CT Physics And Instrumentation Quiz Questions And Answers

A pixel is a term used to describe a picture element. It refers to the smallest unit of a digital image or display that can be individually manipulated. Each pixel represents a specific color or shade, and when combined with other pixels, it forms the complete image. Therefore, the correct answer is "a picture element."

Pixels representing tissues with average attenuation coefficients greater than that of water have positive values. This is because attenuation coefficients represent the ability of a material to absorb or scatter radiation, and tissues with higher attenuation coefficients than water absorb more radiation. Therefore, the pixel values representing these tissues will be positive, indicating the presence of higher attenuation.

Interpolation is the correct answer because it is the mathematical technique used to estimate an unknown value based on known values on either side of it. It involves constructing a function that fits the known data points and then using that function to find the value of the unknown point. This technique is commonly used in various fields such as mathematics, statistics, and computer science to fill in missing data or to make predictions based on existing data.

Thermionic emission is the process by which electrons are produced at the cathode of a CT x-ray tube. This process involves heating the cathode, causing the release of electrons due to the increased thermal energy. These emitted electrons then travel towards the anode, where they interact with the target material and produce x-rays. Rectification refers to the conversion of alternating current to direct current, anode heel effect is the uneven distribution of x-rays due to the angle of the anode, and isotropic emission is not a recognized term in relation to x-ray production.

The High Frequency generator is usually located inside the gantry of a modern CT scanner. This placement allows for efficient and direct power supply to the X-ray tube, which is also located in the gantry. By having the generator inside the gantry, it reduces the need for long cables and minimizes energy loss, resulting in more accurate and reliable imaging. Additionally, having the generator within close proximity to the X-ray tube allows for better control and synchronization of the scanning process.

The given options represent different matrix sizes that can be used with a modern CT Scanner. A higher matrix size indicates a higher resolution, allowing for more detailed images. The size 80x80 is significantly smaller compared to the other options, suggesting that it would not be a typical matrix used with a modern CT Scanner.

The device constructed to house the x-ray tube and data acquisition system for a CT scanner is called a gantry. The gantry is a large, circular structure that rotates around the patient during a CT scan. It houses the x-ray tube, detectors, and other components necessary for capturing the images. The gantry plays a crucial role in positioning and moving the x-ray tube and detectors to acquire the necessary data for creating detailed cross-sectional images.

CTDI stands for Computed Tomography Dose Index, which is a measurement used to describe the radiation dose received by the patient during a CT scan. It is an important parameter in assessing the safety and potential risks associated with CT imaging. By measuring the radiation dose, healthcare professionals can ensure that the benefits of the CT scan outweigh the potential harm caused by radiation exposure. Therefore, the correct answer is "the radiation dose to the PT during the CT scan."

Filtered back projection is the most commonly used reconstruction method in modern CT scanners. It involves passing the raw projection data through a filter to enhance the image quality and then back projecting it to reconstruct the image. This method is preferred because it is fast, efficient, and provides good image quality. Back projection, iterative methods, and Fourier transform are also used in CT reconstruction, but they are not as commonly used as filtered back projection.

Spatial resolution, contrast resolution, and noise are all components of CT image quality that can be controlled by the technician. Spatial resolution refers to the ability of the CT scanner to distinguish between small objects or structures in the image. Contrast resolution refers to the ability of the scanner to differentiate between tissues with similar densities. Noise refers to the random variations in pixel values that can reduce image quality. Technicians can adjust the scanning parameters to optimize these components and improve the overall image quality.

Silver halide is not commonly used as a CT scintillation detector because it has a low light output and poor energy resolution compared to other materials. Ceramic rare earth, bismuth germanate, and cadmium tungstate are commonly used as CT scintillation detectors due to their high light output and good energy resolution, making them more suitable for detecting and measuring radiation in CT scans.

Ring artifacts on a CT image are associated with the rotate-rotate tube detector relationship. In this relationship, both the X-ray tube and the detector rotate simultaneously around the patient, capturing data from different angles. Ring artifacts occur when there are inconsistencies or errors in the data acquisition process, resulting in variations in the intensity values along the reconstructed image. These variations appear as rings or circular patterns on the CT image.

