Computed Tomography Ultimate Flashcards

Which artifact occurs when an object is positioned partially in and partially out of the scan field of view?

Answer: Partial volume artifact

A partial volume artifact occurs when a voxel contains tissues or structures with significantly different attenuation values, such as bone and soft tissue, or when an object is only partially included in the slice thickness. The CT number assigned to that voxel represents an average of these different attenuations, leading to a misrepresentation of the true density and potentially blurring or obscuring small structures.

What is the purpose of using a convolution kernel in CT image reconstruction?

Answer: To improve image quality

Convolution kernels, also known as reconstruction filters, are applied during the image reconstruction process to enhance specific aspects of image quality. Different kernels emphasize either spatial resolution (e.g., sharp or bone kernels) or contrast resolution and noise reduction (e.g., smooth or soft tissue kernels). Choosing the appropriate kernel is crucial for optimizing the image for the specific diagnostic task.

What is the primary purpose of CT fluoroscopy?

Answer: To monitor needle guidance during procedures

CT fluoroscopy provides real-time CT images, similar to conventional fluoroscopy but with cross-sectional views. Its primary purpose is to guide interventional procedures, such as biopsies, drainages, and pain injections, by allowing the operator to continuously monitor the advancement of a needle or catheter. This real-time visualization significantly improves accuracy and safety during these procedures.

Which term refers to the ability of a CT scanner to acquire images in a very short time interval?

Answer: Temporal resolution

Temporal resolution in CT refers to the ability of the scanner to capture images of moving structures with minimal motion blurring, essentially how quickly the data for a single image can be acquired. High temporal resolution is critical for imaging rapidly moving organs like the heart, reducing artifacts caused by cardiac motion or patient breathing. It is often achieved with faster gantry rotation times and multi-detector arrays.

What is the purpose of a CT scout image (localizer) in patient positioning?

Answer: To outline the scanning region

The CT scout image, also known as a localizer or topogram, is a preliminary low-dose X-ray image taken before the diagnostic scan. It serves as a reference image for the technologist to accurately define the anatomical boundaries and precise start and end points for the subsequent diagnostic CT scan. This ensures that the correct area of interest is included in the scan and minimizes unnecessary radiation exposure.

Which term describes the ability of a CT scanner to accurately represent small objects or structures in the images?

Answer: Spatial resolution

Spatial resolution refers to the ability of a CT system to distinguish between two closely spaced objects or to accurately represent small details within an image. High spatial resolution is crucial for visualizing fine anatomical structures like small vessels, bone trabeculae, or tiny lesions. It is influenced by factors such as detector size, focal spot size, and reconstruction algorithms.

Which parameter determines the amount of radiation exposure delivered to the patient during a CT scan?

Answer: Milliampere-seconds (mAs)

Milliampere-seconds (mAs) is a direct determinant of the quantity of X-ray photons produced by the CT tube, and thus directly controls the radiation exposure to the patient. A higher mAs setting results in more X-ray photons, leading to increased patient dose but also reduced image noise. Kilovoltage (kV) also affects dose, but mAs is the primary parameter for controlling the overall photon quantity.

What is the purpose of the CT couch indexing feature?

Answer: To move the patient through the gantry during scanning

The CT couch indexing feature refers to the precise, controlled movement of the patient table (couch) through the gantry during a CT scan. In helical (spiral) CT, the couch moves continuously, while in axial (sequential) CT, it moves in discrete steps between slice acquisitions. This indexing ensures that the entire anatomical region of interest is systematically scanned.

Which factor can contribute to the occurrence of ring artifacts in CT images?

Answer: Detector malfunction

Ring artifacts appear as circular or curvilinear streaks centered on the rotational axis of the CT scanner. They are typically caused by a faulty or miscalibrated detector element in the detector array. If a detector consistently produces incorrect signals, it will manifest as a ring in the reconstructed image because that detector is always at the same radial distance from the center.

What is the purpose of CT dose modulation techniques?

Answer: To optimize radiation exposure

CT dose modulation techniques are advanced features designed to automatically adjust the X-ray tube current (mAs) during a scan based on the patient's anatomy. By reducing the dose in thinner or less attenuating regions and increasing it in thicker or denser areas, these techniques optimize radiation exposure. This maintains image quality while significantly reducing the overall patient dose.

What is the primary advantage of using a higher tube voltage (kV) in CT imaging?

Answer: Improved spatial resolution

Higher tube voltage (kV) increases the energy and penetrating power of the X-ray beam. This reduces beam hardening artifacts, especially in dense tissues, and improves the signal-to-noise ratio. Consequently, it allows for better differentiation of small structures and fine details, leading to improved spatial resolution in the CT image.

What does the term "window width" refer to in CT image analysis?

Answer: Adjusting the display contrast

Window width in CT image analysis refers to the range of Hounsfield units (HU) displayed on the monitor. Adjusting the window width directly controls the contrast of the image. A narrower window width increases the contrast between tissues within that specific range, making subtle differences more visible, while a wider width displays a broader range of tissues with less contrast.

Which type of CT scan is often used for imaging larger areas of the body with minimal patient movement?

Answer: Helical CT

Helical CT, also known as spiral CT, involves continuous rotation of the X-ray tube and detectors while the patient table moves through the gantry. This allows for rapid, continuous acquisition of volumetric data over large anatomical areas. This method minimizes motion artifacts and reduces scan time, making it ideal for imaging extensive body regions with minimal patient movement.

What is the purpose of a CT collimator?

Answer: To shape the X-ray beam

A CT collimator is a device that shapes and restricts the X-ray beam emitted from the tube. Its primary purpose is to define the slice thickness and ensure that only the necessary area is exposed to radiation. This precise beam shaping reduces scatter radiation, improves image quality, and significantly lowers the patient's radiation dose.

Which parameter is adjusted by the kilovoltage (kV) setting in CT scanning?

Answer: Radiation dose

The kilovoltage (kV) setting in CT scanning determines the energy and penetrating power of the X-ray beam. A higher kV setting means the X-rays are more energetic and penetrate tissues more effectively, but it also directly increases the amount of radiation absorbed by the patient. Therefore, kV is a primary parameter for adjusting the radiation dose.