myocardial perfusion imaging

Normal cardiomyocytes have the function of ingesting some imaging agents, and their uptake is directly proportional to myocardial blood flow, and the uptake or loss of ischemic or necrotic myocardium is manifested as a reduced or deficient region of myocardial segmental radioactivity. It is mainly used for the diagnosis of coronary heart disease, the choice of treatment plan, the judgment of curative effect and the prognosis evaluation. Basic Information Specialist classification: cardiovascular examination classification: ultrasound Applicable gender: whether men and women apply fasting: not fasting Tips: Stop the antiarrhythmia or slow down the heart rate before the test for 48h, and stop the nitrate drugs for 12-24h. Check the day to prepare fat meals, such as milk, fried eggs, etc. Normal value Myocardial perfusion SPEVT examination provides a tomographic image of the transverse, coronal, and sagittal planes of the myocardium. Clinical significance 1. Diagnosis of myocardial infarction or ischemic site, size and extent. 2. Differential diagnosis of abnormal Q wave of ECG. Precautions 1. Stop the antiarrhythmia or slow down the heart rate for 48 hours before the test, and stop the nitrate drugs for 12~24h. 2, check the day to prepare fat meals, such as milk, fried eggs and so on. Inspection process First, imaging agent There are three main types of myocardial perfusion imaging agents. 1, chlorinated 201 铊 [201TlCl]. 2. 99mTc-isonitrile compound, among which 99mTc-methoxyisobutyl isocyanide 99mTc-MIBI is the most widely used. 3. Other compounds labeled with 99mTc, such as 99mTc-labeled tetrofosmin (p53). Second, imaging equipment Planar imaging uses gamma camera imaging or SPECT, and tomography uses single- or multi-probe SPECT. Third, the imaging program There are differences depending on the radiopharmaceutical used. Currently, the more commonly used SPECT myocardial perfusion imaging protocols are as follows: 1, 201Tl exercise redistribution imaging method: intravenous injection of 201Tl92.5 ~ 111MBq (2.5 ~ 3mCi) at the peak of exercise, 5min early imaging, 3 ~ 4h after redistribution imaging, if you must judge the viability of cardiomyocytes, After re-distribution imaging, 74MBq was injected again, and resting imaging was performed after 5-10 minutes. 2, 99mTc-MIBI exercise resting every other day imaging: exercise peak injection 740 ~ 925MBq (20 ~ 25mCi), 1.0 ~ 1.5h imaging, every other day injection of 740 ~ 925MBq, 1 ~ 1.5h line resting imaging. 3, 99mTc-MIBI exercise resting imaging one day method: injection 296 ~ 333MBq (8 ~ 9mCi) at rest, 1 ~ 1.5h line resting imaging, 1 ~ 4h after exercise test and then injected 814 ~ 925MBq (22 ~25mCi), 1.0~1.5h imaging. 4, dual-nuclear imaging: intravenous injection of 201Tl74 ~ 111MBq (2 ~ 3mCi), 15min imaging, 60min exercise test, re-injection 99mTc-MIBI925MBq (25mCi), 1h after imaging. The program is mainly designed to overcome the shortcomings of the 99mTc-MIBI two-shot method, and the exercise and rest imaging can be completed within 2 hours. Fourth, the collection conditions 1, planar imaging: conventionally take the front and rear position, left front oblique 30 ° ~ 45 ° and left front oblique 70 ° position, if necessary, add left and right front oblique 30 °. The probe is equipped with a low-energy general-purpose or high-resolution collimator. The 201Tl peak can be 80keV. If there are multiple devices, the 167 and 135keV peaks can be added. The window width is 25%, the 99mTc peak is 140keV, and the window width is 20%. . The matrix is ​​128×128 or 256×256, each body position is collected for 10 minutes or the preset count is 5×105 to 6×105. The probe should be placed as close as possible to the body wall to improve resolution and sensitivity. 2, tomographic imaging: the subject takes the supine position, the upper arm holds the head and fixed, the probe is close to the chest wall, and the visual field includes the whole heart. The probe is rotated from the right front oblique position 45° to the left rear oblique position 45° rotation 180° or 360° acquisition. Each rotation is 3°~6° to collect 1 frame, 30~40s/frame, and collect 30~60 frames. The 201Tl and 99mTc energy windows are set to the same plane display, and the matrix is ​​64×64. The probe is equipped with a low energy universal or high resolution collimator. 