tomography

Tomography, abbreviated as CT, is a new imaging technology that combines X-ray scanning and electronic computers. Unlike traditional X-ray tomography, CT photographic images do not directly capture images on photographic film, but use X-rays to scan a certain layer of the human body, usually the transverse plane, through X-ray attenuation at the human level. The intensity is detected by the detector, the obtained information is amplified, converted into a digital by an analog-to-digital converter, input into an electronic computer for high-precision and fast arithmetic processing, arranged into a digital matrix, and the complex digital-to-analog converter constitutes an image. The matrix is ​​used to reconstruct the slice image of the inspection site. Basic Information Specialist classification: growth and development check classification: X-ray Applicable gender: whether men and women apply fasting: not fasting Reminder: For X-ray examination of infants and young children, it is best to expose only the part to be inspected, and the rest should be covered. Normal value The CT image has no abnormal pattern. Clinical significance Abnormal results: First, the brain CT examination indications and limits: (1) Craniocerebral injury: CT is easier and more reliable to determine intracranial hematoma and brain contusion. In the acute phase, intracranial hematoma is characterized by a uniform high-density lesion with a clear boundary, which can show the location, size and extent of the hematoma, and can be used to identify other brain damage. According to hematoma density and shape changes can be divided into 1. Acute epidural hematoma: manifested as a localized fusiform high-density area below the inner plate of the skull, with clear contact with the brain. The placeholder performance is relatively minor. 2. Acute subdural hematoma: manifested as a crescent shape under the inner plate of the skull, a thin layer of uniform high-density area. The shape of the subacute phase is constant, but mostly high or mixed density or equal density. Equal-density hematoma needs to be determined by displacement of the ventricles and sulci. Chronic hematoma is low in density and can also be of equal density. 3. Acute intracerebral hematoma: manifested as a round or non-plastic uniform high-density area in the brain, with a clear outline and cerebral edema around it. When it breaks into the ventricles or the subarachnoid space, high density shadows appear in the blood. 4. Brain contusion: A large, low-density edema area with clear boundaries and a patchy high-density hemorrhage. Simple brain contusion only appears as a low-density edema area with clear boundaries, occurring within a few hours to three days after injury, and most obvious for 12 to 24 hours, which lasts for several weeks. 5. Chronic subdural effusion: a low-density area resembling a cerebrospinal fluid in the crescent-shaped or half-moon shape below the inner plate of the skull. More common in the frontal area, involving one side or both sides, no or only a slight placeholder performance. Chronic subdural effusion is more common in brain trauma, and may be one of the manifestations of chronic subdural hematoma. (B) Brain tumor: CT quantitative diagnosis of brain tumor is quite reliable, qualitative is also better than other methods, third- and fourth-generation CT can also clearly show lesions with a diameter of not less than 0.5cm. According to the position of the developed lesion and the changes of the ventricle and cerebral cistern, it is not difficult to determine the location of the tumor. Combined with the reconstruction of the coronal and sagittal planes, the position of the tumor in three-dimensional space can be displayed, which makes the positioning diagnosis more accurate. Common tumors have typical CT findings, and qualitative diagnosis can be made in 70-80% of cases. For example, meningiomas are often characterized by high-density, well-defined, spherical or lobulated lesions that are connected to the skull or cerebellum or cerebral palsy. Significantly strengthened after enhancement. Brain metastases are mostly in the cortex and subcortical regions, showing small low, high or mixed density lesions. After enhancement, they are ring-enhanced or evenly enhanced. Multiple lesions are more important for diagnosis. In the saddle, low or mixed density lesions, most of which are enhanced by craniopharyngioma. Acoustic neuroma is a low or slightly high density lesion in the cerebellopontine angle region, which is enhanced, and the internal auditory canal enlargement and destruction can be seen. The characteristic signs of intracranial tumors are extensive edema around the tumor, and the displacement of adjacent brain structures and midline structures. Tumors located in the midline of the brain, especially in the posterior cranial fossa, can cause moderate to severe hydrocephalus even if the tumor is small. Atypical CT findings sometimes occur in common tumors, and some tumors may also show typical tumors. The CT diagnosis of intracranial tumors is limited. (c) cerebrovascular disease 1. Hypertensive intracerebral hematoma: CT findings are related to the stage of hematoma. The fresh hematoma is a high-density area with clear edges and uniform density. The CT value is approximately 50 to 70 HU. After 2 to 3 days, there was an edema around the hematoma. After about one week, the surrounding absorption density became lighter. After about 4 weeks, it becomes a low-density edge-softening stove. Hematoma occurs in the basal ganglia and thalamus, and the chance of breaking into the ventricles is higher. The hematoma breaking into the ventricle can buffer the increase of intracranial pressure caused by hematoma to varying