Computed Tomography (CT) Flashcards

X-rays of the body are captured from various angles during computed tomography (CT), which produces images that resemble 2- and 3-dimensional slices (cross-sections). All jewelry and metal objects, such as zippers and belt buckles close to the body portion being scanned, should be taken off by anyone getting a CT scan. Why are patients asked to remove metal before a CT scan?

Answer: The items may block the x-rays and blur the images

Agile Methodology is characterized by its iterative and incremental approach, focusing on flexibility, collaboration, and rapid delivery. It breaks down projects into small, manageable iterations (sprints) to allow for quick progressions and faster releases of working software. This enables teams to adapt to changing requirements and deliver value continuously.

A radiopaque contrast agent, a material that can be seen on X-rays to aid in identifying one tissue from another, may be administered to patients before a CT scan. Which of the following contrast agents is used with CT the most frequently?

Answer: Iodine

Metal objects, such as jewelry and zippers, are radiopaque, meaning they absorb X-rays. During a CT scan, these items can block the X-ray beam, creating artifacts or streaks on the images. These artifacts can obscure important anatomical structures, making it difficult for radiologists to accurately interpret the scan results and potentially leading to misdiagnosis.

Using CT and a radiopaque contrast agent, CT angiography creates 2- and 3-dimensional pictures of blood vessels to look for anomalies. Which of the following statements most accurately describes why CT angiography is frequently employed instead of traditional angiography?

Answer: Is less invasive

Iodine-based contrast agents are the most frequently used with CT scans due to their high atomic number, which allows them to effectively absorb X-rays and enhance the visibility of blood vessels and soft tissues. They are typically administered intravenously to highlight specific structures and differentiate them from surrounding tissues. Other agents like barium are used for gastrointestinal imaging, while gadolinium is primarily for MRI.

What kind of detector is used now that is both effective and popular?

Answer: Solid state crystalline detectors

CT angiography is frequently preferred over traditional angiography because it is a significantly less invasive procedure. Traditional angiography involves inserting a catheter directly into an artery, which carries higher risks such as bleeding, infection, and arterial damage. CT angiography, on the other hand, only requires an intravenous injection of contrast material, making it safer and more comfortable for the patient.

What part of the CT gantry measures photons that are transmitted and pass through the patient?

Answer: Detectors

Solid state crystalline detectors, such as those made from cadmium tungstate or ceramic scintillators, are widely used in modern CT scanners. They are highly efficient at converting X-ray photons into light, which is then converted into electrical signals. Their high efficiency and fast response times contribute to improved image quality and reduced patient radiation dose.

What procedure results in a more monochromatic beam and lowers patient radiation exposure by reducing the longest wavelength photons?

Answer: Filtration

Detectors are the critical components within the CT gantry that measure the X-ray photons that have passed through the patient's body. These detectors convert the transmitted X-ray energy into electrical signals, which are then processed by a computer to reconstruct the cross-sectional images. The number and arrangement of detectors directly impact image quality and scan speed.

For what group have weight-based CT protocols with color-coding been established to help lower patient doses?

Answer: Pediatric

Filtration in CT imaging involves placing thin sheets of metal (like aluminum or copper) in the X-ray beam path. This process selectively absorbs lower-energy, longer-wavelength photons, which contribute more to patient dose without significantly improving image quality. By removing these 'soft' X-rays, filtration results in a more monochromatic and higher-energy beam, reducing patient radiation exposure and improving image quality through a process known as beam hardening.

What is the fundamental principle behind Computed Tomography (CT) imaging?

Answer: X-ray absorption

Pediatric patients are particularly sensitive to radiation, making dose reduction a critical concern in CT imaging for this group. Weight-based CT protocols with color-coding have been established to help tailor the radiation dose precisely to the child's size. This ensures that the lowest possible radiation dose is used while still obtaining diagnostic-quality images, minimizing potential long-term risks.

Which of the following is an advantage of CT over conventional X-ray imaging?

Answer: Better soft tissue contrast

The fundamental principle behind Computed Tomography (CT) imaging is X-ray absorption. A CT scanner uses an X-ray tube to generate X-rays that pass through the patient's body, and detectors measure the amount of X-rays absorbed by different tissues. The varying absorption rates, based on tissue density, allow a computer to reconstruct detailed cross-sectional images.

What does the term "slice thickness" refer to in CT imaging?

Answer: The spacing between slices

One significant advantage of CT over conventional X-ray imaging is its superior ability to differentiate between various soft tissues. While conventional X-rays provide a 2D projection, CT creates detailed cross-sectional images that clearly distinguish structures like organs, muscles, and fat based on their different X-ray absorption properties. This enhanced contrast is crucial for diagnosing a wide range of conditions.

Which component of a CT scanner rotates around the patient during image acquisition?

Answer: Gantry

In CT imaging, 'slice thickness' refers to the width of the individual cross-sectional images acquired by the scanner. It essentially defines the dimension of the tissue volume represented by each image. While it can influence the detail within a single slice, it more accurately describes the spacing or thickness of the anatomical section being imaged.

In CT imaging, what is a "Hounsfield Unit" (HU) a measure of?

Answer: Tissue density

The gantry is the large, donut-shaped component of a CT scanner that houses the X-ray tube and the detector array. During image acquisition, the gantry rotates rapidly around the patient, allowing the X-ray tube to emit radiation from multiple angles and the detectors to capture the transmitted X-rays. This rotation is essential for collecting the data needed to reconstruct cross-sectional images.

Which type of contrast medium is often used in CT imaging to enhance visualization of blood vessels and other structures?

Answer: Iodine-based

A Hounsfield Unit (HU) is a quantitative scale used in CT imaging to measure the radiodensity of tissues. It is a standardized unit that relates the attenuation coefficient of a tissue to that of water, which is assigned a value of 0 HU. Different tissues have characteristic HU values, allowing radiologists to differentiate between structures like bone, soft tissue, fat, and air.

Which CT imaging technique provides detailed information about blood flow and perfusion in tissues?

Answer: Perfusion CT

Iodine-based contrast media are commonly used in CT imaging to enhance the visualization of blood vessels and other highly vascularized structures. When injected intravenously, the iodine temporarily increases the radiodensity of blood, making arteries, veins, and organs appear brighter on the CT images. This helps in detecting abnormalities like tumors, aneurysms, and blockages.

Which type of CT scan is specifically designed for imaging the coronary arteries and assessing heart health?

Answer: Cardiac CT

Perfusion CT is a specialized CT imaging technique that provides dynamic information about blood flow and perfusion in tissues. By rapidly acquiring multiple images after contrast injection, it can quantify parameters such as cerebral blood flow (CBF), cerebral blood volume (CBV), and mean transit time (MTT). This technique is particularly valuable for assessing stroke, tumors, and other conditions affecting tissue viability.

What is the purpose of a CT scout image?

Answer: To measure bone density

Cardiac CT is a specialized type of CT scan specifically designed to image the coronary arteries and assess heart health. It uses advanced technology to capture detailed images of the heart's anatomy, identify blockages or narrowing in the coronary arteries (coronary artery disease), and evaluate cardiac function. This non-invasive procedure is crucial for diagnosing and managing heart conditions.