RadioImager and Radiotomography
Introduction
Radio Imaging
Electromagnetic Tomography, also known as Radio Imaging Method (RIM) gives an image of the rock between two bores or mine drives. Technically it gives the conductivity distribution of the ground between a transmitting antenna and receiving antenna . The method is similar to a medical CT Scan, however our access around the feature of interest is often limited to boreholes or roadways either side of the target. Thus we acquire a 2D image that represents a slice through the target.
Equipment There are two parts to the Rim system
Both systems contain H field antennas operating at frequencies of 2.5 to 992kHz. The RIM2 system measures both amplitude and phase data by means of a control unit. This unit couples and synchronizes the borehole transmitter and receiver. The RIM2020 system measures only amplitude information. ??The RIM2 probes are 4m long and 45mm wide, enabling a wide selection of holes diameters to be surveyed. They are connected to winches via 550m of milspec kevlar reinforced fibre optic cable. The use of fibre optic cable greatly improves the signal to noise ratio and effectively isolates the tools as point source transmitters and receivers. The Queensland and New South Wales Mines Departments certify both the RIM2 and RIM2020 tools Intrinsically Safe.
Radio Imaging Theory
The radio signal loses strength (attenuated) as it propagates through the earth. The signal attenuation is a function of the transmission frequency and the electrical conductivity of the media. By setting up a transmitter at one point and a receiver at another it is possible to measure the signal loss and/or phase change along the path between the two points. By collecting many overlapping raypaths it is possible to invert the attenuation distribution into an image by use of specialised processing software.
A radio signal at a specific frequency travels further through low conductivity media (limestone, coal, potash, meta-sediments, granite) than through materials with high conductivity (shale, mudstone, clay, ore zones etc). Therefore a conductive ore within a resistive host acts as an excellent RIM target.
The data are processed using the state of the art Error! Hyperlink reference not valid. from Error! Hyperlink reference not valid. in Australia. This package is specifically designed for electromagnetic tomography data and contains algorithms such as weight clamping and central weighting to enhance the tomography dataset.
Ground Radar
Wireline Geophysics
Radio Imaging
Quantcast: We developed a technique for making pictures using an ordinary hand-held metal detector - we changed a hand-held metal detector into a camera. This was done by raster-scanning the metal detector using stepper motors under computer control. The resulting imager, called a Scanning Radio Imager (SRI), was used to image various metal objects including coins and hidden weapons. We were able to easily image and distinguish between various coins as well as a number of hidden weapons such as a knife and a gun. Images of these will be presented as well as details of operation. This technique holds great potential for such diverse applications as land-mine detection, and gold prospecting, as well as for airport security. Furthermore, this project provided an interesting undergraduate research project for the presenting author.
Abstract
Determination of the biodistribution of radiopharmaceuticals is an important issue for the evaluation of their performance in diagnosis and therapy. In this study, we evaluated a digital radioimager (RI) based on a multiwire proportional chamber for quantitative autoradiography (AR). The RI allows direct detection of electronic emissions of gamma emitters. Its qualitative and quantitative performances were tested on Tc and In labelled sections and compared with conventional film AR. Linearity of count rate versus activity was verified over a range of activity. As compared with film AR, a substantial improvement of the detection limit was obtained even for acquisition periods up to 20 times less than film exposure times. We provided the basis for quantitative analysis with tissue equivalent paste standards: the Tc and In RI counting efficiencies were respectively 1.19% and 2.35%. We illustrated the respective values of RI and film AR in two rat studies: Tc-DMSA in kidney and dual-isotope Tc-MIBI and In-antimyosin in heart. Calculated activity concentrations on sections of rat organs confirmed good correlation to gamma counting (deviation less than 12%). We suggest RI as a convenient technique for fast localization of single or dual-isotope tracers and determination of activity distribution.
Radio Tomography
Abstract: Radio Tomography (RTFEM) is applied in mine to define geological hazards in advance of coal mining, outline ore bodies in base metal exploration and a range of geotechnical and environmental applications. This paper ranks the dominant sources of image degradation in terms of significance, so as to provide guidelines on the practical applicability of the technique. RTFEM appears to have niche rather than general applicability: it cannot accurately image features oriented parallel to the survey line; it will not generally be able to probe the interior of targets unless the attenuation is such that signal is observable through the strongly attenuated zone (ie above noise level); The resolution perpendicular to the access lines will always be relatively poor. A realistic version of the actual conductivity (or attenuation) image can be achieved by using robust imaging inversion methods. For base metal imaging, it would also be desirable to develop algorithms which can deal better with signal attenuated below the noise level at the receiver, and which can take better account of the variation in antenna coupling. The current approaches still have significant limitations. The technique is applicable for coal seam imaging, but resolution parallel to data collection lines is two to three times less. In these cases usually the only feature observable is a step in image level and not the outline of a structure. The technique is well suited for delineating the external geometry of base metal deposits when the host rock is relatively homogeneous and resistive. This precludes working in areas where the host rock is pervasively altered or pervasively mineralised with disseminated sulphides.