Since ultrasound technology has been applied to clinical diagnosis for more than 60 years, with the development of clinical needs and modern electronic technology, especially computer technology, so that ultrasound imaging technology, from the early application of one-dimensional A and M-type ultrasound imaging developed to real-time grayscale two-dimensional B-type ultrasound imaging, to the current all-digital three-dimensional ultrasound imaging system that can be played back in real time. Ultrasound imaging has the advantages of non-invasiveness, high sensitivity, wide application, low cost and easy operation, etc. The speed of development and popularity has become the top of medical imaging in recent years. It can be expected that real-time three-dimensional (four-dimensional) ultrasound imaging will become one of the most effective diagnostic tools in the clinical application of medical imaging systems in the twenty-first century for the benefit of mankind.
It is because of this market demand that many well-known and visionary manufacturers around the world have invested in high-tech development of real-time 3D (four-dimensional) ultrasound imaging systems with all-digital technology. With a unique perspective, Neusoft Digital Medical Co., Ltd. has launched NAS-2000a, which has the world’s leading real-time 3D (4-D) technology and software technology, making ultrasound medical imaging perfectly combined with the contemporary cutting-edge computer technology, adopting the latest professional software for current clinical requirements, realizing dynamic 3D real-time playback and real-time 3D (4-D) imaging, simplifying the originally very complicated processing process and improve efficiency.
Principle and Method
Imaging principle: three-dimensional ultrasound imaging is divided into static three-dimensional imaging and dynamic three-dimensional imaging, dynamic three-dimensional imaging due to the addition of the time factor, with the overall imaging method to reconstruct the region of interest accurate real-time activity of three-dimensional images (also known as four-dimensional).
1, three-dimensional geometric composition method: the human organs assumed as a number of different forms of geometric combinations, requiring a large number of geometric prototypes, and thus for describing the complex structure of the human body is not fully suitable for three-dimensional form, is now rarely used.
2. Surface contour extraction method: A series of coordinate points in the three-dimensional ultrasound space are connected to each other to form a number of simple straight lines to describe the contour of the organs, which was used for the three-dimensional reconstruction of the heart surface. This technique uses less computer memory and faster movement. The disadvantages are: (1) it requires manual outlining of the tissue structure of the organ, which is time-consuming and subjective to the operator; (2) it can only reconstruct the left and right heart cavity structures, but not the small structures such as heart valves and tendons; (3) it does not have gray-scale features and is difficult to show anatomical details, so it is not adopted clinically.
3.Body element model method: It is the most ideal dynamic 3D ultrasound imaging technique, which can reconstruct all the tissue information of the structure.
In the voxel model method, the three-dimensional object is divided into small cubes arranged sequentially, and a small cube is a voxel. A certain number of voxels arranged according to the corresponding spatial location can constitute a three-dimensional image.
4, with the continuous development of high-grade ultrasound instrument software, three-dimensional imaging without a workstation can directly start the equipment package for three-dimensional reconstruction or three-dimensional film playback to complete. Imaging mode: dynamic three-dimensional ultrasound imaging principle and static basically the same.
1, surface imaging: extract the surface gray-scale information of the tissue structure, and then take the surface fitting approach to image reorganization.
2.Transparent imaging: The transparent algorithm is used to achieve 3D reconstruction, which lightens the gray-scale information of the tissue structure and makes it transparent, thus showing the spatial position relationship of the internal structure of the substantive organs.
Three-dimensional ultrasound reconstruction method
Image acquisition.
1.Mechanically driven sweeping.
Parallel scanning method: The probe is driven by an electric motor to acquire images at a predetermined speed and at predetermined intervals.
Rotational sweep method: The probe is fixed to a certain transmissive window and the probe is rotated around an axis to acquire images.
Fan sweep method: the probe is fixed at a certain position and driven by machinery to acquire images in a fan shape, with adjustable sweep interval angle.
2.Free arm sweeping method
3.Three-dimensional probe method: the chip is contained in a probe, and there is another mechanical device inside, which can drive the chip for equal distance fan or circular sweep.
