOT a variation of the series expansion technique for image reconstruction?

<p>FFT (fast Fourier transform) (A)</p>
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In the series expansion technique, how is the reconstructed image obtained?

<p>By iteratively comparing attenuation data at different angles and adjusting corresponding elements in the image. (B)</p>
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Which of the following statements BEST describes the relationship between x-ray attenuation data and the reconstructed image in CT?

<p>The x-ray attenuation data is used to calculate the CT numbers, which are then assigned to corresponding pixels to form the reconstructed image. (A)</p>
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What is the primary advantage of using an iterative reconstruction method in CT?

<p>Ability to reconstruct images from incomplete data sets or with lower radiation doses. (A)</p>
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Which factor primarily determines the beam width in CT images at locations close to the focal spot?

<p>Focal spot size (B)</p>
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Which of the following is NOT a common type of scintillator crystal used in CT detectors?

<p>NaCl (D)</p>
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What does the 'window' in window/level operation in CT imaging refer to?

<p>The width of the displayed gray level interval (D)</p>
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What is the primary function of the photodiode in a CT detector?

<p>Convert visible light into an electrical signal (D)</p>
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What is the reason for bone not having a unique CT number?

<p>The composition and structure of bone vary, affecting its attenuation. (B)</p>
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Why is the introduction of helical and multi-slice CT significant?

<p>They allowed for faster scanning and higher spatial resolution. (C)</p>
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Which of the following best describes the relationship between CT number and linear attenuation coefficient?

<p>The CT number is directly proportional to the linear attenuation coefficient. (C)</p>
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Flashcards

X-ray Attenuation

The reduction of X-ray intensity as it passes through materials, crucial for CT imaging.

Spatial Resolution

The ability to distinguish small details in an image; affected by focal spot size and detector channel size.

Focal Spot

The area on the anode where electrons hit, originating the X-rays; impacts image quality.

Azimuthal Blur

Blurring that increases with distance from the center of rotation during continuous rotation of the tube-detector.

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Reconstruction Kernel

A filter in image reconstruction that sharpens high frequencies or reduces noise in CT images.

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Voxel Size

The 3D equivalent of a pixel, chosen smaller than system resolution for accurate imaging.

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Quantum Noise

Statistical noise in CT primarily from the nature of X-ray photons, represented by a Poisson distribution.

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Types of Noise

Includes quantum noise, electronic noise, and round-off noise that affect image quality in CT.

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Computed Tomography (CT)

An imaging modality producing cross-sectional images based on X-ray attenuation.

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Tomography

Derived from Greek meaning 'to write slices', it refers to imaging techniques that produce slice images of objects.

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X-ray Tube

Device that produces X-rays, essential for CT imaging.

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Attenuation

Reduction of the intensity of X-rays as they pass through the body, critical in CT image formation.

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Detector

Measures the X-ray intensity after it has been attenuated by the patient.

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Fan-beam Geometry

A scanning technique in CT where X-rays spread in a fan-like shape across the patient's body.

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Linear Tomography

A type of tomography where the X-ray source and film move at constant speed in opposite directions.

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Axial Transverse Tomography

A CT technique where the film is positioned horizontally and both patient and film rotate around a vertical axis.

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Focal Plane

The plane in focus during CT rotation, while others are averaged out.

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EMI Scanner

The first CT scanner, developed by Godfrey Hounsfield in 1972.

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Hounsfield Units (HU)

CT numbers reflecting tissue density, used for imaging analysis.

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Linear Attenuation Coefficient

A measure related to the absorption of X-rays by different tissues.

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Window/Level Operation

A technique to optimize the gray level display in CT imaging.

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Scintillator Crystal

Material converting X-rays into visible light in CT detectors.

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Energy Integrating Detectors

CT detectors that generate electric current from scintillations.

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Multi-Slice CT

CT technology introduced in 1998, enabling multiple slices at once.

