Question

1. List the viewing systems for fluoroscopy. What is SNR? What would be an acceptable SNR for a fluoro viewing system? (2 points)

Answer 1

what is SNR?

ANSWER:-

signal-to-noise ratio

the ratio of the strength of an electrical or other signal carrying information to that of unwanted interference.

Signal-to-noise ratio (abbreviated SNR or S/N) is a measure used in science and engineering that compares the level of a desired signal to the level of background noise. SNR is defined as the ratio of signal power to the noise power, often expressed in decibels. A ratio higher than 1:1 (greater than 0 dB) indicates more signal than noise.

que:- list of viewing systems for fluoroscopy

and:-

Fluoroscopy  is an imaging technique that uses x-ray to obtain real-time moving images of the interior of an object. In its primary application of medical imaging, a fluoroscope allows a physician to see the internal structure and function of a patient, so that the pumping action of the heart or the motion of swallowing, for example, can be watched. This is useful for both diagnosis and therapyand occurs in general radiology, interventional radiology, and image-guided surgery. In its simplest form, a fluoroscope consists of an X-ray source and a fluorescent screen, between which a patient is placed. However, since the 1950s most fluoroscopes have included X-ray image intensifiers and cameras as well, to improve the image's visibility and make it available on a remote display screen.

Figure 1. Schematic Diagram of a fluoroscopic system using an X-ray image intensifier (XRII) and video camera

SNR. The signal-to-noise ratio (SNR) is a quantitative way of expressing how noise compares to the signal. In other words, if our signal is really strong (black and white), then even a large amount of noise isn't a problem. On the other hand, if our signal is weak, such as a subtle liver lesion, then even a small amount of noise can create a problem. Sometimes, the term contrast-to-noise ratio (CNR) is used with a similar meaning. If the signal is expressed as a contrast in the image, then we can express the signal S as a change in the background intensity I determined by the contrast C. In other words

S = C * I

Note that the background intensity is just the number of photons that pass through - which we will call N - so we can just replace I with N. And remember that noise = σ = √N. Therefore,

S = C * N so SNR = S/σ = C * N / √N = C * √N

In other words, in x-ray imaging, SNR increases with dose* - specifically, with the square root of the number of photons. (*Here I mean if you increase the number of photons specifically; the relationship between SNR and kV is more complex since kV changes the contrast as well.)

Signal-to-noise ratio (SNR) is a generic term which, in radiology, is a measure of true signal (i.e. reflecting actual anatomy) to noise (e.g. random quantum mottle). A lower signal-to-noise ratio generally results in a grainy appearance to images.

Each modality has its own source(s) of noise and therefore techniques for signal-to-noise ratio maximization are modality-specific.