Overview Of Various Medical Imaging Examination Techniques

X-ray,CT,MRI,DSA

 

 Characteristics

 

After passing through the human body, X-rays are converted into images of density differences through analog or digital means. These different grayscale images reflect the anatomical and pathological state of human tissue structure. For tissues or organs lacking natural contrast, a certain amount of substance with a density higher or lower than that of the human body can be artificially introduced, which is called contrast imaging examination.

 

X-ray examination - easy to operate, cost-effective, and low cost.

 

 

Main Purpose

 

（1） Diagnosis of bone and joint diseases: fractures, inflammation, tuberculosis, tumors.

 

（2） Diagnosis of chest diseases; Diagnosis of gastrointestinal diseases, including pneumonia, lung abscess, tuberculosis, lung, mediastinum, breast tumors, and the size and shape of the heart.

 

 (3)   plain film: gastrointestinal perforation, intestinal obstruction, and other diseases; Gastrointestinal imaging examination: can display changes such as polyps, tumors, inflammation, tuberculosis, etc., and understand their functional changes.

 

（4） Diagnosis of urinary system diseases, plain film: tuberculosis, calcification, stones; Contrast examination: It can display the morphology of the renal pelvis, renal pelvis, ureter, and bladder, and can diagnose lesions such as tumors, inflammation, stones, and congenital malformations.

 

Main Content

 

X-ray examination techniques can be divided into ordinary X-ray examination and contrast examination.

 

Ordinary X-Ray Examination

 

1.Fluoroscopy is a method of examination that utilizes the penetrability and fluorescence of X-rays to place the subject between a fluorescent screen (or image intensifier) and an X-ray tube. After the X-ray passes through the human body, a visible image is formed on the fluorescent screen (or image intensifier) and read visually. This method can observe certain organs of the human body from multiple angles, but it is now rarely used. Currently, it is mainly used for gastrointestinal imaging examination and perspective observation in interventional therapy.

 

2. Traditional plain film radiography refers to the examination method in which the subject is placed between an X-ray tube and a screen film combination system. After the X-ray penetrates the human body, a latent image is formed on the film, and then a clear film image is obtained through a development and fixation process. The obtained film is called a radiograph or plain film, and its image is called an analog image.

 

Main Advantages:

High spatial resolution and clear display of image details

For thicker areas and lesions with small differences in thickness and density, it is easier to display than fluorescence screen fluoroscopy.

Can be used as a permanent record, stored for a long time, for easy review, comparison, and consultation

Accepting less X-ray dose is beneficial for protection

 

3. Soft X-ray photography refers to X-ray photography performed using tube voltages below 40kV. Due to the low energy and weak penetration of X-rays, they are called "soft X-rays". The commonly used equipment for generating soft X-rays is the molybdenum target X-ray machine, which produces strong monochromatic identification X-rays at a tube voltage of 20-40kV and is mainly used for mammography.

 

4. Digital X-ray examination: Digital X-ray examination refers to the digital image X-ray examination technology obtained by using digital X-ray equipment for secondary examination. In a broad sense, CT also belongs to this technology, including:

● CR (Indirect Digital Photography): An inspection technique that uses an imaging plate (IP) as a carrier to record the information formed after X-ray exposure, and then reads out the information with a laser and processes the image to form a digital image. Disadvantages: Insufficient spatial resolution, complicated operation process, and relatively high radiation dose.

● DR (Direct Digital Photography): The inspection technology that detects the information of X-rays passing through the human body through a detector and converts them into digital images through photoelectric conversion or direct imaging. Its advantages include convenient operation, simple process, high image clarity, less noise, high quantum detection efficiency, relatively reduced radiation dose, and improved image post-processing function to display image details.

 

Contrast examination is a technique that introduces contrast media into or around human organs to create density differences and create image contrast. Purpose of examination: It is to form images of organs and tissues in the human body that lack natural contrast after introducing contrast agents, in order to display the morphology and function of the organs and tissues in the human body. Contrast agent: Negative contrast media, positive contrast media.

