Radiation Detection & X-Ray Tube Components

If insufficient voltage is applied to the electrodes of an ionization chamber, ions will recombine before reaching the electrodes, reducing the current flow.

The negative electrode of an x-ray tube is always called the cathode.

The focal spot of an x-ray tube is located at the anode, where electrons from the cathode collide.

A smaller focal spot reduces the penumbra (blur) in the image, leading to sharper details.

Isotope scans are the most sensitive test for detecting metastatic deposits.

Aortic calcification is diagnosed by fluoroscopy by observing side-to-side movement.

The main disadvantage of third-generation CT scanners is their slower speed compared to later generations.

The second-generation CT scanners' main advantage was a reduction in scanning time.

The first generation of computed tomography used only a single detector.

Each pixel in a CT image stores numerical information in Hounsfield units, which represent the attenuation of the tissue by the x-ray beam.

A single sweep of the x-ray source and detectors around the body during CT is called a projection.

The key development in fourth-generation CT scanners is the stationary detector array.

Each CT projection records the variations in the density and contrast of the tissue being scanned.

CT scanners typically operate on high-frequency voltage generation.

Third-generation CT scanners were the first to use a fan beam that transversed the entire patient at all times.

The z-axis coverage (slab thickness) in a multi-row detector CT scanner is determined by multiplying the detector length by the number of rows.

In a multi-row detector CT scanner, the beam pitch is equal to the detector pitch divided by the number of active detectors (N).

Dual Source CT (DSCT) utilizes two x-ray sources and detector arrays, allowing for double the resolution compared to a single source CT and increasing the speed of data acquisition.

In Dual Source CT, the two x-ray tubes and detectors are positioned with an angular offset of 90 degrees in the gantry.

The degree of x-ray beam attenuation by a material depends on the tissue composition, photon energy level, and how closely the photon energy exceeds the material's K-edge.

The imaging system in CT scanners is responsible for detecting the radiation passing through the cross-section, measuring its intensity, and converting the information into digital data.

The data acquisition system (DAS) converts the information from the imaging system into digital data for processing.

Straton x-ray tubes offer advantages like better heat dissipation, various focal spot sizes, longer tube life, and high-speed volume scanning capabilities.

Straton x-ray tubes can be used in various techniques, including high KV and high mA for prolonged durations, high KV and low mA

Filtration in CT scanners removes long-wavelength x-rays, produces uniform beam hardening, and attenuates the beam for a more uniform distribution.

Straton x-ray tubes allow for high KV and low mA techniques for prolonged durations, enabling longer scanning times without overheating.

Straton x-ray tubes allow for high mAs and short exposure times, enabling faster scans and higher image quality.

Bowtie filters are typically made of Teflon, which is a material with a low atomic number and low density.

Overbeaming refers to an x-ray beam extending beyond the detector, leading to exposure of the patient over a larger area.

Overscanning in spiral CT involves exposing the patient outside the imaged range, especially at the start and end of the scan with multi-row detectors.

Adaptive section collimation technique minimizes overscanning and overbeaming by adjusting the beam width to match the size of the area being scanned.

CT detectors capture the radiation beam from the patient and convert it into electrical signals.

The absorption efficiency of a CT detector is influenced by the atomic number, physical density, size, and thickness of the detector material.

Conversion efficiency refers to the ability of a CT detector to accurately convert the absorbed x-ray signal into an electrical signal.

The efficiency of a CT detector involves capturing, absorbing, and converting x-ray photons into electrical signals.

Response time refers to the speed at which a CT detector can detect an x-ray event and prepare for the next event.

Scintillation detectors convert x-ray energy into light, which is subsequently converted into electrical energy by a photodetector.