Lumbar disc herniation is a common clinical disease and imaging plays an important role in its diagnosis, which is outlined in this paper in terms of different imaging diagnoses of lumbar disc herniation. The most common sites of lumbar disc herniation are L4-5 and L5-S1, and the rest are rare. The signs seen on plain radiographs are as follows: 1. Spinal space narrowing, either symmetrical or asymmetrical. When it is not symmetrical, the side with the wider gap is mostly the side with the herniated disc. 2, vertebral body edge bone superfluous formation, this condition is not of special diagnostic significance, because the bone superfluous in hypertrophic spondylitis more common. 3, abnormal physiological curvature of the spine (lateral film), or the presence of scoliosis (orthogonal film). The nucleus pulposus protrudes into the vertebral body: The nucleus pulposus protrudes through the damaged rupture of the cartilage disc into the osteophytes of the upper and lower vertebral bodies, forming an indentation on the edge of the vertebral body the size of a soybean or broad bean, called a Schmorl’s node. x-ray shows a well-defined trap-like cut on the upper and lower edges of the vertebral body. The bone at the edge of the defect is often sclerotic and whitened. In severe cases of nucleus pulposus protrusion, the vertebral space may become narrow. 5, the canal or intervertebral foramen free bone block shadow; 6, dynamic X-ray examination (hyperextension and hyperflexion position) can determine the segmental instability. Although the frontal and lateral x-ray of the lumbar spine can show the vertebral body, the intervertebral space and the physiological curvature of the lumbar spine as a whole, this can only indicate the occurrence of lesions, but cannot confirm the diagnosis of whether it is caused by a herniated disc or by diseases such as tuberculosis or tumor, and even more so, it cannot accurately diagnose the situation of nerve root compression by a herniated disc. Therefore, the accuracy of diagnosing the disease by X-ray alone is not high. Studies have found that the accuracy of X-ray diagnosis of lumbar disc herniation is only about 42%. At the same time, the low resolution of X-rays makes the diagnostic rate of X-rays for lumbar disc herniation low, however, X-rays can present the level of disc herniation and provide reference for further examination by other methods. Second, myelography The injection of positive or negative contrast agent (referring to air) into the subarachnoid space to observe the state of the tissue around the spinal cord and dural sac and any abnormalities seen through X-ray examination is called myelography. 1, the choice of contrast agent: ① in the past the application of contrast agent: iodine stupid ester, 60% CONRAY (Conray), air (negative contrast agent) is now basically eliminated. ②Contrast agents applied now: non-ionic iodine contrast agents such as OMNIPAQUE and ISOVIST, and the latter is the most widely used and the safest. 2.Contrast method: The patient lies on his side on the X-ray examination bed, with the affected side underneath. The skin of the lumbar back is sterilized and a lumbar puncture is made in the L3, L4 or L4, L5 intervertebral space to access the subarachnoid space. The appropriate amount of cerebrospinal fluid is withdrawn before injecting the contrast agent, which should be done slowly. Contrast medium (Isohexan) is then injected. Observe the flow of the contrast agent in the subarachnoid space under X-ray TV, and spot films (orthogonal, lateral and, if necessary, oblique films) promptly when lesions are found. 3. Contrast performance ① Posterior median protrusion: the contrast agent at the level of the intervertebral space shows anterior edge invagination in lateral films, which is the indentation of the protruding disc, with a depth of 2 mm. larger posterior median protrusions and often compress the nerve roots. (ii) Posterior lateral protrusion; orthogonal and oblique views show unilateral lateral indentation of the contrast column with deflection of the nerve root sheath cuff, elevation or truncation, and thickening of the nerve root due to edema. (iii) Lateral protrusion, deflection, displacement or truncation of the nerve root sheath sleeve only, and no morphological changes in the dural sac. L5-S1 disc herniation may be missed. Myelography was commonly used before the 1980s, but has largely replaced myelography since the 1980s due to the introduction of CT and MRI. 4, discography Park et al. proposed the concept of discogenic low back pain (DLBP) in 1979, and discography is now considered the gold standard for the diagnosis of DLBP. However, there are still many controversies regarding discography. Most of these controversies are related to the false-positive rate of discography. Therefore, the pressure of the imaging and the morphological manifestations of the disc need to be examined. According to Adams et al. the morphology of discography is classified as follows: type I, cotton ball; type II, lobulated; type III, irregular; type IV, torn; and type V, ruptured. The morphology of contrast is important for the analysis of contrast results The International Society for the Study of Pain classifies the contrast-induced results into three categories: (1) consistent pain, i.e., low back pain of exactly the same nature, degree, and location as the patient’s usual; (2) non-consistent pain, i.e., the induced low back pain is somewhat different from the nature, degree, and location of the patient’s usual low back pain; and (3) no pain, i.e., the injection of contrast agent did not induce any low back pain. Han