4. Three-dimensional electronic phased array method
Three-dimensional reconstruction: the original images collected are stored after analog-to-digital conversion and the interval between images is interpolated and smoothed to form a three-dimensional database.
Clinical applications
I. Application in obstetrics
Two-dimensional ultrasound usually only performs cross-sectional observation of fetal structures, and thus has many shortcomings. 3D ultrasound can not only perform surface reconstruction of fetal body structure, but also 3D imaging of fetal body structure with transparent imaging, which can observe fetal shape and structure as a whole, improve the prenatal diagnosis rate of fetal malformation, and determine the normal and pathological morphology of fetuses of different gestational ages.
1. Imaging characteristics of fetal organs at different gestational ages
Detailed observation of 64 embryos and fetuses at different stages from 5 to 40 weeks of gestation was carried out. The results showed that the yolk sac could be shown at 5 weeks of gestation, the embryo was visible at the sixth week; and the primitive heart tube was clearly shown; the hand, fingers and toes could be identified at the eighth week; the open-mouthed fetus could be seen at 11 weeks; the male external genitalia could be identified at 12 weeks; and the upper and lower limbs and face could be completely shown at 13 weeks.
2. Pediatric biology measurement
To estimate the gestational week; to evaluate the fetal growth and development, to know whether there is intrauterine growth retardation (IUGR); to diagnose fetal malformation.
3.Fetal urogenital system
Through the parallel movement of the three planes of 3D ultrasound, diseases such as polycystic kidney and renal dysplasia can be clearly displayed. The 3D ultrasound surface imaging can visually and accurately display the three-dimensional morphology of the external genitalia of the fetus, which is of great value in determining the diseases such as hermaphroditism and scrotal cleft.
4. Fetal central nervous system
Many scholars have diagnosed neural tube malformation (anencephaly, cerebrospinal bulge, choroidal cyst, etc.) by 3D ultrasound imaging through a large number of clinical practice. 3D images established by using color multispectral information of blood flow can clearly show the structure of fetal cranial low Willis arterial ring, which is valuable for the determination of vascular malformation and other diseases.
5.Fetal abdominal wall defect
6.Fetal face
Fetal facial observation is an important part of ultrasound examination of high-risk pregnancy. Facial anomalies are usually an indication of chromosomal abnormalities or other fetal anomalies. While 2D only shows the forehead, eyes, nose, lips and ears, 3D provides a clearer view of the fetal facial anatomy and its interrelationships. Cleft lip and cleft palate are malformations that are difficult to identify using conventional 2D, and 10-15% of fetal cleft lip and cleft palate are associated with other malformations or chromosomal abnormalities. retorius et al. performed facial observation on 71 fetuses and the results could show 68 fetal facial lip structures, including 5 lip malformations. (Figure 4)
7. Skeletal development and malformations
It is easier to observe the continuity and curvature of the spine and thorax in 3-D than in 2-D, and it is possible to observe the abnormalities of the fetal spine and thorax from different angles to correctly diagnose scoliosis, vertebral defects, thoracic deformities and other malformations.
8.Fetal heart and blood vessels
Dynamic 3D images of the fetal heart may provide some helpful information for accurate estimation of ventricular volume and its dynamic changes, measurement of ejection fraction, and determination of complex congenital malformations of the fetal heart in utero, but compared with MRI 3D reconstruction of the fetal heart, it is still immature and the accuracy of measurement needs to be improved.
9.Umbilical cord
It can visually show whether the fetal umbilical cord has rapture (rapture body, rapture limb) extremely turns, visually show the winding and knotting of the umbilical cord, etc.
II. Applications in gynecology
1.Uterine diseases
The application of three-dimensional ultrasound imaging can obtain the echogenic information of the coronal plane that cannot be obtained by two-dimensional ultrasound, and can make a comprehensive analysis of the structure of interest through parallel movement and rotation in the mutually perpendicular plane, such as the judgment of uterine malformation, endometrial polyp, submucosal myoma, etc. has high value.
