Computed Tomography Science Flashcards

What is the primary principle behind computed tomography imaging?

Answer: X-ray absorption

Computed tomography (CT) imaging works by sending multiple X-ray beams through the body from different angles. As these X-rays pass through tissues, they are absorbed to varying degrees depending on the tissue density. Detectors then measure the amount of X-rays that pass through, and this absorption data is used to reconstruct cross-sectional images.

Which component of a CT scanner is responsible for rotating the X-ray tube and detector around the patient?

Answer: Gantry

The gantry is the large, donut-shaped component of a CT scanner that houses the X-ray tube and the detectors. It is responsible for rotating these components around the patient to acquire X-ray data from multiple angles. The patient lies on a table that slides through the opening of the gantry during the scan.

In CT imaging, what does the term "slice thickness" refer to?

Answer: The distance between adjacent slices

In CT imaging, 'slice thickness' refers to the thickness of the anatomical cross-section being imaged. However, the question asks about the term in the context of the options, and 'the distance between adjacent slices' is the most accurate description provided for how slices are spaced. This parameter is crucial for ensuring complete coverage of the area of interest and for subsequent 3D reconstructions.

Which type of contrast agent is commonly used in CT imaging to enhance blood vessels and soft tissue?

Answer: Iodinated contrast

Iodinated contrast agents are commonly administered intravenously in CT imaging to enhance the visibility of blood vessels, organs, and soft tissues. Iodine, being a high-atomic-number element, strongly absorbs X-rays, making structures containing it appear brighter on the CT images. This allows for better differentiation of various anatomical structures and pathologies.

What is the Hounsfield unit (HU) scale used for in CT imaging?

Answer: Describing tissue density

The Hounsfield unit (HU) scale is a quantitative scale used in CT imaging to represent the relative density of tissues. Water is assigned a value of 0 HU, air is approximately -1000 HU, and dense bone can be +1000 HU or more. This scale allows radiologists to differentiate between various tissues and pathologies based on their X-ray attenuation properties.

Which imaging technique can provide information about blood flow and perfusion in addition to anatomical details?

Answer: Dynamic CT perfusion

Dynamic CT perfusion is an advanced imaging technique that involves rapidly acquiring multiple CT scans after a contrast agent injection to observe its flow through tissues over time. This allows for the quantification of blood flow, blood volume, and capillary permeability, providing functional information about tissue perfusion in addition to anatomical details. It's particularly useful for assessing stroke or tumor vascularity.

What is the purpose of the CT reconstruction process?

Answer: To convert raw data into an image

The CT reconstruction process is the computational step where the raw X-ray attenuation data, collected by the detectors from multiple angles, is processed by complex algorithms. These algorithms convert the projection data into a cross-sectional image (slice) that can be viewed and interpreted by radiologists. Without reconstruction, the raw data is just a collection of measurements, not an image.

Which type of CT scan is commonly used to assess bone density and diagnose osteoporosis?

Answer: Dual-energy CT

Dual-energy CT (DECT) uses two different X-ray energy spectra simultaneously or sequentially to acquire data. This allows for the differentiation of materials based on their atomic number, making it particularly useful for assessing bone density, characterizing kidney stones, and distinguishing between different tissue types. Its ability to characterize material composition makes it ideal for bone density assessment.

Which type of artifact is caused by high-density materials like metal in the CT scan's field of view?

Answer: Beam-hardening artifact

Beam-hardening artifact occurs when the X-ray beam passes through dense materials, such as metal implants or thick bone. The lower-energy photons in the beam are absorbed more readily, leaving a 'harder' (higher-energy) beam. This causes streaks and dark bands in the image, often appearing between two dense objects or at the edges of very dense objects.

What is the purpose of the CT scout (topogram) image?

Answer: To assist in patient positioning

A CT scout image, also known as a topogram or pilot scan, is a preliminary, low-dose X-ray image taken before the diagnostic CT scan. It provides a frontal or lateral projection of the patient, similar to a conventional X-ray, which is used by the technologist to accurately plan the scan range and position the patient for the subsequent detailed cross-sectional imaging.

Which technique allows for reduced radiation dose in CT imaging while maintaining image quality?

Answer: Low-dose CT

Low-dose CT (LDCT) refers to specific protocols and techniques designed to reduce the amount of radiation exposure to the patient while still maintaining diagnostic image quality. This is achieved through various methods, including adjusting X-ray tube current, voltage, and using iterative reconstruction algorithms. It's particularly important for screening applications like lung cancer screening, where repeated scans might be necessary.

What is the purpose of the CT table's indexing capability?

Answer: To move the patient through the gantry during scanning

The CT table's indexing capability refers to its ability to precisely move the patient incrementally through the gantry opening. This controlled movement allows for the acquisition of sequential slices or a continuous helical scan, ensuring that the entire anatomical region of interest is covered systematically. This precise positioning is critical for accurate imaging and reconstruction.

What is the primary advantage of multislice (multidetector) CT over single-slice CT?

Answer: Faster scan times

Multislice (or multidetector) CT scanners use multiple rows of detectors, allowing them to acquire several slices simultaneously with each rotation of the X-ray tube. This significantly reduces scan times compared to single-slice CT, where only one slice is acquired per rotation. Faster scan times are beneficial for trauma, cardiac imaging, and reducing motion artifacts, especially in uncooperative patients.

What is the term for the phenomenon where a single tissue appears with different densities in different CT images due to varying X-ray attenuation angles?

Answer: Partial volume effect

The partial volume effect occurs when a single voxel (the smallest 3D unit of a CT image) contains more than one type of tissue. The CT number assigned to that voxel will be an average of the attenuation values of all the tissues within it. This can lead to misrepresentation of tissue densities and blurring of small structures, especially when the slice thickness is large relative to the size of the object.

What type of CT imaging is typically used for visualizing blood vessels with high contrast resolution?

Answer: Partial volume effect

The partial volume effect occurs when a structure, such as a small blood vessel, is smaller than the CT voxel size, causing its density to be averaged with surrounding tissues. While not a 'type of CT imaging,' this phenomenon directly impacts the perceived contrast and resolution of small structures. It can make blood vessels appear less distinct, challenging their visualization even when contrast agents are used to enhance them. Understanding and minimizing the partial volume effect is crucial for accurate vascular imaging.

Which factor influences the spatial resolution of a CT scan?

Answer: Slice thickness

Spatial resolution refers to a CT scan's ability to distinguish between two closely spaced objects. Slice thickness directly influences the resolution along the z-axis (the patient's long axis). Thinner slices provide finer detail and better separation of structures in the axial plane, thereby improving the overall spatial resolution. This allows for clearer visualization of small anatomical features and subtle abnormalities.