X-Ray • How Radiology Works

What is Computed Radiography? (Illustrated guide for Rad Techs)

Computed Radiography (CR) is a method to generate digital images in x-ray radiography that uses photo-stimulated luminescence to store the x-ray exposure into a latent image, that is then digitized. Computed Radiography is rapidly replacing film screen radiography, and at the same time a newer technology termed Digital Radiography (DR) is beginning to displace CR …

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Digital Radiography (Direct vs Indirect Flat panels)

X-Ray, Physics

Digital radiography detectors are used to directly acquire x-ray images in place of film or computed radiography (CR) systems and are separated into direct and indirect detectors. Direct detectors convert from the x-rays electrons (that are measured), whereas indirect detector convert from x-rays to visible light first and then to electrons (that are measured). Digital …

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X-ray physics intro for starting x-ray school, a step by step guide for new radiologic technologists (radiographers).

Physics, X-Ray

If you are a student in training or totally new to x-ray physics are you feeling: overwhelmed or confused with the all the terminology and physics concepts pressured or embarrassed that you don’t know the answers to questions from senior technologists during your clinicals unsure of radiation effects and nervous about mass media coverage you …

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X-ray Contrast to Noise (CNR) Illustrated examples of image noise (SNR, Quantum Mottle) for Radiologic Technologists

Physics, X-Ray

The Contrast to Noise Ratio (CNR) in a medical image is a measure of the contrast between the tissue of interest and the background (i.e. the neighboring tissue). The Signal to Noise Ratio (SNR) is a measure of the image signal in a given region to the background. The ability to visualize objects in a …

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X- ray Resolution (PSF, MTF, NPS, DQE) for radiologic technologists

Physics, CT, X-Ray

The spatial resolution of an x-ray or CT system is a measure of how the ability of a system to differentiate small structures. If you imagine imaging a very small point like object an image of that object is called the Point Spread Function (PSF). When this function is radially averaged the Line Spread Function …

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X-ray attenuation of tissues [thickness, atomic number] for Radiologic Technologists

Physics, X-Ray

In x-ray imaging (radiography and CT) the contrast between the tissues in the image is generated by the difference between the x-ray attenuation (influenced by density and atomic number). In this post we demonstrate the material dependence for x-ray attenuation. For all radiographers, radiologic technologists and students understanding the basic principles of x-ray interactions, which …

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Magnification and Blurring Effects for Radiographers and Radiologic Technologists (with Focal Spot Blur Formula)

Physics, X-Ray

Magnification occurs in x-ray imaging because the x-rays are divergent or spread out from the x-ray source. Therefore, the object will appear larger on the detector than the true object size. Magnification in radiography is defined as (Image Size/Object Size) and is equal to the (SID/SOD) which is the source to image distance divided by …

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

Physics, CT, X-Ray

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

Physics, CT, Dose, X-Ray

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 …

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

Physics, CT, X-Ray

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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