Noun explanation summary - Micro CT (micro-X-ray tomography) related monitoring indicators

CT value

The CT value is the attenuation value of the water with respect to the X-ray of other substances. For example, the CT value of air is -1000, and the CT value of bone density is +1000. The CT value is basically between -100 and +100 except for the bone density and lung. The standard unit of CT values ​​is HU (Hounsfield). The higher the tissue density, the higher the CT value. If a tissue changes in density and changes in density, it will affect the change in CT value, which is of great value for CT diagnosis.

BMC

Bone Mineral Content (BMC) in g

BMD

Bone Mineral Density (BMD), the unit of 2D BMD is g/cm^2, and the unit of 3D BMD is mg/cc.

BMP

Bone Morphogenetic Protein (BMP) is a member of the transforming growth factor beta superfamily. It has the ability to induce the differentiation and proliferation of undifferentiated mesenchymal stem cells into chondrocytes and osteoblasts, and promote new bone. form.

BS

Bone Surface (BS) in mm^2

BS/BV

The ratio of bone surface area to bone volume in 1/mm.

BS/TV

The ratio of bone surface area to tissue volume in units of 1/mm.

BV

Bone Volume, in mm^3.

BV/TV

Relative bone volume or bone volume fraction in %.

Conn.D.

Connection Density (Conn.D.), the unit is 1/mm^3.

Ct.Ar

Cortical bone area (Ct. Ar), the unit is mm^2.

Ct.Th

Cortical bone thickness (Ct. Th) in μm.

Ct.Wi

Cortical bone Width (Ct. Wi) in μm.

DA

The Degree of Anisotropy (DA) is the ratio of the long diameter to the short diameter of the ellipse in the average intercept length of the ROI. In the early stage of osteoporosis, the DA of the load-bearing trabeculae usually increases, and as osteoporosis increases, DA decreases.

DICOM

Digital Imaging and Communications in Medicine (DICOM) is a digital medicine for the American College of Radiology (ACR) and the National Electrical Manufactorers Association (NEMA). Standard for image transfer, display and storage. In the DICOM standard, the format and exchange method of images and related information are defined in detail. With this standard, one can establish an interface on the imaging device to complete the input/output of image data. The DICOM standard is based on the industrialization standards of computer networks, which can help to transfer digital images between medical imaging devices more efficiently, including CT, MR, nuclear medicine and ultrasound, as well as CR and film digital systems. , video capture systems and HIS/RIS information management systems. The standard was produced in 1985 and the current version is the DICOM 3.0 2003 version released in 2003.

Distance Transformation

Distance transformation is one of the methods for quantitative analysis of trabecular bone, which calculates the distance between each voxel in the sample and the nearest bone-air interface (background). The calculated distance can be visually represented by a sphere centered on the voxel and having a radius. From the picture, the sphere is located inside the structure. During the calculation, the extra sphere is removed by replacing the inner small sphere with a large sphere. The Tb.N, Tb.Th and Tb.Sp calculated by this method are the most widely used. For details of the method, see the paper published by the University of Zurich, Switzerland: A new method for the model-independent assessment of thickness in three-dimensional images. J Microsc, 1997; 185:67-75

FOV

Field of View (FOV) is one of the important performance parameters of imaging equipment such as CT. It is used to measure the space size that an imaging device can effectively image.

HA

Hydroxyapatite (HA) is the main substance that makes up bones. Currently, a known density of HA is typically built into the phantom to calibrate the CT value.

HU

HU (Hounsfield Units) is a unit of CT value, named after the inventor of CT, Godfrey Newbold Hounsfield, and pronounced "Hu".

IPL

The Image Processing Language (IPL) is an advanced image processing language in SCANCO's MicroCT device software, written by SCANCO expert Andres Laib.

MAR

Mineral Apposition Rate (MAR) in μm/day.

MIL

Mean Intercept Length (MIL) is one of the methods for quantitative analysis of trabecular bone, which can calculate the intercept length of the test line inside the ROI. MIL is able to determine the ratio of surface area to volume (BS/BV) of the sample, which in turn estimates Tb.N, Tb.Th and Tb.Sp. The MIL distribution determines the degree of MIL ellipsoid and the degree of anisotropy (Degree of Anisotropy). For details of the method, see: Distribution of catalyst thickness determined by lineal analysis. J Microsc. 1978; 113:27-43.

