Health And Medicine- The CT Registry Review Test

CT numbers are usually provided in the form of Hounsfield units. Hounsfield units are a measurement scale used in computed tomography (CT) imaging to quantify the radiodensity of different tissues. It was developed by Sir Godfrey Hounsfield, who invented the CT scanner. Hounsfield units are based on the linear attenuation coefficient of X-rays passing through a specific tissue compared to that of water. This scale allows for the differentiation of various tissues based on their density, with higher Hounsfield units indicating denser tissues like bone, and lower units indicating less dense tissues like air.

Pixels whose average attenuation coefficients are less than that of water will have negative CT number values. This is because CT numbers represent the relative density of a tissue or material compared to water, with water having a CT number of zero. Since the average attenuation coefficients of these pixels are lower than water, their CT numbers will be negative, indicating that they are less dense than water.

Attenuation refers to the reduction in intensity of an x-ray beam as it interacts with matter. When x-rays pass through a material, they can be absorbed or scattered, causing a decrease in their intensity. This phenomenon is known as attenuation. Scatter and transmission are related to the interaction of x-rays with matter, but they do not specifically refer to the reduction in intensity. Luminescence, on the other hand, is the emission of light from a material, which is not directly related to the reduction in x-ray beam intensity.

Quality control measurements are important in ensuring the accuracy of the calibration of the CT scanner. Performing these measurements on a daily basis allows for frequent checks and adjustments, ensuring that any calibration issues are promptly identified and corrected. This helps maintain the accuracy and reliability of the CT scanner's results, which is crucial for patient diagnosis and treatment.

Xenon is commonly used for gas ionization CT detectors because it has high atomic number and density, which makes it an efficient detector of X-ray photons. It also has a high electron mobility, allowing for fast response times. Additionally, xenon is relatively inert and non-toxic, making it safe for use in medical imaging applications.

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

The optical disk is capable of storing the largest number of CT images compared to the other archival media listed. Optical disks, such as CDs or DVDs, have a higher storage capacity than floppy disks, magnetic tapes, or VHS tapes. They can store large amounts of data, including high-resolution CT images, making them an ideal choice for archiving and storing a large number of images.

Overlapping scans with narrow section thickness would greatly improve the quality of CT studies requiring multiplanar reformats. This is because overlapping scans allow for better coverage of the area of interest, ensuring that no information is missed. Narrow section thickness means that the slices obtained are thinner, resulting in higher resolution and better visualization of structures. By combining these two parameters, the resulting images will have improved clarity, detail, and accuracy, making them ideal for multiplanar reformats.

A pixel is commonly defined as a picture element. It refers to the smallest unit of a digital image or display that can be individually controlled. Each pixel represents a specific color or shade, and when combined with other pixels, forms the complete image.

(b) The use of a fan shaped beam during CT imaging increases the total volume of tissue irradiated, thereby increasing the amount of scatter radiation produced.

Misregistration refers to the loss of anatomic information between contiguous sections caused by inconsistent patient breathing. This occurs when the sections of an image are not properly aligned due to variations in breath-holding or breathing patterns during the scanning process. As a result, there may be a mismatch or misalignment between the different sections, leading to a loss of anatomical continuity and potentially affecting the accuracy of the diagnosis.

A voxel is a term used in computer graphics and imaging to describe a three-dimensional volume element. It represents a small cube or cuboid within a larger three-dimensional space. Unlike a pixel, which represents a single point in a two-dimensional image, a voxel represents a small volume within a three-dimensional object or scene. Therefore, the correct answer is "a volume element".

The portion of the primary beam interacting with a single detector is known as a "ray". A ray refers to a narrow beam of light or radiation that travels in a straight line. In the context of this question, it specifically represents the part of the primary beam that interacts with a detector, which is responsible for capturing the image or data. The other options, such as "view," "profile," and "sample," do not accurately describe the specific interaction between the primary beam and the detector.

Most modern CT scanners use the filtered back-projection method for reconstruction. This method involves passing the raw data through a filter to remove unwanted high-frequency noise and then back-projecting the filtered data onto a 2D or 3D image. This technique helps to improve image quality and reduce artifacts in the reconstructed images. It is widely used in modern CT scanners due to its efficiency and ability to produce high-quality images.

