1、Introduction
Radiology is the medical specialty concerned with the study and application of x-rays and other technologies (such as ultrasound and magnetic resonance) to produce and interpret images of the human body for the diagnosis of disease. X-rays are invisible waves of energy that are produced by an energy source (such as an x-ray machine or cathode ray tube) and are useful in the diagnosis and treatment of disease. Nuclear medicine is the medical specialty that uses radioactive substances in the diagnosis and treatment of disease. These radioactive substances (radionuclides) are materials that emit high-speed particles and energy-containing rays from the interior of their matter. The emitted particles and rays are called radioactivity and can be of three types: alpha particles, beta particles, and gamma rays. Gamma rays are used effectively as a diagnostic label to trace the path and uptake of chemical substances in the body.
放射學是研究和應用x射線和其他技術(如超聲波和磁共振)來做出和解釋人體圖像，來診斷疾病的醫學專業。x射線是由能量源(如x光機或陰極射線管)產生的不可見的能量波，對疾病的診斷和治療有很大作用。核醫學是利用放射性物質進行疾病診斷和治療的醫學專業。這些放射性物質(放射性核素)是從物質內部發射高速粒子和含能射線。發射出粒子和射線的能力稱為放射性，放射性物質有三種類型：α粒子，β粒子和γ射線。γ射線被有效地用作一種診斷工具，以追蹤化學物質在體內的路徑和吸收。
2）Characteristics of X-RaysSeveral characteristics of x-rays are useful to physicians in the diagnosis and treatment of disease.
Some of these characteristics are the following:
x射線的一些特徵對醫生診斷和治療疾病是有用的。
其中一些特徵如下：
①Ability to cause exposure of a photographic plate. If a photographic plate is placed in front of a beam of x-rays, the x-rays, traveling unimpeded through the air, will expose the silver coating of the plate and cause it to blacken.
使感光平面曝光的能力。如果把感光平面放在一束x射線前，x射線在空氣中無阻地傳播，就會使感光板的鍍銀層暴露出來，使其變黑。
②Ability to penetrate different substances to varying degrees. X-rays pass through the different types of substances in the human body (air in the lungs, water in blood vessels and lymph, fat around muscles, and metal such as calcium in bones) with varying ease. Air is the least dense substance and allows the greatest transmission. Fat is denser, water is next, followed by hard materials, such as calcium in bone, which is the densest and transmits least. If the x-rays are absorbed (stopped) by the denser body substance (e.g., calcium in bones), they do not reach the photographic plate held behind the patient, and white areas are left in the x-ray detector (plate).
能在不同程度上穿透不同物質。x光穿透人體不同類型的物質(肺部的空氣，血管和淋巴液中的水，肌肉周圍的脂肪，骨骼中的鈣等金屬)的能力各不相同。空氣是密度最小的物質，傳播力最大。脂肪密度較大，其次是水，其次是硬物質，如骨中的鈣，它是密度最大，傳遞最少的。如果x光被較密集的身體物質(如骨骼中的鈣)吸收(停止穿透)，它們就不能到達病人身後的感光板，在x光檢測器(感光板)上呈現空白區域。
③Invisibility. X-rays cannot be detected by sight, hearing, or touch. Workers exposed to x-rays must wear a film badge to detect and record the amount of radiation to which they have been exposed.
不可見。視覺、聽覺和觸覺都無法感覺到x射線。暴露在x光下的工作人員必須佩戴一個膠片標記，以檢測和記錄他們所受到的輻射量。
④Travel in straight lines. This property allows the formation of precise shadow images on the x-ray plate and also permits x-ray beams to be directed accurately at a tissue site during radiotherapy.