MTF

Modulation Transfer Function (MTF) for evaluating the physical resolution of an imaging device such as a CT machine. Unlike the Normial Resolution or Detectability, the physical resolution expressed in MTF is an objective measure of the spatial resolution of imaging devices such as CT, expressed as 8μm@10%MTF (at 10% MTF level). The physical resolution is 8 μm).

OVX

Ovariectomy (OVX), an animal that has been ovarian-extracted (usually a rat or mouse) is used as an animal model of postmenopausal osteoporosis in women.

PACS

The Picture Archiving and Communication System (PACS) is a system for digitally collecting, storing, managing, transmitting and reproducing medical image information. Its main role is to replace the traditional film image recording, film and report warehouse storage, check the manual transmission of images, and reproduce the image on the light box. PACS makes full use of the characteristics of computers and networks, digitizes medical images, transmits them over a network, and reproduces images using display devices.

ROI

A Region of Interest (ROI) is a closed region defined in an image using a software tool, which typically has similar characteristics. The ROI defined in the 3D image is also called VOI (Volume of Interest).

Sham

Sham-operated, simulating the process of ovarian ablation, but retaining the ovaries as a negative control for the OVX animal model.

SMI

Structural Model Index (SMI), which defines the extent of trabecular plate-like and rod-like, and the SMI values ​​of slab trabecular and rod-shaped trabecular bone are 0. And 3. When osteoporosis occurs, the trabecular bone changes from a plate shape to a rod shape, and the SMI value increases.

STL

The STL format first appeared in the SLA rapid prototyping machine produced by 3DSYSTEMS in the United States in 1988. STL is the abbreviation of StereoLithography, which is a combination of the surface of a three-dimensional model expressed as a small triangle plane, very similar to the finite element. The three-node planar unit in the analysis.

Tb.N

Trabecular Number (Tb.N) refers to the number of intersections between bone and non-bone tissue within a given length, in units of 1/mm. When osteoporosis occurs, the value of Tb.N decreases.

TBPf

Trabecular Bone Pattern Factor (TBPf) measures the degree of convex and concave trabecular bone in 1/mm. . The low TBPf value suggests that the trabecular bone changes from a rod to a plate, and the TBPf value increases when osteoporosis occurs.

Tb.Sp

Trabecular Separation/Spacing (Tb.Sp) refers to the average width of the medullary cavity between the trabecular bone, in μm. An increase in Tb.Sp indicates an increase in bone resorption and osteoporosis may occur. In porous materials, Tb.Sp is understood as porosity.

Tb.Th

Trabecular Thickness (Tb.Th) refers to the thickness of the trabecular bone in μm.

When osteoporosis occurs, the Tb.Th value decreases. In porous materials, Tb.Th is understood to be the pore wall thickness.

TRI

Triangulation (TRI) is one of the methods for quantitative analysis of trabecular bone. The method represents the ROI surface in triangles of various shapes and sizes, and then calculates the volume of the internal tetrahedron of the ROI and the area of ​​the triangle. Using this method to calculate BS/BV is more straightforward than the MIL method, and it is also possible to estimate the direction and anisotropy of Tb.N, Tb.Th, Tb.Sp, and MIL ellipsoids. For details on this method, see the paper published by the University of Zurich, Switzerland: Direct Three-Dimensional Morphometric Analysis of Human Cancellous Bone: Microstructural Data from Spine, Femur, Iliac Crest, and Calcaneus. J Bone Miner Res. 1999; 14(7):1167 -1174.

VOI

See ROI

Surface reproduction

Surface rendering is a method of displaying a three-dimensional image of an object's surface. The advantage is that the amount of data required is small and the processing speed is fast. The disadvantage is that there is only a surface image and no internal structure information.

