CT Physics 2 Hhh

The correct answer is 0.5 and 1.2 mm. This range represents the filament sizes for modern CT x-ray tubes. The filament size is important in determining the resolution and image quality of the CT scan. A smaller filament size allows for better spatial resolution and improved image detail. On the other hand, a larger filament size may result in decreased resolution and poorer image quality. Therefore, the range of 0.5 and 1.2 mm is considered optimal for modern CT x-ray tubes.

A collimator is not a part of the CT tube. The CT tube consists of a tungsten target, rotating anode, and filament. The tungsten target generates the x-rays, the rotating anode allows for continuous x-ray production, and the filament heats up and releases electrons to create the x-rays. The collimator, on the other hand, is a separate component that is used to control the size and shape of the x-ray beam. It helps to limit the radiation exposure to the patient and improve image quality by reducing scatter radiation.

The unit mGy-cm (milligrays per centimeter) is used to express the total patient dose from helically acquired CT examination. This unit combines the measurement of absorbed dose (in milligrays) with the measurement of distance (in centimeters) to represent the total dose received by the patient during the CT scan. The other options, such as roentgens (R), curies, and R-cm, are not commonly used to express the total patient dose in CT examinations.

Osmolality refers to the number of ions formed when a substance dissociates in a solution. It is used to determine the biologic effect of iodinated contrast media. Osmolality is a measure of the concentration of solute particles per kilogram of solvent, and it helps to assess the osmotic pressure exerted by the contrast media in the body. By measuring osmolality, healthcare professionals can determine the potential impact of the contrast media on the osmotic balance and potential adverse effects on the body.

The correct answer is 1, 2, and 3. During the reconstruction of a CT image, mathematical manipulations are required. These manipulations are accomplished using an algorithm, a kernel, and a mathematical filter function.

A non-ionic contrast material is described as one that does not dissociate into charged particles in solution. This means that it does not carry an electrical charge when dissolved in a solution. This is in contrast to an ionic contrast material, which does dissociate into charged particles when dissolved. The term "non-ionic" refers to the lack of electrical charge, making it a suitable choice for certain medical procedures where the presence of charged particles could interfere with the desired outcome.

When an image is reconstructed a second time with some change in technical factors, it is referred to as "retrospective." This term implies that the reconstruction is being done retrospectively, or after the initial reconstruction, with alterations to the technical parameters. It suggests a retrospective analysis or adjustment of the image based on new information or requirements. The other options, "reiterated," "post-processed," and "reformatted," do not specifically convey the notion of a second reconstruction with technical changes.

The correct answer is stochastic. Stochastic refers to a random or probabilistic relationship between radiation exposure and its harmful effects. This means that the effects of radiation exposure cannot be predicted with certainty, as they depend on chance and probability. Stochastic effects include the development of cancer, genetic mutations, and other long-term health risks.

An intrathecal injection is a procedure where contrast material is injected directly into the subarachnoid space, which is the space between the arachnoid membrane and the pia mater in the spinal cord. This injection allows for better visualization of the spinal cord and nerve roots during a CT examination of the lumbar spine. The subarachnoid space is the most appropriate location for the injection as it provides optimal distribution of the contrast material for accurate imaging. The other options, such as the dura mater, vertebral foramen, and subdural space, are not the correct locations for the injection in this context.

Urticaria refers to hives, which are raised, itchy, and red bumps on the skin. This condition is characterized by an allergic reaction, often triggered by certain foods, medications, or environmental factors. Severe nausea with associated vomiting, urinary tract infection, and bronchospasm are unrelated to urticaria and do not describe its symptoms or characteristics.

The bolus technique provides the greatest overall plasma iodine concentration among the given options. In this method, a large volume of contrast agent is injected rapidly into the bloodstream, resulting in a high concentration of iodine in the plasma. This allows for better visualization of blood vessels and organs during imaging procedures, such as CT scans. Drip infusion involves a slow and continuous administration of the contrast agent, while the biphasic technique involves both a rapid injection and a subsequent slower infusion. CT portography is a specific imaging technique that uses contrast agent to visualize the portal venous system.

The major disadvantage of the back-projection method of image reconstruction is the appearance of star artifacts. Star artifacts are unwanted bright streaks or spokes radiating from high-contrast objects in the image. These artifacts are caused by the incomplete sampling of the Fourier space during the reconstruction process, leading to inaccurate representation of high-frequency information. The star artifacts can degrade the image quality and make it difficult to interpret the reconstructed image accurately.