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Signal-to-Noise Ratio (SNR)

Ratio that compares the level of a desired signal to the level of background noise.

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Image Contrast

The difference in shading between an object and its background, influenced by attenuation.

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Window/Level Transformation

Technique to enhance displayed image contrast in digital images.

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Undersampling

Taking insufficient detector samples leading to artifacts like aliasing.

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Beam Hardening

Phenomenon where low-energy photons are absorbed more, causing the beam to harden.

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Scatter

Photons deviating from their original path, causing inaccuracies in intensity measurements.

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Nonlinear Partial Volume Effect

Effect caused by finite beam width leading to averaged intensity measurements.

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E-Motion Artifacts

Inconsistent measurements caused by small movements of an object during acquisition.

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Streak Artifacts

Visible lines resulting from object movement during imaging, causing distortion.

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Cardiac Motion Effects

Blurred representation of moving parts from gradual movements like the heart.

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F-Stairstep Artifact

Artifacts in helical CT due to large helical pitch or small reconstruction intervals.

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G-Windmill Artifact

Z-aliasing artifact with a pattern like spokes due to cone-beam CT interpolation.

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Calibration Issues

Artifacts caused by poor calibration or detector failure during imaging.

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Metal Artifacts

Artifacts from beams hardening and scattering caused by metal implants.

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Blooming Artifact

Overestimation of calcified plaque size caused by beam hardening and resolution limits.

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Scintillators

Materials that produce light when absorbing radiation, enabling detection.

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Absorption Efficiency

The percentage of radiation absorbed by a detector material, indicating its effectiveness.

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Photodiode

A semiconductor device that converts light into an electrical current.

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Data Acquisition System (DAS)

A system that collects and processes data from detectors to produce readable signals.

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Transimpedance Amplifier

An electronic device that converts current from a photodiode to voltage.

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Electronic Noise

Unwanted signals that interfere with the detection and processing of useful signals.

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Photon Counting Detectors

Devices that count individual photons and detect their energy, improving CNR.

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Charge Measurement in Detectors

The ability of a detector to determine the charge related to each photon impact, improving accuracy.

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Mass Attenuation Coefficient

A measure of how much a material can attenuate X-rays, varies with tissue type.

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CT Number

A value representing tissue density in Hounsfield Units (HU), affects image quality.

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Window/Level Setting

A technique to optimize image contrast by adjusting the range of displayed gray levels.

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3D Imaging

Technique that allows visualization of structures in three dimensions using CT data.

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Dynamic (4D) Studies

Advanced imaging that includes time as a factor, showing motion within a scan.

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X-ray Computed Tomography

An imaging modality producing cross-sectional images using X-ray attenuation.

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Tomography Origin

The term tomography derives from Greek words meaning 'to write slices'.

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Detector Array

An array of detectors that measure X-ray intensity after attenuation by the patient.

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Reconstruction Process

The method of reconstructing the actual attenuation at each point from measurements taken at various angles.

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History of CT

Computed tomography originated in the late 20th century, building on earlier imaging technologies.

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Image Reconstruction

The process of creating a spatially correct image from x-ray data using techniques like backprojection.

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Simple Backprojection

A method where x-ray paths are divided into elements, summing their contributions to create an image, but often blurs sharp features.

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Filtered Backprojection

An advanced technique that uses a filter to remove blurring from x-ray data before reconstructing the image.

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Convolution Method

In image reconstruction, it’s where a deblurring function is combined with x-ray data to improve image clarity.

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Series Expansion

A reconstruction method where x-ray data from different angles are compared and combined to refine image quality.

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Algebraic Reconstruction Technique (ART)

A variation of series expansion that refines images using data from multiple angles to enhance details.

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Iterative Least-Squares Technique (ILST)

A series expansion method that minimizes the error between the estimated image and actual data.