Blood +42 to +58

Good patient - technologist communication is the best method to reduce respiratory motion on the CT image. By instructing the patient to hold their breath or breathe in a specific pattern during the scan, the technologist can minimize motion artifacts and obtain clearer images. This communication allows the technologist to coordinate with the patient and capture the images at the optimal moment, reducing the impact of respiratory motion on the CT image. The other options, such as reduced scan times, use of immobilization devices, and glucagon administration, may have their own benefits but are not specifically targeted at reducing respiratory motion.

Thermionic emission is the process by which electrons are produced at the cathode of a CT x-ray tube. This occurs when the cathode is heated, causing the electrons to gain enough energy to overcome the work function and be emitted into the vacuum. The emitted electrons are then accelerated towards the anode, creating the x-ray beam used in imaging. Rectification refers to the conversion of alternating current (AC) to direct current (DC), anode heel effect refers to the uneven distribution of x-rays produced in the x-ray tube, and isotropic emission refers to the emission of x-rays in all directions.

A first generation CT scanner consists of an x-ray tube and two detectors that translate across the patient's head while rotating. The rotation is done in 1 degree increments. The question asks for the total rotation, so we need to add up all the increments. Since each increment is 1 degree and the rotation is done in a full circle, the total rotation is 360 degrees. However, the question specifically asks for the rotation "across the patient's head," which suggests that only half of the rotation is being considered. Therefore, the correct answer is 180 degrees.

The spatial resolution along the z axis is decreased when the pitch is increased. An increase in pitch causes less information to e acquired for each section reconstructed. This increase in pitch broadens the section sensitivity profile and reduces the spatial resolution.

First generation CT Scanners acquired data through a process based on a principle of tube translation and rotation around a patients head.

Areas of a CT image that contain minimal changes in tissue density are represented by low spatial frequencies. This is because low spatial frequencies correspond to large-scale variations in tissue density, while high spatial frequencies correspond to small-scale variations. In areas with minimal changes in tissue density, such as homogeneous regions or large structures, there are fewer small-scale variations, resulting in low spatial frequencies. Therefore, low spatial frequencies are used to electronically represent these areas in a CT image.

Magnetic tape and magnetic optical disk may be used for the archival storage of CT images. Magnetic tape is a traditional storage medium that offers high capacity and long-term durability. Magnetic optical disk, on the other hand, combines the advantages of both magnetic and optical storage technologies, providing a reliable and secure option for long-term storage of medical images.

The kernel does not affect the dimensions of a voxel. The dimensions of a voxel are determined by factors such as slice thickness, matrix size, and DFOV. The kernel, on the other hand, is a mathematical function used in image reconstruction to smooth or sharpen the image. It does not directly impact the size or dimensions of the voxel.

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

Ring artifacts on a CT image are associated with the rotate-rotate tube-detector geometric relationship. This means that both the X-ray tube and the detector rotate around the patient simultaneously. These artifacts occur due to inconsistencies in the detector response, resulting in rings or circular patterns on the image.

Linearity is the term used to describe the relation between the linear attenuation coefficients of an object and the calculated CT numbers. In CT imaging, the linear attenuation coefficient represents how much the X-ray beam is attenuated as it passes through different tissues. The CT numbers are calculated based on these attenuation coefficients and are used to assign different shades of gray to different tissues in the CT image. Therefore, linearity refers to the linear relationship between the attenuation coefficients and the CT numbers, ensuring accurate representation of tissue densities in the image.

(d) The dimension of a pixel may be calculated by dividing the field of view by the matrix size.

Both postpatient collimation and predetector collimation reduce scatter radiation reaching the detectors. Postpatient collimation refers to the process of limiting the size of the X-ray beam after it has passed through the patient, which helps to reduce scatter radiation. Predetector collimation, on the other hand, refers to the process of limiting the size of the X-ray beam before it reaches the detectors, further reducing scatter radiation. Therefore, both A (postpatient collimation) and C (predetector collimation) are correct answers as they both contribute to reducing scatter radiation.

A byte in the binary number system is a series of 8 bits of information. Bits are the basic units of information in the binary system, and a byte consists of 8 of these bits. Each bit can have a value of either 0 or 1, allowing for a total of 256 (2^8) different combinations or possible values within a byte. Therefore, the correct answer is 8.

A CT image is formed by projecting back all of the attenuation values recorded during data acquisition onto a matrix. The matrix is a two-dimensional grid that represents the image, with each element of the matrix corresponding to a specific pixel in the image. By assigning attenuation values to each pixel in the matrix, the CT image is created, allowing for visualization of the internal structures of the scanned object.