Beam hardening is the correct answer because it refers to the phenomenon where the x-ray beam becomes more energetic as it passes through an object, causing the lower energy photons to be absorbed more than the higher energy ones. This leads to a change in the overall energy spectrum of the x-ray beam, resulting in artifacts such as streaks or dark bands in the image.

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 reduce scatter radiation and improve image quality by narrowing the x-ray beam to only the necessary area of interest. Increasing collimation would result in a narrower beam, which reduces scatter radiation but does not affect the intensity of the primary beam.

The correct answer is 1,2,3. When choosing a scan field of view, the CT technologist is controlling the diameter of data acquisition, the number of activated detectors within the array, and correction factors for the specific area of anatomic interest. These factors determine the extent of the scan and the amount of data acquired during the scan.

The effective dose is a relative radiation dose measurement term that takes into account the tissue radiosensitivity. This means that it considers the varying sensitivity of different tissues to radiation. Some tissues are more sensitive to radiation and can be more easily damaged, while others are more resistant. Therefore, the effective dose calculation takes into consideration the potential harm that radiation can cause to different tissues, allowing for a more accurate assessment of the overall radiation dose received by an individual.

kVp stands for kilovolt peak, which is a measure of the peak voltage of the X-ray beam used in CT scanning. The higher the kVp, the greater the penetration of the X-ray beam through the object being scanned. This increased penetration reduces the attenuation of the X-ray beam, resulting in less absorption and scattering by the object. Therefore, kVp can affect the attenuation of an object during CT data acquisition.

A saline flush immediately following the IV administration of iodinated contrast material has several advantages. Firstly, it can help reduce the required dose of contrast agent, which can be beneficial for patients with renal impairment or those who are at a higher risk of adverse reactions. Secondly, it can reduce the incidence of contrast-induced nephrotoxicity (CIN), a condition where the contrast agent can cause kidney damage. Lastly, it can help reduce streaking artifacts that may occur from the dense contrast agent in the vasculature, improving the quality of the imaging results.

As the reconstruction field of view (FOV) increases, more data needs to be acquired and processed, resulting in an increase in patient dose. This is because a larger FOV requires more X-ray exposures to cover the entire area, leading to increased radiation exposure for the patient.

As the slice thickness increases, the patient dose decreases. This is because a thicker slice requires fewer X-ray exposures compared to a thinner slice to cover the same distance of coverage. Therefore, the patient is exposed to less radiation when a thicker slice is used, resulting in a decrease in patient dose.

Decreasing the tube rotation from 360 to 180 degrees would serve to decrease patient radiation dose during a CT examination. This is because reducing the tube rotation angle means that fewer X-ray beams are emitted, resulting in a lower radiation dose to the patient.

CT systems are not limited to non-oblique transverse scanning, as they can also generate oblique images. They can generate straight coronal or sagittal images, so statement 2 is false. However, CT systems do have moving parts, such as the rotating gantry and the patient table, so statement 3 is also false. Therefore, the correct answer is 1 2 3.

On a single-row detector scanner, the thickness of the image reconstructed from a helical scan is equal to the beam collimation. This means that the thickness of the slice in the reconstructed image will be the same as the width of the x-ray beam used during the scan.

Binning is the correct answer because it refers to the process of combining signals from adjacent detectors in a computed tomography (CT) scan to form an image. This technique helps to improve the image quality and reduce noise by increasing the signal-to-noise ratio. Binning involves summing the signals from neighboring detectors and assigning the combined value to a single pixel in the image. This process helps to enhance the spatial resolution and overall image clarity in CT imaging.

When applying a sharp or high-pass reconstruction filter during the image reconstruction of CT raw data, an increase in contrast resolution does not occur in the resulting images. Contrast resolution refers to the ability of an imaging system to distinguish between objects with similar densities. In this case, the sharp or high-pass reconstruction filter is primarily used to enhance the edges of structures in the image, resulting in improved edge enhancement. However, it does not directly affect the contrast resolution, which is the ability to differentiate between subtle differences in density. Therefore, an increase in contrast resolution does not occur when applying this type of filter.

MDCT scanners capable of collecting 64 slices in a single rotation do not use filtered back projection as their method of image reconstruction. Filtered back projection is an older technique that reconstructs images by projecting the data onto a two-dimensional plane. However, MDCT scanners with 64 slices use more advanced methods such as iterative reconstruction, which improves image quality and reduces artifacts by iteratively refining the image based on mathematical algorithms.

