X‐ray acoustic computed tomography with pulsed x‐ray beam from a medical linear accelerator

Abstract

Purpose:The feasibility of medical imaging using a medical linear accelerator to generate acoustic waves is investigated. This modality, x-ray acoustic computed tomography (XACT), has the potential to enable deeper tissue penetration in tissue than photoacoustic tomography via laser excitation. Methods: Short pulsed (μs-range) 10 MV x-ray beams with dose-rate of approximately 30 Gy/min were generated from a medical linear accelerator. The acoustic signals were collected with an ultrasound transducer (500 KHz central frequency) positioned around an object. The transducer, driven by a computer-controlled step motor to scan around the object, detected the resulting acoustic signals in the imaging plane at each scanning position. A pulse preamplifier, with a bandwidth of 20 KHz-2 MHz at −3 dB, and switchable gains of 40 and 60 dB, received the signals from the transducer and delivered the amplified signals to a secondary amplifier. The secondary amplifier had bandwidth of 20 KHz-30 MHz at −3 dB, and a gain range of 10-60 dB. Signals were recorded and averaged 128 times by an oscilloscope. A sampling rate of 100 MHz was used to record 2500 data points at each view angle. One set of data incorporated 200 positions as the receiver moved 360• . The x-ray generated acoustic image was then reconstructed with the filtered back projection algorithm. Results: The x-ray generated acoustic signals were detected from a lead rod embedded in a chicken breast tissue. The authors found that the acoustic signal was proportional to the x-ray dose deposition, with a correlation of 0.998. The two-dimensional XACT images of the lead rod embedded in chicken breast tissue were found to be in good agreement with the shape of the object. Conclusions:The first x-ray acoustic computed tomography image is presented. The new modality may be useful for a number of applications, such as providing the location of a fiducial, or monitoring x-ray dose distribution during radiation therapy. Although much work is needed to improve the image quality of XACT and to explore its performance in other irradiation energies, the benefits of this modality, as highlighted in this work, encourage further study.

Simulation and experimental detection of radiation-induced acoustic waves from a radiotherapy linear accelerator

“…This technique is known as x-ray acoustic computed tomography (XACT) and is analogous to photoacoustic tomography (PAT), with the primary difference being that XACT uses a megavoltage x-ray source while PAT uses visible photons from a laser source to induce acoustic waves. The ability to detect IAWs following irradiation by a clinical radiotherapy photon beam was first shown by Bowen et al [4], while XACT and the tomographic approach to image reconstruction was recently demonstrated by Xiang et al [5].…”

X-ray luminescence optical tomography imaging: experimental studies

“…Examples include photoacoustic tomography [1,2] and x-ray acoustic computed tomography [3], in which a pulsed laser or x-ray source, respectively, are used to generate ultrasound inside tissue. Another example is the emerging technique of x-ray luminescence computed tomography (XLCT) that combines the high sensitivity of optical detection with the high spatial resolution of x-ray imaging [4,5].…”

Sub-mSV breast XACT scanner: concept and design

“…The phenomenon of X-ray-induced acoustic waves has been reported [5] and its potential for radiation dose measurement has been explored recently [6], while tomographic imaging with X-ray induced computed tomography (XACT) has been investigated in our previous experiment [7,8]. To induce the X-ray acoustic effect, X-rays are absorbed by the excitation of inner-shell electrons and induce photoelectrons [9,10].…”