Comparative Study of Magnetocardiography and Emission Computed Tomography.

1. Research Background Magnetocardiography (MCG) is a non-invasive, risk-free, and contactless technology that characterizes the local magnetic field signals generated by the electrical activity of the heart. The magnetic signals from the heart and the electrical signals from the heart are of the same origin. The ionic activity within myocardial cells forms volume currents, and the curve representing the potential difference caused by these currents on the body surface over time is known as the Electrocardiogram (ECG). The spatial magnetic field changes caused by volume currents are referred to as magnetocardiograms. Magnetocardiograms are constructed by recording the magnetic signals of the heart using a multi-channel sensor array placed above the chest, thereby mapping the heart's magnetic field. By analyzing these magnetic maps, abnormal electrical activities of the heart can be detected, including myocardial ischemia, arrhythmias, and myocardial diseases. Traditional ECG detection technology is affected by various conductivities of human tissues and skin, whereas the magnetic signals used in magnetocardiograms can pass through the body with almost no interference. Therefore, magnetocardiography theoretically offers more clinically useful information, with the advantages of being non-invasive, safe, and fast, enabling earlier and more accurate diagnoses of potential heart diseases.Earlier magnetocardiography (MCG) systems were not adopted clinically because of their prohibitive costs and technical challenges.Recently,our country has successfully developed a heart magnetic measurement device based on spin-exchange relaxation-free magnetic measurement technology. This device has successfully completed 64-channel time-sharing heart magnetometry and 32-channel synchronous heart magnetometry.The core component of the heart magnetic detection device is the SERF atomic magnetometer, which uses a novel alkali metal atom operating in the SERF state to achieve extremely weak magnetic measurements. It has advantages such as non-cryogenic operation (traditional magnetometers require cooling with liquid helium), miniaturization, and high spatial resolution.The basic principle is: using high temperature to achieve a higher density of alkali metal vapor in the gas cell, suppressing spin-exchange relaxation, and using polarized detection light that is perpendicular to the pump light entering the gas cell to measure the Larmor precession frequency of spin-polarized atoms in a weak magnetic field, thus accurately reflecting the magnitude of the external magnetic field. The SERF magnetometer has achieved high sensitivity to low-frequency magnetic fields in weak magnetic fields.Therefore, MCG device can ultra-sensitively, non-invasively, and dynamically display human cardiac magnetic functional information, reflecting corresponding electrophysiological activities of the heart. It provides a novel tool for the clinical diagnosis and evaluation of cardiovascular diseases, holding broad application prospects in medicine.
2. Research Objectives This study aims to compare the domestically developed "ultra-sensitive" MCG device with ECT, the gold standard for myocardial ischemia detection, to determine whether the domestic "ultra-sensitive" MCG device can accurately identify myocardial ischemia, thereby exploring its clinical application value.
3. study design This study is a prospective, multi-center comparative study. 3.1 research contents 3.1.1 Recruit participants and collect data Patients who come to our hospital for treatment with myocardial ischemia symptoms such as chest tightness and chest pain and plan to undergo ECT will be informed by the receiving doctor of the clinical study. Patients who are willing to participate in the study will be further communicated with the patient by the investigator to evaluate and confirm whether they meet the inclusion conditions, and inform that the study will collect clinical diagnosis and treatment information such as basic conditions, medical history, laboratory examinations, as well as study-related precautions, and sign informed consent form.

3.1.2 Preparation before magnetic examination Before undergoing magnetic electrocardiogram, the patient's basic information was asked and checked, the past history, alcohol and tobacco status, and the current medical history (the onset time, inducement, symptom characteristics, duration, etc. of chest pain) were recorded, and the subject's blood pressure, height, and weight were measured.

3.1.3 Magnetocardiography and ECT examination MCG images were collected using a domestic "ultra-high-sensitive" MCG detection device, and ECG examinations were performed 10 minutes before and after. ECT examination was completed within 1 week.

3.1.4 Data Entry The subject's diagnostic results, myocardial damage markers, heart failure indicators, electrocardiogram, echocardiography, coronary CTA/angiography, ECT and other laboratory test results were recorded and entered into EDC.

3.2 Data Analysis The consistency of Magnetocardiographic results and ECT results was analyzed to evaluate the effectiveness of magnetocardiographic testing in early diagnosis of myocardial ischemia.

3.3 Sample size Estimation In this project sample size calculation was performed to ensure the statistical reliability of the study. By considering factors such as the expected effect size and significance level, an appropriate sample size was determined. This ensures sufficient support for testing the study hypothesis, guarantees scientifically credible results, enhances study reproducibility, and boosts data analysis robustness, thereby making the study conclusions more convincing and reliable.

For testing the non - inferiority of cardiomagnetic evaluation of myocardial ischemia compared to ECT, the sample size estimation used the method for comparing paired two - sample rates in a non - inferiority design and was calculated as follows:

n=(Zα+Zβ)2×(p1(1-p1)+p2(1-p2))/(p1-p2-Δ)2 In the formula： Zα is the critical value of the standard normal distribution; Zβ is the critical value of the standard normal distribution corresponding to the power; P1 and P2 represent the positive rates of the control group and the intervention group, respectively; Δ：non-inferiority margin; α：significance level; β：power of the test. The preliminary experimental results indicated a 77% positive rate for cardiomagnetic detection and 71% for ECT， with α=0.05 (one - sided), β=0.2 (power 80%), and Δ=0.05. We calculated the minimum sample size to be 196 cases, with a total sample size of 196 cases. Considering a dropout rate of 10%, the final determined sample size was 218 cases.

3.4 Statistical Methods Unless otherwise stated, the following general principles will be used for statistical analysis of the study data.

For categorical variables, statistical descriptions will be provided as the number and percentage of participants in each category. For continuous variables, the mean, standard deviation, median, Q1，Q3 and extremes will be listed. Diagnostic efficiency will be evaluated using sensitivity, specificity, AUC, recall, and F1 score for discrimination. Calibration will be assessed via calibration curves and the Hosmer-Lemeshow (H-L) test. Subgroup analyses will be conducted for rest ECT and stress ECT groups to compare diagnostic efficiency and consistency. The Pearson correlation coefficient will assess the linear relationship between cardiomagnetic scores and ECT ischemic areas, with the correlation coefficient (r) and significance level (p value) reported. The Kappa coefficient will evaluate the consistency of cardiomagnetic detection with rest and stress ECT in diagnosing myocardial ischemia, with the consistency level reported.

All statistical tests will use a significance level of 0.05.