3, gated myocardial imaging: 99mTc-MIBI image is better than 201Tl. Plane and tomographic acquisition methods are the same as above. Using ECG as the gate signal, the plane image is 8 to 16 frames per heart cycle, the RR window width is 15%, the matrix is ​​128×128, the tomogram is 8 to 12 frames per heart cycle, and the RR window value is 20%. The matrix is ​​64×64. Since each frame contains 8 to 12 points, the acquisition time should be significantly extended to ensure that the reconstructed image has enough counts to reduce the influence of statistical errors on the image. Fifth, image processing 1. Image reconstruction: At present, the processing software of most instruments uses the filtered back projection method to reconstruct the tomographic image. The selection of the filter function type and the cutoff frequency should be determined according to factors such as counting. The filters of various models can be different, and the reconstruction is short. The axial, horizontal long axis and vertical long axis cross-sectional images, each section thickness is generally 6 ~ 9mm. 2. Quantitative analysis of circumferential section: This method is performed on early imaging and delayed imaging, respectively. After the background subtraction, the image is multi-point weighted and smoothed. Taking the center of the left ventricular chamber as the midpoint, 60 sectors (6° for each sector) are generated, and the maximum value of the maximum count value of these sectors is 100%, and the relative percentage of the maximum count value of each sector is obtained. . Taking this percentage as the ordinate, the 360° circular diameter of the heart is plotted on the abscissa and plotted as a circumferential plane curve, which represents the relative radioactivity distribution of the various sectors of the myocardium. The peripheral imaging curves of the early imaging and the delayed imaging were coupled for comparison, and the elution rate of the delayed imaging 201T1 was calculated. Each unit must determine its own normal reference value. 3, polar coordinates bullseye map (Bull'seye): After reconstruction of the myocardial short-axis tomogram, the profile curve of each short-axis myocardial section is formed, and the peripheral section curves of the apex to the base section are arranged in a concentric manner, the center of the circle For the apex of the heart, the outermost layer of the circle is the base, that is, the bull's eye map. The percentage values ​​of each sector on the original bull's-eye map are compared with the normal percentage of the region, and the black-color map is displayed in black in the portion that deviates from the normal mean ± 2.5 or ± 3.0 standard deviations. It is suggested that myocardial perfusion in this area is abnormal. Using the bullseye map to show myocardial radioactivity distribution can assess the range of normal, reversible perfusion defects and fixed perfusion defects in a relatively objective and visual manner, and can quantitatively determine the percentage of left ventricular myocardium in the diseased myocardium. Sixth, gated tomography Three tomographic images of the short axis, the horizontal long axis and the vertical long axis are reconstructed, and each axial section can obtain 8 to 12 frames of images in each cardiac cycle. In image reconstruction, the axial end-diastolic and end-systolic 1-2 images can be superimposed into end-diastolic and end-systolic images, respectively, for easy reading. VII. Quantitative analysis of gated images The overall left ventricular function measurement and local wall motion assessment can be divided into the overall function such as left ventricular end-diastolic volume (EDV), end-systolic volume (ESV) and left ventricular ejection fraction (LVEF). Local wall motion can measure local myocardial thickening rate and direct observation of wall motion. Not suitable for the crowd It is not advisable to have myocardial perfusion imaging if the heart rate changes too much or the arrhythmia is frequent. Adverse reactions and risks May be concurrently infected.

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