Uterine malformations: bowed uterus: curved concavity in the uterine cavity near the fundus;
Longitudinal uterus: the uterine cavity has a septum near the fundus and extends to the lower part of the uterus, but does not reach the cervix; if there is a cut at the bottom of the uterus, its depth must not exceed 1 cm.
Bicornuate uterus: images of the endometrium are seen independent of each other. There are two main indicators to distinguish the upper abnormality: the depth of the incision at the base of the uterus and the length of the intrauterine longitudinal septum.
Three-dimensional ultrasound allows easy and direct measurement of these two indicators, and can achieve quantitative criteria for the diagnosis of these uterine malformations. In the past, transabdominal or transvaginal ultrasound could not directly measure these two indicators. The sensitivity and specificity of 3D ultrasound for determining uterine malformations have been reported to be 100%, which is comparable to traditional hysterosalpingography, and has the advantages of being non-invasive and non-invasive.
Endometrial polyps and submucosal fibroids
Transvaginal ultrasound has improved the detection rate, but it is not easy to differentiate between them. Transvaginal 3D ultrasound increases the echo information in C plane, which can provide more help for the differential diagnosis of the two.
Endometrial cancer
The volume measurement method of 3D ultrasound can accurately measure the volume size of endometrial cancer, which is important for the diagnosis, staging and prognosis of endometrial cancer. Before the advent of 3D ultrasound, there was no method to accurately measure the volume of endometrial cancer. It has been reported that the sensitivity of endometrial volume greater than 13 ml as the criterion for endometrial cancer is as high as 100%, the specificity is 98.8%, and the positive prediction rate is 91.7%, which is significantly higher than that of endometrial thickness as the criterion for endometrial cancer by two-dimensional ultrasound.
2. Ovarian disease
★ 3D ultrasound can observe the internal structure of the cystic mass (whether the inner cavity is single, whether the inner wall is smooth, whether there is a septum, etc.);
For small papillae in cysts, 2D ultrasound can easily miss the diagnosis, while 3D ultrasound can visually show whether there are papillary protrusions on the inner wall and whether the morphology is regular through rotation, and can clearly observe the surface, size, number of papillae and the relationship with the cyst wall; when there are septa in the inner cavity, 3D ultrasound can clearly show the thickness of the septa, whether the surface of the septa is smooth, whether there is limited thickening, and whether there are redundant organisms on the surface, etc. If a cystic mass is found to have a blood clot inside and its surface is wrinkled, it is mostly a chocolate cyst; if there is a sandy sebaceous fluid, it is mostly a skin-like cyst; if there is a solid structure inside, the extent of the solid area and the surface morphology can be observed; a large extent, a wide base, and an obvious uneven surface are mostly malignant, and vice versa, it is benign.
★Three-dimensional ultrasound can visually display the spatial relationship between gynecological masses and peripheral organs such as bladder and rectum, and the infiltration range and depth of malignant tumors.
★The volume of ovarian tumor is one of the essential parameters for the determination of benignity and malignancy, indication for surgery and efficacy.
Bonilla-Musoles applied two-dimensional and three-dimensional measurement of tumor volume in 76 women with ovarian tumors, and also compared the tumor volume after surgery with the water replacement method.
3. Monitoring follicular development
3D can measure ovarian and follicular volume more accurately, clearly observe follicular boundary and fullness, accurately guide and monitor ovulation, guide clinical medication and treatment of infertility.
4.Intrauterine device (IUD)
It can clearly show the morphology, size and type of IUD, the accurate position in the uterus and abnormal implantation in the uterus.
III. Application in abdomen and small organ vascular imaging
1.The performance of normal organ three-dimensional images
(1) The vascular tree and its branches are fully displayed: The three-dimensional images show the branches of normal liver, kidney and spleen vascular trees from different angles, which are more complete and clear than the color Doppler blood flow imaging and energy map, with a sense of hierarchy from shallow to deep. It also shows the tiny blood vessels that are difficult to reveal in two-dimensional images, such as the renal arch artery and the fourth-grade branches of portal vein.
