by Dave Skipper
This is a follow-up to Intestinal Strangulation, where I shared my thoughts in hospital following emergency abdominal surgery for bowel obstruction a few weeks back. Short update: the surgery was a complete success, having averted a potentially very serious situation, and I am well on the way to full healing.
What had actually happened? Somehow or other (the doctors can’t tell how or why), part of my small intestine had got trapped inside some fatty tissue that lines the colon. This cut off the blood supply to that area, and the intestine became engorged either side of the strangulation. Hence the severe pain. If this kind of obstruction is not fixed, then the affected area becomes necrotic (the cells and tissue die) and rotten. If this is not removed then the build-up continues, the intestine ruptures, and the body is sent into shock. Certain death awaits. In my situation, they operated before any necrosis set in (though it was probably not long before that process would have started), so they only needed to cut and remove the offending tissue that was around the intestine, and check that the intestine’s colour went back to normal. This was the simplest version and outcome given the scenario, phew! The surgery lasted nearly two hours, and was performed via 3 small holes in my abdomen, with an internal camera to guide the way. Amazing!!
At my post-op checkup this week I was able to look at the CT scan (3D x-ray) that they took when I was rushed into hospital. The two large grey stubby tubes are the expanded sections of my small intestine, and the strangulated part connecting them is very easy to see:
I was marvelling at the technology and knowledge that is behind this kind of x-ray imaging, and wondering how I could connect it to noise in order to justify making a blog post about it, ha! The answer is Quantum Noise…
There are factors that tend to produce variation in the brightness of a displayed image even when no image detail is present. This variation is usually random and has no particular pattern. In many cases, it reduces image quality and is especially significant when the objects being imaged are small and have relatively low contrast. This random variation in image brightness is designated noise.
All medical images contain some visual noise. The presence of noise gives an image a mottled, grainy, textured, or snowy appearance. No imaging method is free of noise, but noise is much more prevalent in certain types of imaging procedures than in others.
In all imaging procedures using x-ray or gamma photons, most of the image noise is produced by the random manner in which the photons are distributed within the image. This is generally designated quantum noise. Each individual photon is a quantum (specific quantity) of energy. It is the quantum structure of an x-ray beam that creates quantum noise. X-ray photons impinge on a surface, such as an image receptor, in a random pattern. No force can cause them to be evenly distributed over the surface. One area of the receptor surface might receive more photons than another area, even when both are exposed to the same average x-ray intensity.
Quantum noise can be reduced by increasing the concentration of photons (i.e., exposure) used to form an image.
The relationship between image noise and required exposure is one of the issues that must be considered by persons setting up specific x-ray procedures. In most situations, patient exposure can be reduced, but at the expense of increased quantum noise and, possibly, reduced visibility. It is also possible, in most situations, to decrease image noise, but a higher exposure would be required. Most x-ray procedures are conducted at a point of reasonable compromise between these two very important factors.
It should be evident that such phenomena as quantum noise are entirely natural and to be expected. The statistically random variations that cause many types of visual and audio noise are not inherently problematic, and indeed when aggregated en masse noise helps provide the repeatable predictability of many systemic characteristics and behaviours. Noise performs necessary functions, and brings particular aesthetics along for the ride too (I quite like the grainy effect). Visual noise becomes problematic depending on the nature, extent, context, and need for clarity and precision of knowledge within specific applications. In the case of my CT scan, there was obviously no need for the effects of quantum noise (and other forms of visual noise that come from the imaging equipment, computer screen composition, etc) to be any more diluted in order to ascertain where and what the basic problem was. But they couldn’t tell until they got inside me that there was no necrosis, and that it was the colon’s surrounding fat tissue that was the specific culprit. As medical technology advances, and ways to mitigate or bypass the detrimental effects of high-dosage radiation are discovered, I am sure that current CT scan imaging will look very primitive in decades or centuries to come.
We don’t normally get the chance to look inside our bodies, but they are truly amazingly designed!
For you created my inmost being;
you knit me together in my mother’s womb.
I praise you because I am fearfully and wonderfully made;
your works are wonderful,
I know that full well.
My frame was not hidden from you
when I was made in the secret place,
when I was woven together in the depths of the earth.
Your eyes saw my unformed body;
all the days ordained for me were written in your book
before one of them came to be.
How precious to me are your thoughts, God!
How vast is the sum of them!
Were I to count them,
they would outnumber the grains of sand –
when I awake, I am still with you.
From the Bible – Psalm 139:13-18