Yue et al. found that the more severe the rupture of the disc, the lower the pressure required to induce pain, and vice versa, the higher the pressure, when imaging at different pressures. This suggests that the degree of disc fibrous ring rupture directly affects the pressure at which the imaging is to induce consistent pain. Although discography has some value in clinical diagnosis, this method is less commonly used nowadays because it may cause damage to the intervertebral disc annulus fibrosus. CT CT is a clinical imaging means for lumbar disc herniation, with the advantages of fast scanning speed and relatively low price, which has certain advantages for the diagnosis of lumbar disc herniation. CT scan can not only clearly observe the transverse section of vertebral body, spinal canal and accessories, but also has sympathetic discrimination ability to different tissue levels. CT can directly show the site, morphological size, edge, density, calcification, ossification of lumbar disc protrusion, slippage of protruding nucleus pulposus, fragmentation and its relationship with the periphery, and also can show the hyperplasia and degeneration of lumbar spine accessories, hypertrophy or ossification of ligamentum flavum, compression of nerve by disc protrusion, lateral saphenous fossa and so on. CT can accurately make the diagnosis of intervertebral disc lesion gap, protrusion direction, protrusion size, nerve compression and main symptom causing site. (1) Lumbar disc degeneration and bulge: degenerated and degenerated lumbar discs can produce nitrogen, the so-called vacuum phenomenon, and the CT value is negative. In the CT image lumbar disc bulge is manifested as a uniform smooth symmetrical soft tissue density shadow beyond the edge of the vertebral body, with an intact contour whose posterior edge is depressed and may also bulge. The anterior edge of the dural sac is flattened, or there is a shallow indentation. (2) Lumbar disc herniation: there are three types. (1) Central type, referring to those located in the midline. (2) Lateral posterior type, referring to those located in the spinal canal on both sides of the midline. (3) Lateral type, the center of the herniated disc is located outside the spinal canal, and this type has heavy nerve root compression symptoms. CT has high spatial resolution and density resolution, which can directly and clearly show the morphology of the disc and its relationship with the dural sac and nerve roots, and usually the diagnosis can be confirmed by CT examination and medical history. However, the diagnosis of lesions such as lateral saphenous fossa and nerve roots by CT plain scan is vague, and the diagnosis of patients with severe deformity, congenital spinal stenosis, and postoperative spinal canal has some difficulties. However, for free type lumbar disc herniation CT often misses the diagnosis, therefore, when there is clinical suspicion of lumbar disc herniation and there is no herniation in the conventional scan, CTM continuous scan is performed at the upper or lower edge of the intervertebral space 10-20 mm at the plane of nerve compression, and the section finds that there is a nucleus pulposus connected with the tip and protruding at the upper and lower edge of the vertebral body free in the spinal canal, which is a reliable basis for free type disc herniation. At the same time by the machine performance, scanning methods and other hard, CT examination still has a certain rate of misdiagnosis. 2.CT image manifestation of lumbar disc herniation (1) Direct signs: ① Soft tissue shadow of the posterior edge of the lumbar disc protruding into the spinal canal in a restricted manner. The density is consistent with the density of the corresponding lumbar intervertebral disc, with different morphology and regular or irregular margins; ② the protruding lumbar intervertebral disc may have different size and morphology or calcification; ③ the free nucleus pulposus fragments can be seen in the epidural space of the spinal canal, and its density is higher than that of the dural sac. (2) Indirect signs: ① displacement, narrowing or disappearance of the epidural fat space; ② displacement of the dural sac and nerve roots by compression; ③ bone changes due to the disc: reactive osteosclerosis around the prolapsed nucleus pulposus with variable and irregular morphology, mostly on the posterior surface of the spinal canal; ④ Schomorl’s nodule, which is more clearly shown on CT than on plain film. CTM can clearly show the soft tissue structures around the lumbar spine, spinal canal, intervertebral disc, lateral saphenous fossa and small joints, especially to make a definitive diagnosis of disc herniation, and the typing of disc herniation is clearer than CT plain scan. It can confirm the diagnosis of displacement, deformation, swelling and thickening of nerve roots. MRI Compared with CT, MRI is not radioactive. MRI can show various signs of lumbar disc herniation more accurately and clearly: 1. disc bulge: sagittal view shows smooth edge of the disc bulging backward, the corresponding anterior edge of the dural sac is mildly compressed, more obvious on T2W1-weighted image, transverse view shows symmetrical extension of the disc to the periphery, beyond the edge of the adjacent vertebral body, the dural sac and both sides of the intervertebral foramen are mildly compressed; 2. disc herniation: sagittal view shows The intervertebral disc is confined beyond the edge of the adjacent vertebral body and protrudes into the spinal canal, with isosignal T1W1 and low signal T2W1. The corresponding anterior edge of the dural sac is deformed by