(2) The three-dimensional spatial structure of blood vessels is clear: the three-dimensional dynamic image is centered on the main trunk of the vascular tree, and the trunk to the end is imaged continuously, and single or multiple branches of the vascular tree appear from different directions, such as the right anterior lobe and the lower branch of the right posterior lobe of the portal tree correspond to each other, which has a more three-dimensional sense than the two-dimensional ultrasound. Local magnification of the vascular tree can clearly show specific details, such as the lobar arteries of the kidney, which are arranged symmetrically in a fish-spine pattern in the 3D angiogram. Two types of vessels, the portal vein and hepatic vein in the liver, and the 2nd, 3rd and 4th level branches of the kidney and spleen arteries, can be shown dynamically from the main trunk to the large branches and then to the small branches gradually; the branches of the two types of vessel trees are crossed or parallel to each other. The vascular trees of adjacent organs, such as the liver, spleen and two kidneys, are dynamically rotated at the same time with different levels of depth, setting off the three-dimensional anatomical relationship of adjacent organs, with the liver and spleen covering the upper pole of the kidney.
(3) Enhance the display of the vascular tree of small organs: normal small organs have small blood vessels with curved paths, which are only partially visible in 2D images;
After 3D reconstruction, a relatively complete vascular structure is formed. For example, the breast vessels are derived from the axillary artery on the outside, and the small branches of the internal mammary artery on the inside, and the blood flow is directed toward the nipple. The vascular tree of the normal thyroid gland and the central retinal artery of the fundus is clearer than that of 2D color Doppler ultrasound.
(4) Three-dimensional dynamic angiography: Three-dimensional reconstruction is a process of image superimposition, similar to the performance of contrast-filled vessels during X-ray angiography. The three-dimensional imaging starts from the arterial trunk, then branches to the terminal process like the arterial phase, and thickens from the terminal to the trunk like the venous phase, which is the three-dimensional dynamic angiography. In the pregnant uterus, the blood flow in the uterine artery and the placenta is seen to cross the placenta from the base into the umbilical cord.
2.The performance of the three-dimensional image of the diseased organ
(1) Multi-vessel tumor: Multi-vessel tumor of substantial organs, 3D image shows that malignant tumor such as liver cancer has more blood vessels, varying thickness and disorder, rich blood flow, thickened blood supplying arteries towards the tumor lesion, and surrounded by thick arterial and venous blood flow. Less vascular type carcinoma only has thickened blood supply arteries or blood flow encirclement, and the tumor itself is echogenically blurred.
(2) Hyperfunctional and hyperemic lesions: The 3D images of hypersplenism and hyperthyroidism show that the main trunk of the vascular tree is thick, with more branches and small terminal branches like a network. In contrast, hyperthyroidism with adenoma has a localized vascular filling defect. The vascular tree inside and outside the placenta of pregnancy increases with the time of pregnancy, and the vascular tree of uterus and placenta in late pregnancy is more than that in early pregnancy.
(3) Displacement, stenosis and interruption of the vascular tree: When the occupying lesion invades the vasculature, the three-dimensional image shows displacement of the vascular tree, abnormal orientation, or narrowing and thinning, and interruption of branches. The retroperitoneal tumor displaced, elevated, and compressed the superior mesenteric artery forward, and widened the distance between the vessel and the abdominal aorta. Three-dimensional images of multiple carcinoma thrombi in the portal vein show thin and narrow blood flow or interrupted blood flow.
(4) Less vascular and avascular type lesions 3D images have no characteristic or reduced vascularity: metastatic renal tumors have less vascularity on 3D images and form a relative contour of lesion size due to changes in the respiratory motion interface. Liver cysts are seen only as vessels in the surrounding tissues; fatty liver has reduced vascular branches that resemble dead branches. The performance of each lesion organ varies with the etiology of the pathology. The combination of history and clinical manifestations will improve the ultrasound diagnosis because it has a greater auxiliary value for ultrasound image analysis and differential diagnosis. The 3D angiographic manifestations of the diseased organs can be summarized as follows.