The correct answer is "1 and 2". The 18-gauge and 20-gauge angiocatheter sizes may be safely used for the automated power injection of iodinated contrast agents at flow rates higher than 3mL/sec. This means that these two sizes are able to handle the higher flow rates without causing any complications or issues during the injection process. The 22-gauge angiocatheter size is not suitable for flow rates higher than 3mL/sec and may not be able to handle the increased pressure and volume of the contrast agent.

The geometric efficiency of a CT detector is primarily influenced by the amount of interspace material between detectors. This is because the interspace material can cause scattering of the X-ray photons, leading to a decrease in the efficiency of the detector in capturing the photons. Therefore, minimizing the amount of interspace material between detectors can improve the geometric efficiency of the CT detector. The other factors mentioned (atomic number of the detector material, size of the detector element, and size of the tube filament) may have some influence on image quality or sensitivity, but they are not the primary factors affecting the geometric efficiency.

The volume of each voxel can be calculated by multiplying the section width by the pixel size. In this case, the section width is given as 1.25 mm and the pixel size can be calculated by dividing the DFOV (38 cm) by the matrix size (512). Converting the DFOV to mm (38 cm = 380 mm), the pixel size is 380 mm / 512 = 0.74 mm. Multiplying the section width (1.25 mm) by the pixel size (0.74 mm) gives us a volume of 0.925 mm^3. Therefore, the correct answer is 0.93mm.

The limiting resolution is determined at a point where the signal frequency corresponding to a particular object has reached 10%. This means that the resolution of the system is limited and cannot accurately distinguish between two points on the object that are closer than 10% of the signal frequency. In other words, the system is only able to resolve details on the object that are larger than 10% of the signal frequency.

MIP images, or Maximum Intensity Projection images, are commonly used for visualizing air-filled spaces in medical imaging. However, they have a limitation in that they do not demonstrate detail beneath the brightest pixel. This means that if there is a bright area in the image, such as a bone or a dense structure, the MIP image will not show any details beyond that point. This is important to keep in mind when interpreting MIP images, as it may lead to a lack of information in certain areas of the image.

Enteric precautions are specifically designed to protect against infection transmitted through fecal material. Enteric refers to the intestines, and enteric precautions involve measures such as proper hand hygiene, wearing gloves, using dedicated equipment, and maintaining proper sanitation to prevent the spread of pathogens found in feces. This type of isolation technique is important in healthcare settings to prevent the transmission of diseases such as Clostridium difficile (C. diff) and norovirus, which can be spread through contaminated fecal matter.

The range of serum iodine concentration for adequate tissue opacification during contrast-enhanced CT examinations is 2-8mg/ml. This range ensures that the iodine-based contrast agent is present in sufficient concentration in the bloodstream to provide clear visualization of the tissues and organs during the CT scan. Higher concentrations may lead to overexposure and potential side effects, while lower concentrations may result in inadequate opacification and poor image quality. Therefore, the ideal range for adequate tissue opacification is 2-8mg/ml.

The streaking artifact that occurs in the area of the posterior fossa during a CT examination of the brain is referred to as the Hounsfield bar. The Hounsfield bar is a term used to describe streaking artifacts caused by beam hardening, which is a phenomenon that occurs when the X-ray beam passing through different tissues gets attenuated differently. This causes streaks of high density in the image, which appear as a bar-like artifact in the posterior fossa region.

The mathematical process that allows MDCT images to be reconstructed at any point along the acquired volume is commonly referred to as z-filtering. Z-filtering is a technique used in computed tomography (CT) imaging to selectively filter the data along the z-axis, which represents the patient's body. This filtering process helps to remove artifacts and noise, resulting in clearer and more accurate reconstructed images. It is an essential step in the reconstruction process of MDCT images.

The correct answer is 3D shaded surface display. In this technique, tissues other than the surface of a structure are excluded by setting a threshold value and eliminating pixels above or below that threshold. This allows for the creation of a 3D representation of the surface of the structure, with shading applied to enhance the visualization of the surface contours.

The product of the selected mA setting and the scan time is called constant mAs. This term refers to the consistent product of these two variables during the entire duration of the CT x-ray exposure. It is used to determine the total radiation dose delivered to the patient during the scan.

In MSCT (Multislice Computed Tomography) imaging, scatter radiation refers to the unwanted scattered photons that can degrade the quality of the image. By utilizing a high-resolution comb, the MSCT detector array aims to reduce scatter radiation. This comb helps in blocking or absorbing the scattered photons, allowing only the desired primary photons to reach the detector. This ultimately improves the image quality by reducing noise and increasing the clarity of the scanned area.