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Simultaneous Iterative Reconstruction Technique (SIRT)

A series expansion technique that refines image reconstruction by simultaneously processing data from multiple angles.

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Total Exposure

The amount of radiation received by the patient during imaging; affects noise and SNR.

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Attenuation Properties

Characteristics that determine how much radiation an object can absorb or scatter.

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Gray Level Transformation

A process that adjusts pixel brightness in digital images to enhance contrast.

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Aliasing

A phenomenon caused by undersampling, resulting in distorted or misrepresented images.

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X-ray Beam Width

The width of the X-ray beam influenced by focal spot and detector size.

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Detector Channel Size

The dimensions of the individual channels in a CT detector, affecting resolution.

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Spatial Resolution Factors

Elements influencing clarity in CT images, including focal spot size and voxel size.

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Interpolation Process

The method used in backprojection that relies on sample density for image reconstruction.

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Focal Spot Size Dominance

At close range to the focal spot, its size greatly impacts beam width.

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Channel-to-Channel Crosstalk

Interference between detector channels that affects image quality.

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Types of Noise in CT

Including quantum noise, electronic noise, and round-off noise affecting image quality.

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Poisson Distribution in Quantum Noise

Describes the statistical nature of quantum noise measured in CT imaging.

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Scintillator Efficiency

A measure of how well scintillators convert radiation into detectable light.

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Photon Counting

A method in detectors that counts individual photons rather than integrating their energy.

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Direct Conversion Materials

Materials like CdTe and CZT that directly convert X-rays to electronic charges.

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Charge to Energy Relation

The principle that relates the amount of charge produced to the energy of the incoming X-ray.

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CNR Improvement

The enhancement of contrast-to-noise ratio achieved by photon counting detectors.

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Detection Threshold

A predefined limit that improves signal detection by eliminating electronic noise effects.

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Electronic Noise in Detectors

Unwanted signals that interfere with capturing actual photon signals in detectors.

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Mediating Low-Energy X-rays

Assigning greater importance to lower-energy X-ray detection to boost contrast.

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CT Number (CTN)

Value representing tissue density in imaging; varies with composition and structure.

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Scintillator Properties

Scintillators have high optical quality for efficient light transfer and high absorption efficiency.

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Charge Measurement Importance

Detectors quantify the charge per X-ray, enhancing energy detection accuracy.

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Absorption Efficiency in Scintillators

A measure of how effectively scintillators absorb radiation, typically around 96%.

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Image Quality

The overall clarity and detail in CT images, influenced by several factors.

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Voxel Size Effects

Voxel size impacts spatial resolution; smaller sizes provide finer detail.

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Reconstruction Data Convergence

Process where data from different angles combine for accurate image creation.

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Noise Contribution in CT

Sources of noise like quantum and electronic noise that degrade image quality.

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Azimuthal Blur Reduction

Blurring caused by rotational motion, particularly at image edges, affecting quality.

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Backprojection Variants

Different methods of reconstructing images, including simple and filtered types for better results.

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CT Image Formation

CT images are produced by X-ray attenuation measured at various angles.

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Direct Conversion Detectors

Detectors that directly convert X-rays into electronic signals for CT imaging.

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Radon Transform

A mathematical transformation that converts a function into its sinogram in CT imaging.

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Sinogram

A 2D dataset that results from stacking projections of a function obtained at different angles.

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Projection Function pθ(r)

Represents the intensity profile of X-ray beams for a specific angle in CT.

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Angle θ in CT

The angle at which X-ray beams are measured relative to the patient.

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Count Rate Limits

The maximum rate that a detector can accurately count incoming X-ray photons.

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Intensity Profile I(r)

The measurement of X-ray intensity received at different positions (r) during imaging.

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Fourier Transform in CT

A method to separate X-ray attenuation patterns into frequency components for analysis.

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Reconstruction Algorithm

Mathematical methods for creating images from X-ray data in CT.

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Related Documents

ch6(1).pdf

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