degrees, but the intraventricular hemorrhage can also cause cerebrospinal fluid circulation obstruction, resulting in hydrocephalus and increased intracranial pressure. However, hydrocephalus caused by blood in the ventricles is rare. Intraventricular hemorrhage absorbs faster and faster than brain parenchymal hematoma, and completely absorbs and dissipates in more than one week. Www.med126.com 2. Cerebral infarction: Ischemic cerebral infarction occurs mostly in the middle cerebral artery supply area. The main occlusion of the arteries involves the cortex and medulla of multiple cerebral lobes. It is fan-shaped or wedge-shaped, with unclear boundaries and a placeholder performance. After the enhancement, there is a brain-like or patchy enhancement. Lacunar infarction caused by occlusion of terminal small arteries is more common in the basal ganglia and parietal radiographic crown, which is characterized by a clear low-density lesion with a diameter less than 1 cm and no mass effect. Hemorrhagic cerebral infarction is characterized by irregular, slightly high-density bleeding spots in large, low-density areas. 3. Arteriovenous malformations and aneurysms: Obviously CT diagnosis of arteriovenous malformations and aneurysms is not as reliable as MRI and DSA (digital subtraction). However, the diagnosis of CT is very accurate. In some cases, CT can also make a qualitative diagnosis. Aneurysms occur in the basilar artery or the communicating artery. The plain scan is slightly rounded and has a high density. The boundary is clear and there is no space-occupying effect. Arteriovenous malformations often showed spotted calcification in irregular low-density lesions, and there was no space-occupying manifestation. Enhanced scan showed obvious enhancement and abnormal enhancement around the lesion, and distortion of the vascular shadow. Aneurysmal malformation rupture can be seen in the subarachnoid space, brain or ventricle. (4) Degenerative diseases of the brain: brain atrophy. Diffuse brain atrophy is characterized by uniform symmetry expansion of the ventricles and pools, and widening of the sulci and fissures. Localized brain atrophy can exist alone, but most are manifested after certain diseases, or associated with certain diseases. Found in cerebrovascular disease atrophy. Alzheimer's disease, Alzheimer's disease, Pick's disease, subcortical arteriosclerotic encephalopathy, Hontingtons chorea, etc. (5) Inflammatory diseases: typical brain abscesses are characterized by a slightly higher density of the central density and a thinner wall. Regardless of the size of the abscess and the number of the abscess, it can be manifested as a wide area of ​​edema. Some brain tumors are characterized by atypical signs and are difficult to distinguish from brain tumors. In the acute encephalitis stage, it can only be expressed as an unclear low-density area of ​​the margin, which is not enhanced after enhancement, and is difficult to distinguish from other types of encephalitis. The CT manifestations of various types of encephalitis are non-specific, and are mostly manifested as a focal low-density area in a brain lobe or several brain lobe. The occupying performance is not obvious, and it is not enhanced after enhancement. The CT signs and cerebral infarction are not easy. Identification, combined with clinical ability to make a diagnosis. (6) Demyelinating disease: the symmetry of the white matter area around the lateral ventricle is slightly low-density plaque, the CT value is slightly higher than that of the infarct, and some of them can be fused into a sheet, no place-bearing performance, and the degree of cerebral atrophy. This sign is found in a variety of diseases, such as subcortical arteriosclerotic encephalopathy, Alzheimer's disease, multiple sclerosis, and the like. Low-density plaques of multiple sclerosis are also found in the basal ganglia, cerebellar hemisphere, and brainstem, and CT often does not. (7) Others: CT has diagnostic value for brain lesions with morphological changes, intracranial parasitic diseases, arachnoid cysts, and diseases with ventricular changes such as congenital brain abnormalities and brain atrophy. Second, spinal CT examination: (1) Degenerative changes of the spine: lesions can occur in the intervertebral disc space and on both sides of the posterior intervertebral joint. The examination range of each intervertebral space should be from the pedicle of the previous vertebral body to the pedicle of the next vertebral body, and the scanning plane should be parallel to the intervertebral space. The degenerative changes of the spine are more common in the lumbar spine and cervical vertebrae. The vertebral body hyperplasia, intervertebral disc herniation, posterior longitudinal ligament hyperplasia ossification, ligamentum flavum hypertrophy, posterior vertebral face hyperplasia. Degenerative changes in the lumbar spine are the most common. Early changes to the radial "tearing" of the annulus. Because the ring has not yet broken, resulting in a weak point, the nucleus pulposus in this area spreads around, although still contained in the posterior edge of the intervertebral disc, but can protrude to the weakest point, protruding from the thinned ring and the nucleus pulposus in the ring composition. When one or more tear waves and the posterior edge of the disc, a true rupture of the ring can occur, which can cause compression of nearby nerves. The posterior margin of the intervertebral disc is most common in the lateral deviation of the midline (posterior protrusion or sacral), or at the midline (central). The lateral rupture is the least common. There are two types of clinical syndromes that must be clearly distinguished. The first type is the cauda