On-site Rapid Diagnosis of Intracranial Hematoma using Portable Multi-slice Microwave Imaging System

Abstract

Rapid, on-the-spot diagnostic and monitoring systems are vital for the survival of patients with intracranial hematoma, as their conditions drastically deteriorate with time. To address the limited accessibility, high costs and static structure of currently used MRI and CT scanners, a portable non-invasive multi-slice microwave imaging system is presented for accurate 3D localization of hematoma inside human head. This diagnostic system provides fast data acquisition and imaging compared to the existing systems by means of a compact array of low-profile, unidirectional antennas with wideband operation. The 3D printed low-cost and portable system can be installed in an ambulance for rapid on-site diagnosis by paramedics. In this paper, the multi-slice head imaging system's operating principle is numerically analysed and experimentally validated on realistic head phantoms. Quantitative analyses demonstrate that the multi-slice head imaging system is able to generate better quality reconstructed images providing 70% higher average signal to clutter ratio, 25% enhanced maximum signal to clutter ratio and with around 60% hematoma target localization compared to the previous head imaging systems. Nevertheless, numerical and experimental results demonstrate that previous reported 2D imaging systems are vulnerable to localization error, which is overcome in the presented multi-slice 3D imaging system. The non-ionizing system, which uses safe levels of very low microwave power, is also tested on human subjects. Results of realistic phantom and subjects demonstrate the feasibility of the system in future preclinical trials.

Figure 1. The architecture of the multi-slice microwave based head imaging system.

(a) Proposed preclinical multi-slice wideband microwave head imaging system with the schematic representation of the interconnections. (b) The Photograph of the 3D printed head imaging crown mount, showing the adjustable joints, height adjuster for multi-slice scanning and cable holder. (c) The photograph of the scale-engraved antenna holder with the separator and utilized lightweight excitation cable. (d) Photograph of the 3D printed head imaging crown depicting the orientations of the sensing antenna holders and the top height adjusting support.

Figure 2

(a) Schematic diagrams of the designed antenna showing the 3D, top and side views and indicating the detailed dimensions of different parts. (b) Comparison between the measured and simulated reflection coefficient and gain versus frequency performance of the antenna over a wideband. Very low deviation in measurement from the simulated results is observed. (c) Different perspectives of the prototyped antenna illustrating the multiple soldering connections required for fabrication.

Figure 3

(a) Measured radiation patterns of the prototyped antenna at 1.3, 1.8 and 2.3 GHz in both of the E- and H-planes. (b) Simulated 3D radiation patterns of the antenna at 1.2 and 2.2 GHz. (c) The time-domain signals received by the probes placed around the antenna in different angles on both of the E- and H-planes. (d) The fidelity and pulse merit factor patterns of the wideband antenna in E- and H-planes resulted from the transient analysis.

Figure 4

(a) The setup environment of the numerical analysis showing different levels (L1 to L5), while the scanning array is positioned in S3. The antennas are numbered anticlockwise starting antenna-1 in front of the forehead. (b) The illustration of different scanning array positions. The red stars represent the phase centres of the antennas. (c) The side view of the mid-sagittal plane cross section depicting the array of E-field probes utilized for the time-domain analysis. (d–g) The fidelity factor and pulse merit factor results of different time-domain pulses transmitted from antenna-1 and received at different distances inside the realistic human head model. (h) The total time-domain E_z-field distributions of the horizontal cross-sections of different levels for different scanning array positions. The E_z-fields are normalized with respect to the maximum emitted E_z-field value from antenna-1 considering all scanning positions.

Figure 5

(a) The maximum scattered E_z-field over the wide operating band at three different vertical levels with (a) 10 mm and (b) 20 mm separation where the ICH target is placed at the mid-level (L3) for the scanning. In the scanning array only antenna-1 (antenna in front of forehead) is excited. (c) The E_z-field distributions of 2D cross-sections of different levels and for different excitations illustrating the scattered fields generated by the ICH target which is placed at L3 level.

Figure 6. The reconstructed images of realistic human head phantom at five different levels for four different cases.

(a) Healthy, (b) shallow-right, (c) deep-left, (d) deep-back positions. (e) The quantitative analysis results of the detected targets in the detected level. (f) The statistical analysis results of the maximum and average intensities in neutral and suspected regions. MI = maximum intensity, AI = average intensity, S. R. = suspected region and N. R. = neutral region. The green and blue boxes represent the 75^th and 25^th percentiles respectively and the transitional line between them presents the median. The red and violet lines accordingly state the maximum and minimum magnitudes.

Figure 7

(a,b) The image formation results of two volunteers’ heads scanned at three different levels. (c) The maximum and average intensity comparisons between the suspected and neutral regions for five different volunteers. (d) The statistical analysis of the maximum and average intensities of neutral and suspected regions. The green and blue boxes represent the 75^th and 25^th percentiles, respectively, and the transitional line between them presents the median. The red and violet lines accordingly state the maximum and minimum magnitudes.

Figure 8

(a) The comparative view of the statistical analyses among the MIR and AIR values of the healthy head phantom and volunteer head, and unhealthy human head phantoms. MIR = maximum intensity ratio and AI = average intensity ratio. The green and blue boxes represent the 75^th and 25^th percentiles, respectively, and the transitional line between them presents the median. The red and violet lines accordingly state the maximum and minimum magnitudes. (b) The standard deviation results of each individual phantom and volunteer cases in terms of the intensity ratios of neutral and suspected regions.