Current Issues in Biomedical Imaging

When it comes to modern medical imaging, I believe that many of my friends are not unfamiliar with it. Chest X-ray, ultrasound, CT and even MRI have become more popular in major hospitals in China. So, to ask the simplest question, why do we need medical imaging? And, what is the significance of the various medical imaging results we get from hospitals?

For a patient, a doctor needs to know exactly what's going on in the patient's body (superficial trauma doesn't count, of course). In Chinese medicine, there is observation and examination, and Western medicine has developed its own anatomy and examination of various physiological parameters. However, it is still difficult to confirm the diagnosis of many diseases by simple percutaneous examination and patient's self-report, therefore, major Chinese hospitals have introduced modern diagnostic techniques one after another. Although Western medicine is specialized in surgery, supplemented by various tests such as biopsy, blood test, urine test, etc., surgery is more harmful to the human body, and it is difficult to determine the specific location of the lesion by various tests. Therefore, we need to be able to understand the physiological structure of the patient's body and the location of the lesion with little or no harm to the patient.

But we can't see the structures and lesions with the naked eye because visible light has too little penetration and decays very quickly in the body's tissues. A thin layer of eyelids will allow you to easily face the sun without being blinded by the light, and it is almost impossible to use electromagnetic waves in the visible range to probe the internal tissue structure of the human body at a depth of tens of millimeters or even tens of centimeters. But scientists and engineers have invented all sorts of wonders to solve this problem:

1. Endoscopy

The principle of endoscopy is the simplest: Since you can't see it from the outside, let's look at it from the inside.

Passing a catheter that transmits a light path through various body orifices, we are able to observe tissue structures and lesions inside the body directly from the outside. It sounds simple enough, yet endoscopic technology has been evolving for nearly two full centuries, and to this day it's still not a test that's all that comfortable for patients and healthcare professionals. Even with gastroscopy, the patient's instinctive oral reflex to try to vomit up a foreign object that has entered the esophagus often makes the procedure very painful. Not to mention colonoscopies and colposcopies, which are psychologically disturbing for many patients. Cutting-edge research is now experimenting with capsule endoscopy, which has good potential to greatly reduce patient suffering. However, it is not currently practical and has major limitations in terms of imaging clarity, site-specific imaging and resolution compared to conventional endoscopy. For example, for the liver, kidneys and other substantial organs (that is, people are solid not hollow), endoscopy is completely helpless.

The picture above is a simple schematic diagram of enteroscopy (source: enteroscopy_benxu_new_wireless_blog). I don't know what you think of it, but it hurts me to look at it.

2. X-ray imaging

Since visible light is not very penetrating, let's go for something stronger ......

Visible light is an electromagnetic wave with a wavelength between 400 and 760nm. According to the formula, photon energy, where c is the speed of light, h is Planck's constant, is the wavelength, is the frequency. The short answer is that the shorter the wavelength, the higher the energy of the photon, and roughly speaking the more penetrating it is. Since wavelengths of a few hundred nanometers are too long, let's go a few nanometers: x-rays. Below is a simple diagram of the electromagnetic spectrum (source: Baidu Encyclopedia).

X-rays were originally discovered by Wilhelm Roentgen in 1895. Rumor has it that Roentgen accidentally discovered film sensitized in a dark room. After ruling out the possibility of cathode rays, he thought it was an "unknown" ray and named it X-rays. And driven by strong curiosity, he was dead with X-rays to look at his own hand, and found that he could magically see the bones ...... Therefore, X-ray imaging has been widely used to observe the bones to the present day. Legend has it that this is R?ntgen's first X-ray photo of his wife:

Why I say the word "death", I will later X-ray and CT chapter describes the hazards of X-rays in detail.

As for CT, its full name is computed tomography, that is, computed tomography. Currently, X-rays are predominantly used in hospitals, so X-CT will be used here as an example to introduce CT technology.