*Malignant multivessel type of substantial organs and infiltrating progressive tumors, with significantly increased and disorganized blood vessels at the lesion site.
*In hyperfunctional blood flow diseases, there is a chronic increase in vascularity in a reticular pattern, such as hyperthyroidism and hypersplenism.
The pathological nature of the lesion varies with the performance of 3D revascularization. For example, in liver cirrhosis with portal hypertension, the thickening of the vascular tree in the splenic hilum of the enlarged spleen is most obvious and gradually expands into the splenic parenchyma; whereas in leukemia-induced splenomegaly, the branching of the vascular tree increases, but there is no obvious thickening in the splenic hilum and splenic parenchyma, and the two diseases have different manifestations.
*In the case of multivessel organ or multivessel lesions, 3D vascular reconstruction shows vascular scarcity, thinning, narrowing, and atrophy, suggesting internal blood circulation disorders and blocked blood flow. For example, the 3D image of fatty liver shows reduced vascularity like dead branches, which is consistent with the thinning of hepatic veins in its pathology. In combination with benign oligovascular lesions, there is a localized vascular defect in the increased reticular pattern.
*When the lesion is large and invades a blood vessel, the three-dimensional image shows that the original vascular tree of the organ is compressed, thinned, or displaced, and that the direction and spatial structure are distorted or the branches are interrupted.
*If the lesion is small or the two-dimensional energy map shows poor vascularity, the three-dimensional image also shows poor vascularity.
Application in carotid artery and brain
Color Doppler flow 3D reconstruction of carotid artery can show the degree of carotid atherosclerosis in detail, such as the location, texture, attachment relationship, and carotid stenosis of plaque, which is useful for clinical assessment of atherosclerosis.
The application of 3D ultrasound in the cranial brain includes the localization of tumors and arteriovenous malformations and their proximity to the surrounding important structures. Intraoperative 3D ultrasound of cranial tumors can accurately show the size, extent and spatial relationship of tumors.
The biological characteristics of the eye and orbital diseases make it an ideal site for 3D ultrasound reconstruction. 3D ultrasound can clearly show intravitreal striae and membranous lesions, such as retinal detachment, intravitreal mechanization, vitreous inflammation, choroidal lesions, posterior dislocation of the crystal, etc. In case of retinal detachment, 3D ultrasound can visually show not only the starting and ending sites, size and extent of retinal detachment, but also the shape and number of retinal ruptures.
With the application of high-frequency ultrasound, three-dimensional ultrasound can also better display the lesions behind the sphere, and can accurately evaluate the relationship between the lesions behind the sphere (such as tumors) and the optic nerve and extraocular muscles of the eye, which is quite important for the surgeon to choose the appropriate treatment plan. Compared with MRI and CT, 3D ultrasound is more time-efficient, less expensive, non-radioactive, and can be repeated without fear of radiation-induced cataracts. In addition, 3D ultrasound can more accurately calculate the size and volume of the tumor and may make more precise localization of the lesion to guide the work of the surgeon and radiation therapist.
Genitourinary system
In patients with renal masses, especially solitary kidneys, whose surgical approach must preserve part of the kidney, it is critical to accurately describe the spatial relationship of the mass to the vascular tree, collecting system, and renal envelope. For imaging of the transplanted kidney, visualization of the local blood supply to the kidney by 3D ultrasound may establish a correlation between it and early rejection, as early changes in rejection may be segmental or partial. In addition, the determination of transplanted kidney volume and its changes over time may also be useful in the diagnosis of rejection.
Three-dimensional ultrasound shows bladder tumors in the form of cauliflower, papillae, or masses. It can show the spatial relationship between the tumor and the wall, the basal and surface conditions, and the number, size, orientation, and spatial relationship between the tumor and the ureteral opening can also be clearly shown. The volume of prostate tumor has an important significance to its prognosis. It is estimated that the metastatic volume of tumor will generally exceed 1.5cm3 , and most of the tumors with volume greater than 3.0cm3 will spread outside the prostate.