Perspective volume rendering is the correct answer because it is a 3D imaging technique commonly used in CT colonography to provide "fly-through" images. This technique utilizes a perspective projection to create realistic images that simulate the experience of flying through the colon. It takes into account the viewer's position and angle, allowing for a more immersive and accurate visualization of the colon.

The volume data, from which the 3D SSD is generated, is not created by combining transverse, sagittal, and coronal reconstructions. This statement is false because 3D SSD (shaded surface display) is a technique used to create a three-dimensional representation of an object or structure from volumetric data. The volume data is obtained directly from the CT scan and does not require combining different reconstructions.

Linearity refers to the ability of a system to produce output that is directly proportional to the input. In the context of image quality, linearity refers to the accuracy of the system in reproducing different shades of gray. Daily air or water calibration is performed to evaluate linearity by ensuring that the system is producing consistent and accurate gray levels throughout the image. This helps in maintaining the quality and reliability of the images produced by the system.

CTDI w stands for Computed Tomography Dose Index weighted. It is a radiation dose index calculation that takes into account the variations in absorption across the field of view due to beam hardening. This means that it considers how different tissues absorb radiation differently, resulting in a more accurate assessment of the radiation dose delivered during a CT scan. CTDI w is an important parameter in evaluating and optimizing radiation dose in CT imaging.

The correct answer is 1 and 2. Compared with single-slice CT, patient radiation dose during a multidetector CT study may be higher because of the use of a cone beam of radiation and acquisitions at thinner section widths. The cone beam of radiation used in multidetector CT scans covers a larger area of the patient's body, resulting in a higher radiation dose. Additionally, thinner section widths allow for more detailed imaging but also increase the radiation dose as more slices need to be acquired.

When reconstructing a set of images, the DFO (Detector Field of View) determines the size of the image. A larger DFO results in a larger image, while a smaller DFO results in a smaller image. In this case, the second set of images has a larger DFO (300 mm) compared to the first set (150 mm). Therefore, the second set of images will have a better resolution since it covers a larger area. Additionally, since the second set has a larger DFO, it will also have more pronounced noise compared to the first set. Finally, since the first set has a smaller DFO, it requires more radiation exposure to cover the same area, resulting in a higher patient dose. Therefore, the correct answer is 1, 2, and 3.

The International Normalized Ratio (INR) is calculated to standardize the prothrombin time (PT), which measures the time it takes for blood to clot. By standardizing the PT, the INR allows for consistent interpretation of clotting times across different laboratories and testing methods. This is important for monitoring patients on anticoagulant therapy, such as those taking warfarin, to ensure their blood is clotting within the desired range to prevent bleeding or clotting disorders.

When fast-moving electrons collide with matter, they lose kinetic energy. This lost energy is then converted into the emission of an x-ray photon. Therefore, the correct answer is 2 only.

The correct answer is 3 only because dehydration is a known risk factor for contrast-induced nephrotoxicity (CIN). Pheochromocytoma and allergy to shellfish are not directly related to CIN.

The FDK algorithm is a reconstruction technique used in computed tomography (CT) imaging. It is used to overcome image artifacts caused by various factors such as patient motion, beam hardening, partial volume averaging, and beam divergence. Beam divergence refers to the spreading out of the X-ray beam as it travels from the X-ray source to the detectors. This can lead to blurring and loss of image resolution. By applying the FDK algorithm to CT acquisition data, the effects of beam divergence can be minimized, resulting in improved image quality.

The intensity of the laser beam in a laser camera is determined by the pixel values in the image data. The pixel values represent the brightness or darkness of each pixel in the image, and they can be used to control the intensity of the laser beam. The intensifying grid and magnifying power of the lens may affect other aspects of the image, but they do not directly determine the intensity of the laser beam.

When the reconstruction FOV is decreased, the spatial resolution is not increased. The spatial resolution refers to the ability of an imaging system to distinguish between two closely spaced objects. When the FOV is decreased, the system is capturing a smaller area, resulting in fewer details being captured and therefore a decrease in spatial resolution. The pixel size, on the other hand, is increased when the FOV is decreased, as the same area is now represented by a smaller number of pixels. Additionally, noise in the image is also increased when the FOV is decreased, as the smaller area being captured has a higher likelihood of containing random variations or artifacts.

In the formula used to calculate the linear attenuation coefficient, the symbol Io represents the incident intensity. The incident intensity refers to the initial intensity of the radiation before it interacts with the absorber. It is the intensity of the radiation beam that is directed towards the absorber. The equation calculates the transmitted intensity (I) after it passes through the absorber, using the incident intensity (Io), the absorber thickness (x), and the linear attenuation coefficient (u).