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In 1917, the Austrian mathematician Radon proved that it was possible to reconstruct a three-dimensional object from the infinite set of all projections. This means that by using a collection of two-dimensional images or projections of an object taken from different angles, it is possible to mathematically reconstruct the original three-dimensional object. This breakthrough in mathematics and imaging has had significant applications in fields such as medical imaging, computer vision, and industrial inspection.

The correct answer is 350-600 HU. This range is the average window width for an abdomen. HU stands for Hounsfield units, which is a measurement used in CT scans to determine the density of tissues. This range is commonly used to visualize the abdominal organs and structures, as it allows for differentiation between different types of tissues and helps in detecting abnormalities or pathologies in the abdomen.

The primary interaction between x-ray photons and tissue during a CT examination is the Compton effect. This occurs when an incoming x-ray photon interacts with an outer-shell electron in the tissue, causing the photon to scatter and lose some of its energy. This scattering effect is what allows CT scanners to create detailed images of the internal structures of the body. The other options mentioned, such as the Bremsstrahlung effect, characteristic effect, and coherent scatter, are also interactions between x-ray photons and tissue, but they are not the primary interaction in CT examinations.

A 512x512 image consists of 262,144 pixels. This is because to calculate the total number of pixels in an image, we multiply the number of pixels in the width (512) by the number of pixels in the height (512), resulting in 262,144 pixels in total.

A straight line appearing vertically on the scanogram of a fourth generation CT scanner is most likely caused by a detector malfunction. This means that there is an issue with the detector that is responsible for capturing the x-ray signals. This malfunction can result in a straight line artifact appearing on the scanogram. It is important to address this issue as it can affect the accuracy and quality of the CT scan images.

Low spatial frequencies represent areas of the CT image that contain minimal changes in tissue density. This is because low spatial frequencies correspond to large-scale structures and smooth variations in density. In contrast, high spatial frequencies represent areas with rapid changes in density, while positive and negative CT numbers indicate the relative density of tissues compared to water. Therefore, the correct answer is low spatial frequencies.

Good PT-Tech communication is the best method to reduce respiratory motion of the CT image. This is because when the patient and the technician have clear and effective communication, the patient can be instructed on how to control their breathing during the scan. By coordinating breath-holds or shallow breathing, respiratory motion can be minimized, resulting in clearer and more accurate CT images. This method is non-invasive and does not require any additional equipment or medications.

The DFOV (Display Field of View) is used to determine the size of the displayed image on a monitor. In this case, the image has a matrix size of 320x320 pixels and each pixel has a dimension of .75 x .75 mm. To calculate the DFOV, we multiply the matrix size by the pixel dimension. Therefore, the DFOV would be 320 x .75 mm = 240 mm. Since 1 cm is equal to 10 mm, the DFOV would be 24 cm.

In CT imaging, Hounsfield Units (HU) measure radiodensity. Positive HU values indicate denser materials. Fat has negative HU values, while blood typically ranges from +30 to +70 HU. Tumors can vary, but often have higher HU values compared to blood. A HU of +1.9 is too low for fat or water, making tumor the most likely material in this context. Tumors can have a broad range of HU values, and +1.9, though on the lower end, suggests a tumor.

4th generation CT scanners use a rotate-stationary tube-detector configuration. In this configuration, the X-ray tube rotates around the patient while the detector remains stationary. This allows for faster scanning times and improved image quality compared to earlier generations. The rotate-stationary configuration also reduces the risk of motion artifacts and provides more accurate and detailed images.

CT (Computed Tomography) produces diagnostic images with improved low contrast resolution when compared with conventional X-ray. Low contrast resolution refers to the ability to distinguish between structures that have similar densities or shades of gray. CT scans use a combination of X-rays and advanced computer processing to create detailed cross-sectional images of the body. This allows for better visualization and differentiation of subtle differences in tissue density, which is especially important for detecting small abnormalities or lesions that may not be easily seen on a conventional X-ray.