 

 

Limitations

 

Limitations of X-ray examination techniques:

 

1. Two dimensional imaging is prone to missed diagnosis.

 

2. Insufficient density resolution.

 

3. During contrast examination, a small number of patients may have contrast agent side effects and absolute contraindications.

 

Since its clinical application in the early 1970s, CT examination technology has undergone multiple upgrades and improvements in its structure and performance. It has evolved from the initial ordinary head CT machine to the current multi-slice spiral CT (SCT) and dual source CT (DSCT).

 

Characteristics

 

CT scans a certain thickness layer of the human body with an X-ray beam surrounding it. The X-ray part that passes through this layer is absorbed, and the X-ray intensity is attenuated. The unabsorbed X-ray after passing through the human body is received by the detector and converted into visible light, which is then converted into an electrical signal by a photoelectric converter. It is then converted into a digital signal by an analog-to-digital (A/D) converter and input into a computer for processing, and reconstructed into an image.

 

Compared With Ordinary X-Ray Examination, Ct Has The Following Advantages:

 

① Cross sectional imaging, with clear and realistic images and no front to back overlap, basically solves the problem of tissue and organ overlap in ordinary X-ray photos; Volume data can be reconstructed to obtain sagittal, coronal, or any oblique plane, as well as three-dimensional (3D) stereoscopic images. Different densities of tissues can be displayed in different pseudo colors, making the image display more vivid; It can also be observed from multiple angles, making the anatomical structures of normal tissues and organs and diseased tissues clearer and the localization of lesions more accurate;

 

② The spatial resolution is lower than that of X-ray photos, but the density resolution is much higher. It can distinguish tissue structures with small density differences that cannot be distinguished by ordinary X-rays, and can perform density measurements, which improves the detection rate of lesions and significantly improves the qualitative diagnosis of lesions compared to ordinary X-rays, expanding the application scope of X-ray examination.

 

 

Main Purpose

 

CT can be used for the examination of tissues and organs in any part of the body and has become a routine imaging method in clinical practice.

 

(1) Craniocerebral: It has significant diagnostic value for intracranial tumors, cerebral hemorrhage, cerebral infarction, traumatic brain injury, intracranial infections and parasitic diseases, congenital brain malformations, brain atrophy, hydrocephalus, and demyelinating diseases. CT is the preferred examination method for cranial diseases. CTA can obtain relatively fine and clear 3D images of blood vessels, but for the diagnosis of certain cerebral vascular malformations, CT is inferior to DSA MRI； The display of lesions in the skull base and posterior fossa is not as good as MRI.

 

(2) Head and neck: It has good localization, quantitative, and qualitative abilities for benign and malignant tumors of the eye socket and eyeball, eye muscle lesions, mastoid and inner ear lesions, congenital developmental abnormalities of the ear, inflammation and tumors of the sinus and nasal cavity, nasopharyngeal tumors, especially nasopharyngeal carcinoma, laryngeal tumors, thyroid tumors, and neck masses.

 

(3) Chest: can be used for diagnosing diseases of the trachea, lungs, mediastinum, pleura, chest wall, diaphragm, heart, pericardium, and aorta. CT has significant advantages over conventional X-rays in the early diagnosis of bronchial lung cancer, displaying the internal structure of lung cancer, observing lymph node metastasis in the hilum and mediastinum, and accurately locating lymph node tuberculosis and mediastinal tumors; It can also effectively display interstitial and parenchymal lesions in the lungs. CT has significant advantages in observing pericardial diseases, displaying true and false lumens of aortic aneurysms and aortic dissections, and can also effectively show calcification of coronary artery plaques and heart valves, calcification of large vessel walls, as well as myocardial and intracardiac lesions.

 

(4) Abdominal and pelvic cavity: It can be used for the diagnosis of liver, gallbladder, pancreas, spleen, kidney, adrenal gland, bladder, prostate, uterus and adnexa, abdominal cavity and retroperitoneal lesions. It plays an important role in determining the location, size, relationship with adjacent tissue structures, and lymph node metastasis of mass lesions. It can also effectively display inflammatory and traumatic lesions. For gastrointestinal lesions, CT can better display the invasion of tumors outside the gastrointestinal cavity, as well as the metastasis to nearby and distant areas. However, endoscopic examination should be the preferred method for displaying gastrointestinal intracavitary lesions. CT plays an important role in preoperative staging of abdominal and pelvic tumors.

