What Is a SPECT Scan?

Single-Photon Emission Computed Tomography (SPECT) and Positron Emission Tomography (PET) are two types of CT technology in nuclear medicine. X-ray imaging is collectively called Emission Computed Tomography (ECT).

Chinese name: Single photon emission computed tomography

Foreign name: Single-Photon Emission Computed Tomography, SPECT

SPECT imaging principle

The basic imaging principle of SPECT is: First, the patient needs to ingest a radioisotope drug containing an appropriate half-life. After the drug reaches the fault location to be imaged, due to radioactive decay, gamma photons will be emitted from the fault, and the gamma camera located in the outer layer Each sensitive point of the probe detects the gamma photons coming in along a projection line (Ray). The scintillator converts the detected high-energy gamma rays into a light signal with a low energy but a large number. The photo signal is converted by a photomultiplier tube. It is an electric signal and is amplified, and the obtained measurement value represents the sum of human body's radioactivity on the projection line. Sensitive points on the same line can detect radiopharmaceuticals on a fault in the human body, and their output is called the one-dimensional projection of the fault. Each projection line in the figure is perpendicular to the detector and parallel to each other, so it is called a parallel beam. The intersection angle between the normal of the detector and the X axis is called the observation angle (View). A gamma camera is a two-dimensional detector. When a parallel-hole collimator is installed, it can acquire parallel beam projections of multiple faults at the same time. This is a flat film. The flat film does not show the anteroposterior relationship of the points on the projection line. If you want to know the structure of the human body in the depth direction, you need to observe from different angles. It can be proved that knowing the one-dimensional projection of a fault at all observation angles can calculate the image of the fault. The process of solving tomographic images from projections is called reconstruction. This type of tomography is inseparable from the computer, so it is called Computed Tomography (CT). The main function of a CT device is to acquire projection data and reconstruct tomographic images.

Main clinical applications of SPECT

Because the imaging of SPECT is not clear enough, single SPECT imaging is gradually replaced by SPECT / CT. SPECT / CT has become one of the most advanced medical imaging equipment in human beings at present, and it is an ideal tool for diagnosis of living diseases and research and development of new drugs. ^[1]

Advanced medical equipment uses the SPECT principle to measure and display biological activities of cells and molecules. For example, the SPECT system of GE Corporation, combined with diagnostic multi-layer CT composite imaging equipment SPECT · CT and PET · CT systems, can accurately locate the Location, nature and extent. SPECT imaging has an important role in the clinic. It can be used for tomography detection in the following aspects to obtain three-dimensional stereo images.

SPECT bone imaging

Bone imaging is the preferred method for early diagnosis of bone metastases from malignant tumors. It can be used for disease staging, bone pain evaluation, prognosis judgment, efficacy observation and detection of dangerous parts of pathological fractures.

SPECT cardiac perfusion tomography

Diagnosis of myocardial ischemia. Can evaluate the extent of coronary artery disease and grade the risk of coronary heart disease; evaluate changes in myocardial blood flow perfusion caused by coronary stenosis and the function of collateral circulation, evaluate myocardial cell viability; evaluate the prognosis and efficacy of myocardial infarction; observe the heart Improvement of myocardial ischemia after bypass and interventional therapy.

Diagnosis of myocardial infarction, diagnosis of myocardial infarction with ischemia, and judgment of myocardial cell survival.

Differential diagnosis of cardiomyopathy and ventricular aneurysm.

SPECT thyroid imaging

Diagnosis and localization of ectopic thyroid. Has unique value.

Judgment of thyroid nodule function and benign and malignant differentiation have high diagnostic value.

Localization and diagnosis of well-differentiated thyroid cancer metastases.

Estimate of thyroid size and weight.

SPECT local cerebral blood flow tomography

Diagnosis of ischemic cerebrovascular accident. It has high diagnostic value.

Localization diagnosis of epileptic focus. The positive rate between seizures is as high as 60% (while XCT and MRI are about 25%).

Judging the blood flow of brain tumors, identifying recurrence and scarring after or after radiotherapy.

SPECT renal dynamic imaging and nephrogram examination

Understand renal artery disease and blood supply to both kidneys; judge renal function and subrenal function; understand upper urinary patency and diagnosis of urinary tract obstruction; monitor blood perfusion and function of transplanted kidney; and understand diabetes Functional impact. The main clinical applications of other imaging

Parathyroid imaging: diagnosis and localization of parathyroid adenomas.

Adrenal medulla imaging: diagnosis and localization of pheochromocytoma and its metastases, and follow-up after treatment with malignant pheochromocytoma 131I-MIBG.

Pulmonary perfusion imaging and pulmonary ventilation imaging: diagnosis and efficacy of pulmonary thromboembolism.

Hepatic colloid imaging, hepatic blood flow, and hepatic blood pool imaging: diagnosis of hepatic cavernous hemangioma.

Hepatobiliary dynamic imaging: used to distinguish obstructive jaundice and hepatocellular jaundice; identify congenital biliary atresia and infant liver syndrome and observe the effect.

Intestinal bleeding imaging: best for detecting active lower gastrointestinal bleeding below the stomach and above the sigmoid colon.

Ectopic gastric mucosal imaging: diagnosis and localization of Meckel's diverticulum, differential diagnosis of intestinal obstruction or intussusception (suspected to be related to Meckel's diverticulum or repeated small bowel malformations)

Salivary gland imaging: a common method to understand the function of salivary gland uptake, secretion, excretion, and presence or absence of occupying lesions.

SPECT early diagnosis of Alzheimer's disease

Foreign scholars use SPECT to study the local cerebral blood flow perfusion of Alzheimer's disease (AD), and then evaluate the local brain function in the 1980s. Although the methods and results are different, the characteristics of AD Sexual change has reached a consensus.

When comparing the results of SPECT and CT in the diagnosis of AD, it was found that the diagnosis of brain atrophy by CT is almost universal, and there is a lack of a clear operational boundary between light and severe atrophy, physiological and pathological. Foreign studies often use three-dimensional quantitative data of cT, such as measuring the volume of frontal, temporal, and parietal lobes, or measuring the distance of key parts such as the sulci and hippocampus, while domestic studies only use two-dimensional CT images to diagnose with naked eyes. This method is too crude and poor in reliability. If 3D CT technology can also be promoted in China, the value of CT for AD diagnosis will be greatly enhanced. SPECT can identify two types of dementia with similar levels of dementia and cognitive status. ^[2]