Difference and relationship between density resolution and spatial resolution in medical imaging

1, different resolutions

The (1) density resolution indicates the minimum density difference that can be displayed in the image.

(2) The density resolution of CT is limited by noise and display size. The smaller the noise, the larger the display and the better the density resolution. The density resolution of CT images is much higher than that of X-rays.

2. Different expressions

The degree of density difference that can be distinguished by density resolution is expressed in%. One of the indexes of computer tomography performance and image quality, if the density resolution of computer tomography is 0.5%, it means that two substances can be distinguished when the density difference is equal to or greater than 0.5%, but when the density difference is less than 0.5%, they cannot be distinguished due to noise interference.

Second, contact

Spatial resolution is sometimes called geometric resolution or high contrast resolution in CT equipment, which refers to the ability to distinguish fine structures under high contrast, that is, the ability to display the smallest volume lesions or structures. When evaluating the quality of CT images, spatial resolution is often considered first.

Because the detector of CT image has a certain size and the sampling distance is also certain, the spatial resolution of CT image is determined by the geometric size of the focus of X-ray tube, and basically has nothing to do with X-ray dose. In the case of a certain X-ray dose, there is a certain restriction between spatial resolution and density resolution, so it is impossible to improve spatial resolution and contrast resolution at the same time.

Extended materials:

Medical imaging: X-ray, CT, MRI? Imaging technology and clinical application?

A, image archiving and transmission system (PACS) is to save and transmit images of equipment and software system, its advantages are:

1, the image information is saved for later use;

2. Doctors far away from the radiology department can consult the images for reading and diagnosis at any time, which improves the work efficiency;

3. It is convenient for image transmission and communication, and can be used for composite image diagnosis and multidisciplinary consultation;

4. It can avoid the loss and mistakes of film in the transmission process and become a modern management means of the hospital;

5. Save film cost and management cost, and reduce storage space, thus entering the film-free era. ?

Second, digital subtraction angiography (DSA)? Digital image information is processed by calculator, and time subtraction is often used to eliminate bone and soft tissue images, so that blood vessels can be clearly developed. ?

Cerebral angiography? It is a method of introducing organic iodine contrast agent into cerebral vessels to display cerebral vessels, including carotid angiography and vertebral artery angiography. DSA technology is often used to capture the images of cerebral arterial phase, venous phase and venous sinus phase respectively. ?

X-ray imaging _ electromagnetic wave, wavelength 0.0006~50nm?

Three. The principle of X-ray imaging is related to penetrability, fluorescence effect and photosensitive effect, and also to the difference of density and thickness of human tissue structure. The characteristics related to imaging are as follows:

1, penetrating the basis of X-ray imaging. The higher the voltage, the stronger the penetration; ?

2. The basic fluorescence effect of fluoroscopy. X-rays excite zinc cadmium sulfide and calcium tungstate to emit fluorescence;

3. Photosensitive effect? The basis of x-ray photography. Silver ions in silver bromide were reduced to metallic silver and deposited in thin films.

4. Ionization effect? The basis of radiotherapy. X-rays injected into human body cause biological changes, that is, biological effects. ?

Four, X-ray image characteristics:

1, grayscale image;

2. Overlapping images;

3. Enlarge the image;

4. There may be distortion. ?

5. Gray image reflects the anatomical and pathological state of human tissues and structures with optical density. Besides the thickness, the white shadow and black shadow on the image mainly reflect the tissue density (high density is white shadow, low density is black shadow).

Fluoroscopy test of intransitive verbs

1, advantages: the patient's posture can be rotated; Understand the dynamic changes of organs; In terms of operation, the cost is low; ?

2. Disadvantages: poor contrast and clarity; Lack of objective records. ?

Seven, X-ray photography

1, advantages: good contrast and clarity; ?

2. Disadvantages: there is no three-dimensional concept; Unable to observe the function. ? 5. Comparative inspection? The contrast agent is introduced into the body to produce artificial contrast. The commonly used contrast agents are:

Eight, high density contrast agent

1, barium agent: medical barium sulfate; ?

2. Iodine agents: inorganic (iodized oil, iodobenzene ester) and organic (ionic type such as meglumine diatrizoate; Non-ionic type such as iodine Pierer, You Weixian). ?

Ionic contrast agent has high permeability and great toxic and side effects; Non-ionic low permeability, low age and low toxicity.

9. Low density contrast agent? Air, oxygen, carbon dioxide?

X. contrast mode

1, indirect introduction: IVP；; ; ?

