CT

FeaturedImage FBP

Filtered BackProjection (FBP) Illustrated Guide for Radiologic Technologists

The Filtered BackProjection (FBP) algorithm is the basis for image reconstruction (converting from the measured data to the image) on modern CT scanners. FBP is a fast and direct method to generate CT images. As the name suggests it is composed of two main steps filtering the data (along the row direction in the detector) …

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ctScanModes 400

Illustrated comparison of CT Scan Modes [axial, helical, wide-cone axial, low pitch, high pitch] for Radiologic Technologists

CT (Computed Tomography) scanning can be accomplished with multiple different scan modes which have different characteristics. Axial non-volumetric scanning is how CT began where one (or just a few) slices are acquired during each gantry rotation. Traditional helical scanning (some call spiral) has the advantage of being faster than non volumetric axial scanning and also …

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beamQuality 400

Beam Quality, Beam Quantity (mA, kVp, HVL) for Radiologic Technologist

Beam Quality describes the shape of the energy spectrum (i.e. the energy distribution of the x-rays) and beam quantity describes the total intensity of the spectrum (i.e. the area under the x-ray spectrum curve). In this post we describe the factors affecting beam quality including: kVp, target material, and pre-patient collimation. We also discuss the …

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gonadShielding 400

5 reasons why Gonad Shielding will soon be extinct, and motivations for why it was introduced.

The motivation for gonad shielding is to reduce the hereditary specific risks of radiation, and it is still common practice at many institutions. The reasons that shielding will soon be phased out include: hereditary risk in humans has not been demonstrated even at high doses, the radiation doses have reduced greatly from the 1950s (orders …

5 reasons why Gonad Shielding will soon be extinct, and motivations for why it was introduced. Read More »

X rayInteractions 400

X-Ray Interactions, Illustrated Summary (Photoelectric, Compton, Coherent) for Radiologic Technologists and Radiographers

The x-ray interactions are Photoelectric, Compton and Coherent. Photoelectric is mainly responsible for image contrast, Compton contributes to artifacts in the images, and Coherent scattering has little influence in most diagnostic (x-ray/CT) procedures. Overview of the Physics Behind X-Ray Interactions When x-rays interact with the human body during an x-ray exposure, they form an image …

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scatter 400

X-ray scatter (collimation, kVp, air gap, thickness, anti-scatter grids) factors every technologist should know.

X-ray scatter due to Compton Scatter generates background haze in x-ray images and there is a desire to reduce the scatter impact on image quality. X-ray scatter depends on several physical factors including: body habitus (increases with increased habitus), kVp, collimation (increases with increased kVp), air gap (decreases with increased air gap), and anti-scatter grids …

X-ray scatter (collimation, kVp, air gap, thickness, anti-scatter grids) factors every technologist should know. Read More »

x rayGeneration 400

X-ray Generation, pictorial Guide [Bremsstrahlung, Characteristic]

X-ray tubes used in diagnostic X-ray exams all use the same physical principles including: thermionic emission (boiling off electrons), accelerating electrons by a kiloVoltage potential (kVp), and two physical interactions contribute to x-ray generation: bremstraalung (breaking radiation), and characteristic radiation (peaks in energy spectrum). The output x-ray distribution as a function of energy is termed …

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ctGenerations 400

Animated CT Generations [1st, 2nd, 3rd, 4th, 5th Gen CT] for Radiologic Technologists

CT scanning prototypes were developed in the late 1960s and this post describes the stages of technological development for CT scanners (Generations 1-5). After demonstrating the differences between these generations of scanner we describe how the 3rd generation became the dominant architecture and discuss the common projection geometries of parallel beam, fan beam and cone …

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