(b) The contrast of a CT image is controlled by the spatial frequencies of the tissues within the section.

The primary interaction between x-ray photons and tissue during CT examinations 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 in a different direction and lose some of its energy. This interaction is important in CT imaging as it contributes to the formation of the final image by providing information about the density and composition of the tissue being imaged.

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 in the scanner, which is responsible for capturing the x-ray signals and converting them into an image. This malfunction could result in a straight line artifact appearing on the scanogram.

Silver halide is not commonly used as a CT scintillation detector material. CT scintillation detectors are typically made of materials such as ceramic rare earth, bismuth germinate, and cadmium tungstate. These materials have high atomic numbers and are efficient at converting X-ray photons into visible light, which can then be detected by the scintillation detector. Silver halide, on the other hand, is commonly used in photographic film but not as a scintillation detector material.

(d) The array processor is a specialized component of the CT computer system. It is capable of performing the massive calculations required for CT image reconstruction.

(b) The spatial resolution of a CT examination can be improved with the use of small focal spots, narrow sections, and large matrices

In 1917, the Austrian mathematician Radon proved that it was possible to reconstruct a three-dimensional object from the infinite set of all of its projections.

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.

Partial volume averaging refers to the blurring or loss of detail in an image due to the mixing of different tissue types within a voxel. When the slice thickness is decreased, the voxel size becomes smaller, allowing for better differentiation between different tissues. This reduces the chances of mixing different tissues together and decreases the effect of partial volume averaging. Therefore, decreasing the slice thickness is the correct answer as it helps to minimize partial volume averaging on the CT image.

CT produces diagnostic images with improved low-contrast resolution compared to conventional radiography. This means that CT scans are able to detect and distinguish subtle differences in contrast between tissues, allowing for better visualization of structures with similar densities. This is particularly useful in identifying small lesions or abnormalities that may not be easily seen on conventional radiographs.

Beam hardening occurs as the x-ray beam traverses the patient. The x-ray beam used in CT is composed of x-ray photons with numerouse different energy levels. The heterogeneous beam undergoes an increase in average photon energy as it passes through the patient and the lower energy hpotons are absorbed.

The 3 terms can be used interchangably.

Fourth-generation CT scanners use a rotate-stationary tube-detector configuration. This means that while the detector remains stationary, the X-ray tube rotates around the patient to capture images from different angles. This configuration allows for faster scanning times and improved image quality compared to previous generations.

Statistical noise is the most common type of noise found in CT images. This type of noise is caused by random variations in the number of x-ray photons detected by the CT scanner. It can result in a grainy appearance in the image and can affect the overall image quality. Statistical noise can be reduced by increasing the number of x-ray photons used during the imaging process or by using advanced image reconstruction techniques.

(b) Retrospective reconstruction uses scan or "raw" data to change the matrix, DFOV, center, and algorithm used for a CT image. The slice thickness and SFOV are specifically used for data acquistion and cannot be altered retrospectively.

(c) The analytic methods of CT image reconstruction include the filtered back-projection and the Fourier transform method. These techniques are called analytic because they use precise formulas for image reconstruction.

The correct answer is noise. In medical imaging, noise refers to the random variation in pixel values that can occur due to various factors such as electronic interference, statistical limitations, or other sources of error. This variation can cause fluctuations in CT numbers, especially in images of uniform and homogeneous materials. Noise can affect image quality by reducing the clarity and sharpness of the image, and it is important to minimize noise levels to improve diagnostic accuracy.

Interpolation is a mathematical technique used exclusively for image reconstruction with spiral CT scanners. It involves estimating pixel values based on surrounding known data points. In the context of CT scanners, interpolation is used to fill in the gaps between acquired data points to create a complete image. This is necessary because spiral CT scanners acquire data in a helical pattern, resulting in unevenly spaced data points. Interpolation helps to create a smooth and continuous image from these irregularly spaced data points.

A CT scanner is a medical imaging device that uses X-rays to produce detailed cross-sectional images of the body. Spatial resolution refers to the ability to distinguish small details in an image. In this context, lp/cm stands for line pairs per centimeter, which is a measure of spatial resolution. The higher the lp/cm value, the better the spatial resolution. Therefore, an accurate and modern CT scanner is capable of a spatial resolution of up to 20 lp/cm, meaning it can distinguish small details with high precision.

The SFOV size is determined by the number of detectors activated during data acquisition.