Partial volume effect

Voxels display an object discontinuously, so that the details in the object are evenly distributed, that is, the details in the voxel are expressed by a weighted average. This phenomenon is called partial volume effect and is used in CT imaging. Common image artifacts blur the edges of objects with large differences in density. The greater the layer thickness, the more serious the partial volume effect

Interpolation

Interpolation or interpolation is a method of mathematically estimating the value of a function at both ends of a function, estimating the value of either function between the two ends. The data acquired by the CT scan is discrete and discontinuous, and the function values ​​between them need to be obtained from two adjacent discrete values. There are many ways to interpolate, such as linear interpolation, rate over interpolation, and optimized sampling and scanning.

reconstruction

The raw scan data is processed by a computer using a specific algorithm to obtain an image that can be used for diagnosis. This processing method or process is called reconstruction. Image reconstruction speed is an important measure of CT machine performance

Reconstruction function kernel

The reconstruction function kernel (kernel) is also called reconstruction Filter and filter function. CT scans usually contain some necessary parameters, such as the voltage, current, and layer thickness of the tube. The reconstruction function kernel is one of the important contents. It is an algorithmic function that determines or affects the resolution and noise of an image. Common reconstruction functions have three modes: high resolution, standard and soft tissue: high resolution mode is a function that enhances edges and contours, which can improve resolution, but image noise increases accordingly; soft tissue mode is smooth, A softer function, reduced image contrast, reduced noise, and increased density resolution; standard mode is an algorithm without any enhancement or softening.

Reorganization

Reformation is an image processing method that does not involve raw data processing, such as multi-planar recombination, three-dimensional image processing, etc., that is, recombination or construction into a three-dimensional image based on a cross-sectional image. Since the formed cross-sectional image is used, the quality of the reconstructed image is closely related to the formed cross-sectional image.

window

The window is a different gray scale set by a computer according to the visual characteristics of the human eye. The setting of the window includes all about 4000 CT value ranges, which can be adjusted according to the needs of the human eye to suit the diagnosis needs. Window technology is usually adjusted by the window width and window level settings. The window width is represented by W (Width) and the window level is represented by L (Level) or C (Center).

Positioning scan

The Scout View is used to determine the initial sweep of the subsequent fine scan area.

Multi-planar reorganization

Multi-planar reformation (MPR) rearranges voxels and displays sections in any direction on a two-dimensional screen. A set of tomographic images acquired by CT are processed by computer to form three-dimensional volume data with the same distance between voxels, and then three-dimensional data (coronal, sagittal and cross-section) are used to intercept three-dimensional data to generate three images. Two-dimensional tomogram. The operator moves the position of the three planes with the mouse, causing the three images to undergo a coordinated change.

Resolution

Resolution includes spatial resolution, density resolution, and temporal resolution. The spatial resolution is the ability of the CT machine to distinguish two adjacent objects in high contrast. There are two representations of the line number (LP/cm) and the millimeter diameter (mm) per centimeter. The spatial resolution should be compared under the premise of 10% MTF. At present, the resolution of high-grade CT is around 15LP/cm (10% MTF). Density resolution is the ability of a CT machine to resolve two adjacent smallest objects at low contrast. The method is expressed as the percentage density difference of a certain object size, such as a 3 mm object with a density resolution of 3%, usually CT. The density resolution range is 0.25% to 0.5% / 1.5 to 3 mm. The time resolution is the number of frames that the CT machine collects images per unit time, indicating the dynamic scanning capability. In general, resolution refers to spatial resolution.

Separation

Separation refers to the process of dividing a complete three-dimensional volume image into several parts, as opposed to image combining.

Fourier transform

Fourier transform is a kind of image reconstruction method. It is a mathematical method for converting spatial signals into frequency signals. It can convert a spatial signal into sine and cosine functions with different frequencies and amplitudes.

Radiation dose

During the use of imaging equipment such as CT, both the operator and the animal to be examined need to pay attention to radiation protection. At present, there are several methods for measuring radiation doses:

l Exposure refers to the direct measurement of the amount of X-rays to air ionization, the intensity of the radiation field, and the intensity of the radiation from the perspective of the amount of charge. The unit is Coulomb?kg-1 (C?kg-1) or Roentgen (R);

l absorbed dose refers to the evaluation energy of any ionizing radiation absorbed by the irradiated substance per unit mass, and the amount of irradiation is reflected from the energy angle. The unit is Gy or Rad.

l dose equivalent, even in the case of the same absorbed dose, the biological effects of different radiation types are different, for the sake of comparison, the concept of dose equivalent is introduced. It uses an appropriate correction factor to weight the absorbed dose so that the corrected absorbed dose more reflects the degree of damage to the body. The unit is Sv (Sv) or Rem (rem).

