Recent studies have concluded that CT radiation is more likely to cause cancer than previously thought and that people should pay attention to the dangers of excessive CT use; and asserted that: CT now accounts for 67% of the received dose released and patients have the highest CT dose in diagnostic radiology; it is also estimated that an adult abdominal examination with an effective dose of 10 mSv increases the risk of cancer by 1/2000. thus, the small risk of cancer in individuals becomes a larger public health issue, so what exactly is the relevance of multi-row CT radiation?
CT scanners currently in use
In China, the new CT scanner DD multi-row detector CT has been equipped to the county level, which is equipped with 2 or more detectors arranged in parallel, using the third generation technology of synchronous rotation of the bulb and detector array. It is also known as a multilevel CT scanner because its X-ray bulb rotates for one week to obtain images of multiple levels. Dual-detector or multi-detector systems were available in the early 1990s, and multi-detector CT soon became accepted by radiologists, exceeding 1,000 units by the end of 2000, with an almost exponential increase in the number of such CT scanners in use worldwide.
Advantages of multi-detector CT
The advantages of multi-row detector CT include better density and spatial resolution, faster scanning speed, and larger scan volume. Scanning speed can reach 0.37 seconds, and the acquired data achieves isotropy in the X, Y, and Z directions, allowing for higher contrast utilization. Coupled with its use of automatic vascular scanning tracking technology, it enables consistent enhancement of the examined site, avoiding the enhancement effect of the image due to the patient’s fast or slow blood circulation or the operator’s misjudgment of the delayed scanning time. Thus, multi-row detector CT extends the clinical application of CT and advances CT from pure morphological diagnosis to functional diagnosis, such as: perfusion imaging of brain and lung, dynamic cardiac function analysis, and real-time 4D imaging. The performance of 16-layer CT is said to be more than 25 times that of conventional spiral CT scanners. What’s more, today’s 64-layer CT machines are becoming widely available, and 256-layer CT is about to be used in clinical applications.
Radiation Dose
Multi-row detector CT can adjust the X-ray radiation dose according to the patient’s body thickness and density during the whole scanning process, changing the uniform X-ray dose regardless of the patient’s physical condition in the past, and individualizing the X-ray dose, making it possible for low-dose and ultra-low-dose CT scanning, especially for high-contrast structures, such as lungs or bones, only 1mSv effective dose can be used for pulmonary vascular CT. examination effect is done well. Ultra-low dose applications can be reduced to less than 0.4mSv, a dose equivalent to the sum of conventional posterior anterior and lateral chest films using a 100-speed screen-slice system.
”Ionizing radiation is a necessary energy”
It is well documented that radiation induced cancer doses are not linear and only threshold dose rates exceeding 1 Gy/year induce cancer. It has been shown through today’s workers engaged in radiation that radiation at appropriate dose rates significantly reduces non-cancer mortality. Therefore, it has been suggested that ionizing radiation may be “an essential particle energy”, similar to the multiple particle elements we need for a good body. It has been shown that the natural radiation environment in the Rocky Mountains has an annual average level 3.2 times higher than that of the Mexican coast, but the average cancer mortality rate in the Mexican coast is 1.26 times higher than that of the Rocky Mountains. It may be that appropriate radiation doses stimulate the immune system to the point of generating the unpalatable hypothesis that we need increased radiation to improve our health.
CT exams in the spotlight
How can such a low dose CT exam be the focus of attention today? When CT first came into clinical use, it was considered a relatively high dose technology, but the use of CT exams has outlived its clinical value. At that time, there was no technology in the brain that could reach the level of CT, that is, when CT in the body started to be used, it was mainly used for patients with malignant lesions. Therefore, its radiation dose was less of a concern. But now it is different, CT technology is more widely used, not only for younger patients, but also expanded to patients with benign lesions. Therefore, radiation protection is considered to be a top priority.
Reasons for increased dose
There is a causal relationship between image quality and radiation dose. Sometimes, in order to increase image resolution or reduce image noise, we need to increase the radiation dose of the scan, which may be beneficial for diagnosis, but at the same time the patient is additionally exposed to more x-ray radiation. Although the care of the imaging patient is the primary responsibility of the medical imager, without good image quality there is the possibility of missed diagnoses, and for this reason the image quality must be improved, but this again comes at the cost of access to radiation.