 

(5) Spine and bone joints: can be used for the diagnosis of degenerative spinal diseases such as spinal stenosis, intervertebral disc disease, as well as spinal trauma and spinal tumors, but showing spinal cord lesions is not as sensitive as MRI. For bone and joint lesions, CT can display the internal structure of bone tumors and the extent of tumor invasion into soft tissues, supplementing the shortcomings of conventional X-ray examinations.

 

Main Content:

 

CT scans typically use axial or transverse plane scans, and coronal plane scans can also be performed on the craniofacial region. After the patient is positioned, scan the positioning map to determine the scanning range, and then start scanning according to the set scanning program. The commonly used CT examination techniques include plain scan, contrast scan, thin-layer scan, target scan, high-resolution scan, perfusion CT, CT volume scan, and 3D reconstruction. Different examination methods are adopted according to different examination sites and purposes.

 

Limit:

 

The clinical application of CT has increasingly obvious advantages, but there are also some shortcomings and limitations: ① spatial resolution is not as good as ordinary X-ray photos; ② CT distinguishes between normal and lesion based on the difference in density. When the density of the lesion is similar or equal to that of the surrounding normal tissue, CT is difficult to detect Due to the effects of partial volume effect and surrounding gap phenomenon, some small lesions may be missed in CT scans. When the density difference between the two tissues is large, the lesion density and edge distortion that are less than the scan layer thickness may occur CT contrast-enhanced scanning uses iodine contrast agent, which has a large dosage and fast injection speed. It can cause adverse reactions and even allergic reactions to the contrast agent. Individuals with iodine allergy should not undergo contrast-enhanced scanning X-rays have ionizing radiation effects on tissues, causing damage to the human body.

 

Characteristics of MRI examination technology:

 

MRI excites hydrogen protons in human tissues by applying specific frequency radio frequency (RF) pulses to the human body in a static magnetic field, resulting in magnetic resonance phenomenon. After stopping the transmission of RF pulses, hydrogen protons induce MR signals in the receiving coil during the relaxation process. After signal acquisition, spatial encoding, and Fourier transform, a human body tomographic image is reconstructed.

 

 

MRI has the following characteristics: 1. Multi parameter imaging, multi sequence, multi orientation, high soft tissue resolution. 2. Non ionizing radiation, safe and non-invasive for the human body. 3. Can be used for functional, histological, and biochemical research.

 

Main Purpose

 

(1) Central nervous system (2) Head and neck (3) Bone and joint system (4) Cardiovascular system, etc.

 

limit

 

(1) Cardiac pacemakers and ferromagnetic materials (excluding compatibility)

(2) critically ill patients

(3) insensitive to small calcifications and dense bone display

(4) Large noise and artifacts, long inspection time

 

DSA examination technique

 

Features:

 

(1) High density resolution

(2) Fast imaging speed and high time resolution

(3) Subtracting structures other than the contrast cardiac vessels, only retaining the contrast vascular images

(4)High sensitivity to trace iodine, low contrast agent dosage and concentration

(5) Vascular pathway map function, which can be used as a guide for intubation

(6) Can be used for dynamic functional research

(7) It has multiple post-processing functions, effectively increasing diagnostic information (8). Image digitization facilitates image processing, storage, transmission, and remote consultation.

 

Main Content:

 

Using arterial DSA method, time subtraction is the most commonly used method to determine DSA imaging parameters, post-processing, selection of contrast agents, and puncture techniques. DSA is not only used for the diagnosis of vascular diseases, but also for minimally invasive interventional treatment of vascular diseases and tumors.

 

Limit:

 

(1) The resolution of venous DSA subtraction images is low and the image quality is poor.

(2) It is a traumatic examination.

(3) The radiation dose is high.

(4) A small number of patients may experience side effects of contrast agent iodine.