The Hounsfield value of a pixel is directly related to the attenuation coefficient of the material through which the X-ray beam passes. The attenuation coefficient is influenced by the atomic number and density of the material. The u of H2O refers to the linear attenuation coefficient of water, which is used as a reference material for calibrating the Hounsfield scale. Therefore, the Hounsfield value of a pixel is directly related to the u of H2O.

The average photon energy of the primary beam of a CT scanner operating at a tube potential of 120kVp is 70 keV. This is because the average photon energy is approximately equal to two-thirds of the tube potential. Therefore, two-thirds of 120kVp is 80 keV, which is closest to the given answer of 70 keV.

Contrast resolution refers to the ability of a CT scanner to differentiate objects with minimal differences in attenuation coefficients. This means that the scanner can distinguish between tissues or structures that have very similar densities or shades of gray on the CT image. A higher contrast resolution allows for better visualization and distinction of subtle differences in tissue density, which is particularly important in detecting small lesions or abnormalities.

The correct answer is 3 only. This means that the statement "It may be used in conjunction with a multiformat or laser camera" is correct. This suggests that the radiographic film used to archive CT images can be used together with a multiformat or laser camera. The other statements, "It is double emulsion film" and "It is sensitive to ultraviolet light only," are incorrect.

Collimation of the CT x-ray beam is used to limit the detection of scatter radiation, not to increase the intensity of the primary beam. Collimation helps to control the size and shape of the x-ray beam, reducing scatter radiation and improving image quality. By narrowing the beam, collimation focuses the radiation on the desired area, reducing scatter radiation that can degrade the image and increase patient dose. Increasing collimation does not increase the intensity of the primary beam; instead, it restricts the beam to a smaller area.

The answer is 20 lp/cm because a CT scanner's spatial resolution refers to its ability to distinguish small details in an image. lp/cm stands for line pairs per centimeter, which represents the number of pairs of lines that can be distinguished within a centimeter. Therefore, a higher value of lp/cm indicates a higher spatial resolution, meaning that the CT scanner can differentiate smaller details in the image.

The full width at half maximum (FWHM) of a CT scanner refers to the width of the point spread function at half of its maximum intensity. In the context of a CT scanner, spatial resolution is a measure of the scanner's ability to distinguish between small objects or details in an image. A smaller FWHM indicates better spatial resolution, as it means that the scanner can accurately represent smaller structures or features in the image. Therefore, the FWHM of a CT scanner is used to describe its spatial resolution.

Increasing the aperture size of a CT image increases the signal-to-noise ratio. The aperture size refers to the width of the collimator, which determines the amount of X-ray photons that can pass through the patient and reach the detector. By increasing the aperture size, more photons can reach the detector, resulting in a stronger signal. This helps to increase the signal-to-noise ratio, as the signal (desired information) is amplified while the noise (unwanted background information) remains relatively constant. Therefore, increasing the aperture size improves the quality and clarity of the CT image.

The correct answer is 2 and 3. This means that the causes for the poor low contrast resolution of a CT image may include increased electronic noise and decreased patient dose. These factors can contribute to a decrease in image quality and make it difficult to distinguish between different shades of gray in the image.

The average linear attenuation coefficient for water is .206. This means that water absorbs approximately 20.6% of incident radiation as it passes through. This coefficient is used to measure how much radiation is absorbed by a material, and in the case of water, it is relatively high compared to other materials.

During the three dimensional reconstruction of a CT scan, the information included is controlled by the threshold setting. This setting determines the range of pixel values that will be included in the final reconstructed image. By adjusting the threshold, certain structures or densities can be highlighted or excluded, allowing for better visualization and analysis of specific areas of interest. This setting helps in distinguishing between different tissues and structures based on their density levels, thereby enhancing the accuracy and clarity of the reconstructed image.

Retrospective reconstruction of the scan using reduced section spacing and rescanning of the patient using reduced section thickness could both reduce the partial volume effect and provide more accurate CT numbers. By reducing the section thickness and spacing, the images obtained will have a higher spatial resolution, allowing for better differentiation of structures within the renal cyst. This reduces the mixing or averaging of different tissues that can occur with larger section thickness and spacing, resulting in more accurate CT numbers. Therefore, options 2 and 3 are the correct choices.