equina compression syndrome, which presents with back pain and is radiated to both lower extremities. The pain is aggravated when standing, and it is more dramatic when walking. Surprisingly, the neurological examination is negative. When walking is weak, it is bilaterally symmetrical, and the inhibition of deep tendon is also bilateral. The second type is the nerve root compression syndrome caused by the nucleus pulposus, which causes sciatica and may be associated with back pain. The pain is radiated along the affected nerve root pathway, which may be accompanied by the loss of sensory, muscular and deep tendon reflexes in the area of ​​the nerve root distribution. Positive leg elevation and positive Lasegue test also suggest that the nerve root is compressed. The nucleus pulposus is often compressed from the nerve roots in a flat intervertebral foramen of the ruptured disc. When the protruding disc fragments are large, the stern is also compressed, and there are two types of syndromes with clinical signs and feature. When the disc herniation is accompanied by spinal stenosis, there are two types of syndromes in the clinic. The CT findings of degenerative changes of the spine were: 1 posterior margin of intervertebral disc; 2 epidural fat displacement; 3 soft tissue density in epidural space; 4 dural capsule deformation; 5 nerve root sheath compression and displacement; 6 prominent nucleus pulposus calcification; 7 "vacuum" phenomenon in the intervertebral disc or osseous spinal canal (gas accumulation). (B) intraspinal tumors: between tumors and non-tumor lesions, between various types of tumors, and sometimes between tumors and normal tissues, CT values ​​are also lack of differential significance. However, significant differences in density are helpful for the identification of cysts, low-density tumors, high-density lesions, or calcification. Calcification or ossification of the tumor in the spinal canal is rare, but the condition of the spine bone is helpful for diagnosis. For example, metastatic lesions often have bone destruction, while erosion or piercing changes are seen in slow growth. Sexual lesions. Intramedullary tumors are characterized by widening or caliber of spinal cord segments, while extramedullary tumors are characterized by compression deformation and displacement of the spinal cord. Most tumors have no significant density difference with surrounding structures, even after venography. There is no difference in selectivity enhancement or iodine concentration, and it is necessary to assist diagnosis with metoclopramide myelography. (3) Spinal trauma: CT axial scan is suitable for diagnosing spinal cord compression, measuring the size of the spinal canal and whether there are fragments in the spinal canal. The common type of injury is "burst" of the vertebral body, vertebral arch fracture or disintegration. The spinal canal loses its normal shape. Spinal canal deformation and free bone fragments in the spinal canal cause compression and damage to the spinal cord. Spinal cord hemorrhage can be manifested as a high-density area with well-defined density, but spinal cord edema caused by trauma can not be shown, especially the trauma of spinal canal stenosis caused by degenerative spinal stenosis and idiopathic dysplasia, even There are no clear signs of fracture, but the symptoms of spinal cord injury are often more typical. This is because the already narrow spinal canal is highly susceptible to indirect laceration of the spinal cord when subjected to external impact. Although this type of injury shows very serious symptoms in the clinic, there are many abnormal findings (injury signs) in the CT scan. MRI is more reliable in this diagnosis, and this injury is more common in cervical vertebrae. (4) Others: Some congenital malformations of the spine and spinal cord, and the spine structure are well displayed on the CT film. People who need to be examined: people who need X-rays such as brain examinations and spine examinations. Precautions Taboo before inspection: X-rays have certain radiation and need to be mentally prepared. The number of exposures must not exceed 2 to 3 times. X-ray examination of infants and young children is best to expose only the part to be inspected, and the rest should be covered. Requirements for inspection: Obey the doctor's instructions to check. Don't have to panic on the X line. When the patient is on X-ray examination, the safe exposure should be within 100 roentgens, and the allowable number of exposures and time should be determined according to the exposure amount. Inspection process Lying flat under the CT instrument, undergoing CT examination. CT images are represented by different gray scales, reflecting the degree of absorption of X-rays by organs and tissues. Therefore, like the black-and-white image shown in the X-ray image, the black shadow indicates a low absorption region, that is, a low density region such as a lung; the white shadow indicates a high absorption region, that is, a high density region such as a bone. However, compared with X-ray images, CT has a high density resolution, that is, a high density resolution (densityresolutiln). Therefore, although the density difference of human soft tissue is small, although the absorption coefficient is close to water, it can be contrasted and imaged. This is a prominent advantage of CT. Therefore, CT can better display organs composed of soft tissues such as brain, spinal cord, mediastinum, lung, liver, gallbladder, pancreas, and pelvic organs, and display images of lesions on the background of good anatomical images. Not suitable for the crowd Pregnant women. Adverse reactions and risks No complications.

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