Therefore, the dose equivalent (Sv) is more sensitive than the absorbed dose (Gy) or the amount of exposure (C?kg-1) to reflect the degree of X-ray damage of the CT machine to the human body. Normally, the natural environment radiates 1-10 mSv/year, the whole body CT scan is about 10 mSv/time, and the radiation received by a transoceanic aircraft is <5 μSv.

Ray tracing

In the process of medical image display, shadows and rays are usually used to enhance the stereoscopic effect of objects in a three-dimensional image. The most common method of applying light is ray tracing.

Gray scale

The gray level (scale) is a signal of a different brightness displayed on the image according to the CT value of the pixel. The gray level from white to black is divided into several levels, which is called gray level or gray level. The human eye generally only recognizes successive gray levels of about 40 levels, and the tissue density gray scale difference is much larger. In the CT image display technology, the window width and the window level are often adjusted by window technology to adapt to the optimal range of vision.

Parathyroid hormone

Parathyroid hormone (PTH) is a peptide hormone. Its main function is to affect the metabolism of calcium and phosphorus in the body. It acts on bone cells and osteoclasts to dissolve bone salts, mobilize calcium from bones, and make calcium in the blood. The ion concentration is increased, and it also acts on the intestines and renal tubules to increase the absorption of calcium, thereby maintaining the stability of blood calcium. If the secretion function of the parathyroid gland is low, the blood calcium concentration is lowered, and the hand and foot twitching occurs; if the function is hyperactive, the bone is excessively absorbed and the fracture is prone to occur.

matrix

A matrix is ​​an array of pixels arranged in two dimensions, related to the quality of the reconstructed image. In the same size sampling field, the larger the matrix, the more pixels, and the higher the image quality after reconstruction. Currently used matrix sizes are 512 x 512, 1024 x 1024 and 2048 x 2048.

convolution

Convolution is an important step in image reconstruction operation processing. Convolution processing usually requires the use of a filter function to correct the image, and after the convolution is finished, a new projection data for image reconstruction is formed.

American machinery

Engineers association

Founded in 1880, the American Society of Mechanical Engineers (ASME) is a non-profit international organization of education and technology that serves 125,000 members from around the world. Its publishing organization is one of the world's largest professional publishing organizations, developing a variety of industrial and manufacturing standards, such as the Journal of Biomechanical Engineering.

Reverse Engineering

The process of producing a model from an entity and then manufacturing it is usually called reverse engineering (RE). Standard reverse engineering is defined as: analyzing the target system, identifying the components of the system and their interactions, and presenting the process of the target system through high-level abstraction or other forms.

Registration

The process of registration is to seek a one-to-one mapping between two images, that is, to associate points in the two images corresponding to the same position in space. Image registration is often a prerequisite for image fusion (infusion)

Volume scan

Since the speed of the spiral CT is much faster than that of the non-helical CT, and the acquired data (volume acquisition section) of an organ is often used instead of one level of data, this scanning method is called volume scanning.

Volume reproduction

Volume rendering (VR) is a method of displaying a complete three-dimensional image of an object. Compared with surface reconstruction, the computer is more demanding, but retains the internal structure information of the object.

Soft ray

Soft ray energy is lower, easier to absorb for the human body, and is harmful to the human body, but has no effect in CT imaging. Hard ray energy is relatively high, most of which can directly penetrate the human body, the body absorbs less, and the harm is small. CT imaging mainly relies on hard X-rays. The wedge compensator or filter in the CT machine serves to block the soft X-ray and penetrate the hard X-ray. The multi-spectral X-ray generated by the tube is filtered into a uniform hard X-ray. The X-ray tube emitted by the tungsten target X-ray tube is called a hard ray. Relatively speaking, the X-ray tube made of a low atomic number anode target material such as molybdenum is called a soft ray. They emit longer X-ray wavelengths and have better penetrating power. Weak, high attenuation coefficient.