compression, and there is obvious depression, and the soft tissue shadow of the disc protruding into the spinal canal is seen posteriorly or laterally in the transverse view; 3. The signal is the same as that of the original disc, and the signal is the same as that of the original disc. MRI shows high soft tissue resolution and contrast, non-invasive, non-ionizing radiation, good differentiation of intervertebral disc, vertebral body, fat, ligament, nerve root, dural sac, spinal cord, cerebrospinal fluid, etc. It is very sensitive to signal changes of the lumbar intervertebral disc, and multi-directional imaging such as sagittal, transverse and coronal can clearly show the site, direction, degree, morphology of the herniated disc, and its dural sac, nerve root, spinal cord and other pressure, and multi-parameter and multi-sequence imaging can Multi-parametric and multi-sequence imaging can obtain different contrast images, and special imaging such as fat suppression can identify fat and non-fat components, providing clinicians with rich imaging information, which is important for the development of treatment plans, preoperative positioning and surgical methods. Sagittal imaging can reduce missed and misdiagnosed high-grade disc herniations due to the greater extent of display, especially free discs. MRI is the best imaging method for diagnosing lumbar disc herniation. A lumbar disc herniation is not the same as a lumbar disc herniation, and a lumbar disc herniation demonstrated by MRI does not necessarily constitute a lumbar disc herniation. In fact, the diagnosis of lumbar herniation relies on medical history and signs. Magnetic resonance myelography (MRM) has some value in diagnosing nerve root compression. MRI can show nerve root compression well and has better display ability than MRI, which has high value in confirming and excluding responsible discs in patients with lumbar herniated discs. V. Far-infrared thermography The clinical application of infrared thermography began in 1956 for the diagnosis of breast tumors, and was officially approved as an auxiliary diagnosis for breast tumors in 1982. Because of its non-invasive and non-contact characteristics, it has recently been widely used in the diagnosis of inflammation and pain, clinical auxiliary diagnosis of tumor, cardiovascular, cerebrovascular and peripheral vascular lesions, efficacy observation and follow-up, and clinical research. Unlike structural imaging such as CT and MRI, infrared thermography belongs to the category of functional imaging. It was found that the infrared thermographic changes in patients with lumbar disc herniation had a high rate of agreement with the clinical manifestations and the diagnosis of CT, MRI and other imaging examinations. Lumbosacral radiculopathy is closely related to its clinical manifestations and MRI images, which can be used as a diagnostic basis for lumbosacral radiculopathy. The far-infrared thermogram of lumbar disc herniation shows an abnormal hot area in the lumbosacral region, which is rhombic or pike shaped and may appear as a sheet of uniform red color, and sometimes a dark red hot area may appear within the red hot area, and it is mostly biased to the affected side. It is considered that the herniated disc causes aseptic inflammation of the nerve root and its surrounding tissues, local inflammatory material infiltration, microvascular dilation, increased blood flow rate, and increased local temperature, causing an increase in the temperature of the skin area of the corresponding segment. In addition, local inflammatory material stimulation and pain caused by nerve root compression can cause local muscle tension and spasm, and enhanced metabolism, which can also increase the body surface temperature. The far-infrared thermographic manifestation of lumbar disc herniation corresponds to the anatomical features of lumbar disc herniation. The more extensive the thermal zone and the higher the local temperature, the more severe the inflammatory changes caused by the herniated disc and the more severe the impact on the nerve roots. Far-infrared thermogram visually reflects the distribution range of abnormal thermal zone of lumbar disc herniation and quantitatively detects the temperature change of abnormal thermal zone, which can be used as a functional index for the diagnosis and efficacy assessment of lumbar disc herniation. However, the specificity of its diagnostic value has yet to be further explored. In conclusion, there are many imaging diagnostic methods for lumbar disc herniation in clinical practice, and each method has its own advantages and disadvantages, which must be reasonably selected according to the purpose of observation, and the combination of multiple methods can improve the accuracy of diagnosis and reduce the rate of misdiagnosis. Imaging of lumbar disc herniation must also be combined with clinical examination. the application of modern diagnostic techniques such as CT, CTM and MRI has provided a more objective basis for the diagnosis of lumbar disc herniation. However, there should not be over-reliance on their clinical significance to avoid making the mistake of expanding the diagnosis. X-ray and CT alone showing osteophytes, disc herniation or bulging at the posterior edge of the vertebral body obviously cannot fully diagnose this sign. If CTM and MRI reveal the presence of nerve root compression, the diagnosis cannot be established either. If there is a lumbar disc herniation or bulge on the imaging and there is a lack of corresponding clinical symptoms or signs, blind surgery will not only be ineffective but will increase the patient’s pain.