The trend of a significant increase in public dose is attributed to the rise in the use of CT, mainly because of the ease of use, the fact that early CT scans had strict indications for examination and the fact that carrying out this examination meant that it was time consuming. Today, the use of new technologies has led to an increasing number of indications for the diagnostic range of CT, and clinicians are increasingly coming to rely on imaging, coupled with an increase in medical lawsuits, patient superstition about CT, etc., the use of CT utilization is rising significantly.
Hazards of radiation
CT examination is a kind of X-ray examination, and X-rays are ionizing radiation, which will produce biological effects and cause harm to the human body in the process of action. The radiation dose of one scan, in addition to the dose in the scan level, there is also a considerable dose of scattered rays in the area outside the scan range.DNA double helix structure breakage is the key damage leading to cellular effects, radiation induced mutation genes or from the double helix structure breakage aberration increase can eventually lead to cancer.
Children are more sensitive than adults
When adult radiation doses are applied to newborns or young children, the dose effect rises by more than 50%. This result is due to the fact that the central dose for large objects (adults) is half of the surface dose, while for small objects (children) the central dose is almost the full surface dose. In addition, children are more than 10 times more sensitive to the effects of radiation than middle-aged adults, and girls are more sensitive to radiation than boys. The odds of cancer death from radiation exposure in children are expected to be 2-4 times higher per dose unit than in adults, and both the rapid cell proliferation of children and their own longer average life span contribute to their increased risk of after-effects.
Factors affecting radiation damage
The biological effects caused by the action of X-rays on the body are influenced by the nature of the radiation (type and energy), the X-ray dose, the dose rate, the mode of exposure, and the site and extent of exposure; also, there is a degree of variation with age, gender, health status, mental status, and nutrition; and there are also differences in tissue receptivity to X-ray exposure.
Highly reactive tissues: hematopoietic tissue, lymphatic tissue, gonads, intestinal epithelium, fetus. Moderate-high receptor tissues: oral mucosa, salivary glands, hair, sweat glands, skin, capillaries, eye lens. Mesoreceptive tissues: brain, lung, pleura, kidney, renal gland, liver, blood vessels. Low to medium receptor tissues: thyroid, spleen, joints, bone, cartilage. Low receptor tissues: adipose tissue, nerve tissue, connective tissue.
The purpose and principles of radiation protection
The purpose of radiation protection is to safeguard the health and safety of the examinees and radiation work and their offspring, to prevent the occurrence of harmful non-random effects, and the incidence of random effects should be limited to acceptable levels. To this end, a dose limitation system must be established: it includes three basic principles: justification of radiation practices, optimization of protection levels, and personal dose limits.
Justification of radiation practice means that radiological examinations in medical imaging must have indications to avoid radiation exposures that bring negative diagnostic and therapeutic effects to patients. Optimization of radiation protection means that the radiation exposure dose implemented should be kept at the lowest possible reasonable level while ensuring the diagnostic and therapeutic benefit to the patient.
In addition, extra-irradiation protection must be established, including: shortening the duration of exposure, increasing the distance to the radiation source, and shielding protection. In a word: reasonable reduction of individual exposure dose with universal examination frequency.
Protection of the examinees
For the examinees, the first thing is to improve the national knowledge level of radiation protection. Because X-rays have certain harm to the human body, avoid some unnecessary examinations as much as possible; cooperate with the doctor in the scan as much as possible, and make adequate preparation before the examination to reduce unnecessary repeated scans.
For the operator, it is necessary to correctly select the indications for X-ray examination; to improve the sensitivity of the image conversion medium; to avoid operational errors and reduce the rate of waste films and retakes; to obtain the cooperation of the patient as much as possible during the scan and reduce unnecessary repeat scans; to let the accompanying person leave as much as possible during the scan, and if necessary, to let the accompanying person wear lead protective clothing and stay as far away from the bulb as possible; and to scan as small as possible without affecting the diagnosis. In the case of scanning, the scanning field should be reduced as much as possible to lower the scanning dose; for patients, the shielding protection should be done outside the scanning area; the X-ray protection and leakage of the scanning machine room should be tested regularly; and the rules of protective safety operation should be strictly enforced.
Personal dose equivalent limits for the public, i.e., the annual dose equivalent of radiation exposure to the public should be lower than the following limits: whole body: 5 mSv (0.5 rem); individual tissues or organs: 50 mSv (5 rem). Medical imaging scientists, manufacturers, and national oversight agencies must work together to minimize the radiation dose from CT, and must be fully aware that children have a high sensitivity to radiation to ensure that the lowest dose diagnostic images are obtained, making the rational use of low dose (ALARA) a reality