走直線。這種特性允許x線形成精確的圖像，也允許其在放射治療期間精確地定向併到達組織部位。
⑤Scattering of x-rays. Scattering occurs when x-rays come into contact with any material. Greater scatter occurs with dense objects and less scatter with those substances that are radiolucent. In digital imaging, an image receptor replaces film.
x射線的散射作用。當x射線與任何物質接觸時就會發生散射。密度大的物體會產生較大的散射，而那些有輻射的物質會產生較小的散射。在數字成像技術中，圖像接收器代替膠片。
⑥Ionization. X-rays have the ability to ionize substances through which they pass. Ionization is a chemical process in which the energy of an x-ray beam causes rearrangement and disruption within a substance, so that previously neutral particles are changed to charged particles called ions. This strongly ionizing ability of x-rays is a double-edged sword. In x-ray or radiation therapy, the ionizing effect of high energy x-ray beams can help kill cancerous cells and stop tumor growth; however, ionizing x-rays in even small doses can affect normal body cells, leading to tissue damage and malignant changes. Thus, persons exposed to high doses of x-rays are at risk for the development of leukemia, thyroid tumors, breast cancer, or other malignancies.
電離。x射線有使其通過的物質發生電離的能力。電離是一種化學過程，在這個過程中，x射線束的能量會導致物質內部的重排和破壞，使之前的中性粒子變成帶電粒子，即離子。x射線的強電離能力是一把雙刃劍。在x射線或放射治療中，高能x射線束的電離效應可以幫助殺死癌細胞和阻止腫瘤生長；然而，即使是小劑量的電離x射線也會影響正常的身體細胞，導致組織損傷和惡性變化。因此，暴露於高劑量x射線下的人有發展為白血病、甲狀腺腫瘤、乳腺癌或其他惡性腫瘤的風險。
①X-Ray Studies
X-ray imaging is used in a variety of ways to detect pathologic conditions. Digital radiography is a form of x-ray imaging in which digital x-ray sensors are used instead of traditional photographic film. Thus images can be enhanced and transferred easily, and less radiation can be used than in conventional radiography. The chest x-ray is the most commonly performed diagnostic x-ray examination. Mammography uses low-dose x-rays to visualize breast tissue.
①x射線
x射線成像用於多種方式來檢測疾病。數字射線照相是x射線成像的一種形式，用數字x射線傳感器代替傳統的照相膠片。因此，圖像可以容易地被加強或轉換，並可以比傳統的射線照相使用更少的輻射。胸部x光檢查是最常見的診斷性x光檢查。乳房x線照相術使用低劑量x射線來可視化乳房組織。
②Computed Tomography (CT)
The CT scan, sometimes called 「CAT scan」 (because the technique originally was known as 「computerized axial tomography」), is made by beaming x-rays at multiple angles through a section of the patient's body. The absorption of all of these x-rays, after they pass through the body, is recorded and used by a computer to create multiple cross-sectional images. The ability of a CT scanner to detect abnormalities is increased with the use of iodine-containing contrast agents, which outline blood vessels and confer additional density to soft tissues.
②計算機斷層掃描(CT)
CT掃描，有時也被稱為「CAT掃描」(因為這項技術最初被稱為「計算機軸向斷層掃描」)，是將x射線從多個角度射向病人身體的一個部位。所有這些x射線經過人體吸收後的情況會被記錄下來，並由計算機生成多個橫截面圖像。含碘造影劑的使用，增強了CT掃描儀檢測異常的能力，這種造影劑能勾勒出血管輪廓，增加軟組織的密度。
③Contrast Studies
A contrast material used in diagnostic radiologic studies: Barium Sulfate. Barium sulfate is a radiopaque substance that is mixed in water and used for examination of the upper and lower GI (gastrointestinal) tract. An upper GI series (UGI) involves oral ingestion of barium sulfate so that the esophagus, stomach, and duodenum can be visualized. A barium enema (BE) study is a lower GI series that opacifies the lumen (passageway) of the large intestine using an enema containing barium sulfate. This test has largely been replaced by endoscopy, which allows visualization of the inside of the bowel. A double-contrast study uses both a radiopaque and a radiolucent contrast medium.
用於診斷放射學研究的造影劑——硫酸鋇，是一種不溶於水的不透明物質，用於檢查上、下消化道。上消化道系列(UGI)包括口服硫酸鋇，可以看到食道、胃和十二指腸。鋇劑灌腸(BE)是利用含有硫酸鋇的灌腸液觀察不透明的下消化道——大腸腔。這種檢查在很大程度上已經被內窺鏡所取代，內窺鏡可以讓你看到腸道內部。雙重對比研究使用了不透明和透明的對比介質。