3D visualization

Due to the anatomical limitations of the human eye, humans cannot truly observe three-dimensional objects directly, and the three-dimensional images seen on the display screen are all generated by computer simulation of three-dimensional display effects. According to the Cartesian coordinate system of the X, Y, and Z axes, people can rotate the image arbitrarily in the direction of the three coordinate axes. With software processing, the three-dimensional projection images of the front, back, top, and bottom of the object can be seen. This three-dimensional display method is called 3D visualization in the terminology of image processing, and is called three-dimensional imaging in medicine.

algorithm

An algorithm is a set of rules for a particular input and output. The main feature of the algorithm is that there can be no fuzzy definitions. The steps of the algorithm rules must be simple, easy to operate and clear in concept, and can be implemented by computer.

extract

Segmentation refers to the separation of different regions of a particular meaning in an image. These regions do not intersect each other, and each region satisfies the consistency of a particular region. In image processing, segmentation is one of the methods of selecting a region of interest, usually by setting upper and lower thresholds, region growth, automatic edge detection, or defining a three-dimensional contour. This method is sometimes referred to as extraction.

Physique

A phantom is a standard used for calibration in an imaging device such as CT. The phantom of CT is usually composed of a plurality of hydroxyapatites of known different densities.

Voxel

In CT scans, the smallest volume unit that can be scanned by CT is called voxel, depending on the thickness of the fault setting and the size of the matrix. Voxels are represented by three elements: length, width, and height. They can arbitrarily represent the color, transparency, density, intensity, deformation, and time of an object. Corresponding to this is the pixel in a two-dimensional image.

Artifact

Artifacts are images that are caused by a device or patient and are not related to the scanned object. The shapes that appear in the image vary and affect the accuracy of the diagnosis. Artifacts such as motion artifacts caused by patient movement, radial artifacts caused by metal objects, radiation hardening artifacts caused by multi-spectral X-rays, partial volume effect artifacts caused by excessive layer thickness, etc.

Pixel

Pixel is the smallest unit that constitutes a CT image. Corresponding to the voxel, the size of the voxel on the CT image is the pixel.

Signal to noise ratio

The signal-to-noise ratio (SNR) is the ratio of signal to noise. Noise is included in any type of signal, but the ratio between signal and noise is different. In practical applications, the larger the ratio, the smaller the noise content and the higher the quality of information transmission.

Hard ray

See "soft ray"

Raw data

The raw data is the signal received by the detector after scanning the object, and is transmitted to the computer after analog-to-digital conversion. The part of the data that has been converted into a digital signal without image reconstruction is called original data.

Reproduce

Reproduction or three-dimensional rendering, a method of displaying a three-dimensional image in two dimensions, that is, displaying a three-dimensional isolated image on a display, which is realized by three main steps of image, inspection, and projection reconstruction, and has two types of surface reproduction and volume reproduction. algorithm. In order to increase the display effect, attributes such as light, shadow, texture and color can be added during the reproduction.

noise

In CT, noise is a random fluctuation of the CT value between points in a uniform material scanned image, and can also be regarded as an error caused by various factors in the image matrix.

Conical X-ray bundle

The cone beam means that the X-ray emitted by the bulb is irradiated onto the scanned object in a cone shape. Compared with the conventional fan beam, the cone beam CT has obvious advantages. 1) High data collection efficiency, high spatial resolution, good uniformity, (2) high X-ray utilization rate, can reduce radiation dose, and (3) wider application range in 3D CT. Although the reconstruction algorithm of cone beam CT is more complicated, due to its large amount of computation, with the rapid development of hardware and algorithms in recent years, medical and industrial CT are transitioning to medium or even large cone angle three-dimensional cone beam CT.

Maximum density projection

Projection is a common method of compressing three-dimensional information into two dimensions. The maximum intensity projection (MIP) projects the three-dimensional data in any direction. It is assumed that there are many projection lines, and the largest voxel value of all the voxels that the projection line passes is taken as the pixel value of the projection result image. Taking the minimum value on the projection line becomes the minimum density projection. The former is mostly used to display high-density shadows, such as angiography, while the latter mostly shows low-density shadows, such as airways.