Zhang John, Toftness Dave, Snyder Brian, Nosco Dennis, Balcavage Walter, Nindl Gabi
Logan College of Chiropractic, Chesterfield, MO 63006-1065, USA.
J Can Chiropr Assoc. 2004 Dec;48(4):273-81.
The use of magnetic fields to treat disease has intrigued mankind since the time of the ancient Greeks. More recently it has been shown that electromagnetic field (EMF) treatment aids bone healing, and repetitive transcranial magnetic stimulation (rTMS) appears to be beneficial in treating schizophrenia and depression. Since external EMFs influence internal body processes, we hypothesized that measurement of body surface EMFs might be used to detect disease states and direct the course of subsequent therapy. However, measurement of minute body surface EMFs requires use of a sensitive and well documented magnetometer. In this study we evaluated the sensitivity and frequency response of a fluxgate magnetometer with a triaxial probe for use in detecting body surface EMF and we compared the magnetometer readings with a signal from a Toftness Sensometer, operated by an experienced clinician, in the laboratory and in a clinical setting.
A Peavy Audio Amplifier and variable power output Telulex signal generator were used to develop 50 microT EMFs in a three coil Merritt coil system. A calibrated magnetometer was used to set a 60 Hz 50 microT field in the coil and an ammeter was used to measure the current required to develop the 50 microT field. At frequencies other than 60 Hz, the field strength was maintained at 50 microT by adjusting the Telulex signal output to keep the current constant. The field generated was monitored using a 10 turn coil connected to an oscilloscope. The oscilloscope reading indicated that the field strength was the same at all frequencies tested. To determine if there was a correspondence between the signals detected by a fluxgate magnetometer (FGM1) and the Toftness Sensometer both devices were placed in the Merritt coil and readings were recorded from the FGM1 and compared with the ability of a highly experienced Toftness operator to detect the 50 microT field. Subsequently, in a clinical setting, FGM1 readings made by an FGM1 technician and Sensometer readings were made by 4 Toftness Sensometer operators, having various degrees of experience with this device. Each examiner obtained instrument readings from 5 different volunteers in separate chiropractic adjusting rooms. Additionally, one of the Toftness Sensometers was equipped with an integrated fluxgate magnetometer (FGM2) and this magnetometer was used to obtain a second set of EMF readings in the clinical setting.
The triaxial fluxgate magnetometer was determined to be moderately responsive to changes in magnetic field frequency below 10 Hz. At frequencies above 10 Hz the readings corresponded to that of the ambient static geofield. The practitioner operating the Toftness Sensometer was unable to detect magnetic fields at high frequencies (above 10 Hz) even at very high EMFs. The fluxgate magnetometer was shown to be essentially a DC/static magnetic field detector and like all such devices it has a limited frequency range with some low level of sensitivity at very low field frequencies. The interexaminer reliability of four Toftness practitioners using the Sensometer on 5 patients showed low to moderate correlation.
The fluxgate magnetometer although highly sensitive to static (DC) EMFs has only limited sensitivity to EMFs in the range of 1 to 10 Hz and is very insensitive to frequencies above 10 Hz. In laboratory comparisons of the Sensometer and the fluxgate magnetometer there was an occasional correspondence between the two instruments in detecting magnetic fields within the Merritt coil but these occasions were not reproducible. In the clinical studies there was low to moderate agreement between the clinicians using the Sensometer to diagnosing spinal conditions and there was little if any agreement between the Sensometer and the fluxgate magnetometer in detecting EMFs emanating from the volunteers body surface.
自古希腊时代起，利用磁场治疗疾病就引起了人类的兴趣。最近有研究表明，电磁场（EMF）治疗有助于骨愈合，重复经颅磁刺激（rTMS）似乎对治疗精神分裂症和抑郁症有益。由于外部电磁场会影响人体内部过程，我们推测测量体表电磁场可能用于检测疾病状态并指导后续治疗过程。然而，测量微小的体表电磁场需要使用灵敏且记录完善的磁力计。在本研究中，我们评估了一种带有三轴探头的磁通门磁力计用于检测体表电磁场的灵敏度和频率响应，并在实验室和临床环境中将该磁力计的读数与由经验丰富的临床医生操作的托夫尼斯感测仪的信号进行了比较。
使用Peavy音频放大器和可变功率输出的Telulex信号发生器在三线圈梅里特线圈系统中产生50微特斯拉的电磁场。使用校准过的磁力计在该线圈中设置60赫兹、50微特斯拉的磁场，并用电流表测量产生50微特斯拉磁场所需的电流。在60赫兹以外的频率下，通过调整Telulex信号输出以保持电流恒定，使场强维持在50微特斯拉。使用连接到示波器的10匝线圈监测产生的磁场。示波器读数表明在所有测试频率下场强相同。为了确定磁通门磁力计（FGM1）检测到的信号与托夫尼斯感测仪检测到的信号之间是否存在对应关系，将这两种设备都放置在梅里特线圈中，并记录FGM1的读数，并与经验丰富的托夫尼斯操作员检测50微特斯拉磁场的能力进行比较。随后，在临床环境中，由一名FGM1技术人员进行FGM1读数，由4名对该设备有不同程度经验的托夫尼斯感测仪操作员进行感测仪读数。每位检查人员在单独的整脊调整室中从5名不同的志愿者那里获取仪器读数。此外，其中一台托夫尼斯感测仪配备了集成磁通门磁力计（FGM2），该磁力计用于在临床环境中获取第二组电磁场读数。
确定三轴磁通门磁力计对低于10赫兹的磁场频率变化有适度响应。在高于10赫兹的频率下，读数与周围静态地磁场的读数一致。操作托夫尼斯感测仪的从业者即使在非常高的电磁场下也无法检测到高频（高于10赫兹）的磁场。磁通门磁力计本质上是一个直流/静态磁场探测器，与所有此类设备一样，它具有有限的频率范围，在非常低的场频率下灵敏度较低。四名使用感测仪的托夫尼斯从业者对5名患者的检查者间可靠性显示出低到中等的相关性。
磁通门磁力计虽然对静态（直流）电磁场高度敏感，但对1至10赫兹范围内的电磁场灵敏度有限，对高于10赫兹的频率非常不敏感。在实验室中对感测仪和磁通门磁力计进行比较时，在检测梅里特线圈内的磁场时，这两种仪器偶尔会出现对应情况，但这些情况不可重复。在临床研究中，使用感测仪诊断脊柱疾病的临床医生之间存在低到中等程度的一致性，而在检测志愿者体表发出的电磁场方面，感测仪和磁通门磁力计之间几乎没有一致性。
