3-D Hemorrhage Imaging by Cambered Magnetic Induction Tomography

Magnetic induction tomography (MIT) is a promising imaging technique for hemorrhage detection due to the features of initial diagnosis and continuous monitoring. The dispersed nature of the electromagnetic field makes the MIT difficult to image the intraaxial hemorrhage. An open cambered MIT was proposed to improve the sensitivity of extraaxial hemorrhage which is located 14-20 mm below the scalp. Realistic head models with different hemorrhage volumes and positions are used for simulation. The imaging performance of the cambered MIT is compared with the cylindrical MIT based on the time-difference and frequency-difference imaging methods, respectively. Different levels of noise (standard deviation of phase difference at 0.5 and 0.75 m°) were added to the phase difference measurements of time difference at 1 MHz. 3-D images were reconstructed by the single-step Tikhonov regularization method. Two factors of correlation coefficient rpd and localization error Le are introduced to assess the quality of the images. The results show that the cambered MIT obtains a better imaging performance of extraaxial hemorrhage than cylindrical MIT. In particular, for the hemorrhage of 7 mL at the lower position by time-difference imaging, rpd of the cambered MIT is increased by 42.3% and Le is reduced by 37.7% relative to the cylindrical MIT. The cambered MIT obtained twice the signal-to-noise ratio of phase difference for the frequency-difference method than the cylindrical MIT. The cambered MIT improves the sensitivity of near-subsurface locations, which provides a high resolution and portable way to monitor the extraaxial hemorrhage.

I. Introduction

Intracranial hemorrhage is an accumulation of blood inside the skull, which can be caused by physical trauma, diabetes, hypertension, and so on. It belongs to intracranial space occupying lesion and will increase the pressure in the brain, which can cause brain damage and can be life-threatening. The intracranial hemorrhage contains intraaxial hemorrhage and extraaxial hemorrhage. The intraaxial hemorrhage is bleeding within the brain tissue or the brain’s ventricles. The extraaxial hemorrhage happens in the dura, arachnoid, subarachnoid, and pia maters, which includes epidural hemorrhage, subdural hemorrhage, and subarachnoid hemorrhage. Fig. 1 shows the locations of intraaxial and extraaxial hemorrhages. Medical diagnostic imaging techniques such as computed tomography (CT) and magnetic resonance imaging (MRI) greatly help the doctors to diagnose the hemorrhage for further surgical treatment, but they also have some limitations. CT is based on the ability of different organs or tissues to absorb the X-ray beam [1]. The high radiation dose is harmful, which limits the use of CT, especially in the gynecology and obstetrics and pediatrics. MRI images reflect the radio signals sent out by different protons when the strong magnetic fields are changed from turning on to off [2]. People with the ferromagnetic implant or cardiac pacemaker are not allowed to use MRI. Magnetic induction tomography (MIT) is a promising imaging technique that can reconstruct the conductivity distribution of objects based on the Faraday law of electromagnetic induction [3], [4]. It is widely investigated not only in industrial applications (e.g., molten metal flow visualization [5], [6]) but also in biomedical applications. MIT has the advantages of noncontact, low cost, fast imaging, and harmless. More importantly, MIT can provide an initial diagnosis of hemorrhage in case of emergency, monitor the development of hemorrhage at the bedside, and analyze the bioelectrical impedance spectroscopy of tissues, which is significant for humans [7]. Fig. 1.

Location of intraaxial and extraaxial hemorrhages (generated based on the Multimodal Imaging-Based Detailed Anatomical model in [8]).