2. Direct introduction: oral administration, perfusion and puncture injection. ? Five clinical applications? Gastrointestinal tract, skeletal system and chest are the majority. ?

XI。 CT imaging _ Irradiate a certain layer of human body with X-ray beam, measure the transmitted X-ray quantity, digitize it, get the absorption coefficient per unit volume of this layer of tissue by computer, and then reconstruct the image. ?

1, CT image characteristics

(1) Advantages: the density resolution is high, and the quantitative value (CT value) indicates the density grade.

(2) The spatial resolution is not as good as that of X-ray images.

(3) Multiple continuous slice images are needed. ?

2. CT value of human tissue

(1) water: 0? Hu;

(2) Air: _ 1000? Hu; ?

(3) Fat: _90~_70? Hu; ?

(4) soft tissue; 20~50? Hu;

(5) Bone:+1000? Hu.

3. Clinical application

(1) Central nervous system diseases: intracranial tumors, abscesses and granulomas, parasitic diseases, traumatic hematoma and brain injury, ischemic cerebral infarction and cerebral hemorrhage.

(2) Space occupying lesions in the frame, sinus cancer, nasopharyngeal carcinoma, etc.

(3) Lung cancer and mediastinal tumor.

(4) Liver, gallbladder, pancreas, spleen, abdominal cavity and retroperitoneal space, adrenal gland and urogenital system.

(5) Gastrointestinal diseases invade or transfer to the outside of the cavity. ?

Twelve, MRI imaging _ magnetic resonance signal has parameters such as T- 1, T2, proton density, etc., forming an MRI image. ?

T- 1-？ When the RF pulse is terminated, the longitudinal magnetization gradually returns to its initial state. This process is longitudinal relaxation, and the time required for recovery is longitudinal relaxation time, abbreviated as T- 1. The image with T 1 parameter is T 1 weighted image (T- 1-WI). ?

T2？ The transverse magnetization also disappears quickly. This process is transverse relaxation, and the required time is transverse relaxation time, T-2 for short. The image composed of T2 parameters is a T2-weighted image (T2-WI). ?

1, MR signal generation? During the relaxation process, protons absorb the energy released by the combination of radio frequency pulses and produce magnetic resonance signals. By adjusting the imaging parameters TR and TE, MR signals which mainly reflect the contrast of T 1, T2 and PDWI can be obtained respectively, thus generating T- 1-WI, T2-WI or PDWI images.

High signal on (1)T- 1-WI? Subacute hematoma, high fat and protein content, melanin; ?

(2) Low signal on T-2wi? The contents of calcium, air, air, fat and protein are low. ?

2. Characteristics of magnetic resonance images

(1) multi-parameter gray image;

(2) Multi-directional tomographic images;

(3) Cavitation effect: the flowing liquid can't collect signals in the imaging process, so it appears as a shadow without signals;

(4) Enhancement effect of magnetic resonance contrast: As a contrast agent, paramagnetic materials can shorten the relaxation time of surrounding protons, which is called proton relaxation enhancement effect;

(5) Pseudo-color functional images. ?

3. Magnetic resonance examination technology

(1) sequence technology;

(2) Self-cyclotron wave sequence;

(3) gradient echo sequence;

(4) Reversing the recovery sequence;

(5) Plane echo imaging. ?

4.MR water imaging technology? With very long TR and very long TE, we can get very heavy T2-WI, which makes the static or slow-flowing liquid show high signal and other tissues in the background show low signal, thus forming a good contrast.

After recombination, organs or gaps containing liquid can show high signal, and images with similar contrast effect can be obtained, that is, MR water imaging, including MRCP, MRU, MRM and so on.

5. Clinical application

(1) brain and spinal cord diseases;

(2) hilar and mediastinal lymph nodes;

(3) the lumen of the great vessels of the heart;

(4) Diagnosis of breast cancer;

(5) Clearly show cartilage, joint capsule and other structures. ?

6. Preferred instrument for system inspection

(1) bones? Plain film is the first choice, and further CT;

(2) Magnetic resonance imaging of joints; ; ?

(3) the respiratory system? Plain film is the first choice, and further CT;

(4) Acute abdomen? Plain film is the first choice, and further CT;

(5) Closed abdominal injury? Ultrasound, CT;

(6) Esophageal lesions? Barium meal radiography; ?

(7) stomach and duodenum? Ultrasound and barium double contrast;

(8) liver? Ultrasound and c? T first choice, further MRI and hepatic arteriography can also be done;

(9) pancreas? Ultrasound and CT.

References:

Baidu encyclopedia-medical images