In vitro comparative study of vibro-acoustography versus pulse-echo ultrasound in imaging permanent prostate brachytherapy seeds

Abstract

Background-Permanent prostate brachytherapy (PPB) is a common treatment for early stage prostate cancer. While the modern approach using trans-rectal ultrasound guidance has demonstrated excellent outcome, the efficacy of PPB depends on achieving complete radiation dose coverage of the prostate by obtaining a proper radiation source (seed) distribution. Currently, brachytherapy seed placement is guided by trans-rectal ultrasound imaging and fluoroscopy. A significant percentage of seeds are not detected by trans-rectal ultrasound because certain seed orientations are invisible making accurate intra-operative feedback of radiation dosimetry very difficult, if not impossible. Therefore, intra-operative correction of suboptimal seed distributions cannot easily be done with current methods. Vibro-acoustography (VA) is an imaging modality that is capable of imaging solids at any orientation, and the resulting images are speckle free.Objective and methods-The purpose of this study is to compare the capabilities of VA and pulse-echo ultrasound in imaging PPB seeds at various angles and show the sensitivity of detection to seed orientation. In the VA experiment, two intersecting ultrasound beams driven at f 1 = 3.00 MHz and f 2 = 3.020 MHz respectively were focused on the seeds attached to a latex membrane while the amplitude of the acoustic emission produced at the difference frequency 20 kHz was detected by a low frequency hydrophone.Results-Finite element simulations and results of experiments conducted under well-controlled conditions in a water tank on a series of seeds indicate that the seeds can be detected at any orientation with VA, whereas pulse-echo ultrasound is very sensitive to the seed orientation.Conclusion-It is concluded that vibro-acoustography is superior to pulse-echo ultrasound for detection of PPB seeds.

Prostate Cryotherapy Monitoring Using Vibroacoustography: Preliminary Results of an Ex Vivo Study and Technical Feasibility

“…Examples of such applications include detection of breast mass lesions and microcalcifications [38]–[41], mass lesions in excised human liver [42], and permanent brachytherapy metallic seeds [43] in an excised human prostate [44]. The feature of this technique versus conventional ultrasound is its insensitivity to object orientation [45], its speckle-free mode, and its high sensitivity to variations of tissue stiffness. The aim of this initial study is to introduce VA as an innovative image-guiding tool for cryotherapy monitoring and an alternative technique to TRUS.…”

A Review of Vibro-acoustography and its Applications in Medicine

“…The detectability of brachytherapy seeds has been shown to be enhanced compared to pulse-echo imaging techniques [93]. The integrated optical density (IOD), a measure of image intensity, was computed for both pulse-echo and VA imaging with transducer rotated at different angles with respect to the brachytherapy seeds.…”

Vibro-acoustography beam formation with reconfigurable arrays

“…One way to correct this imbalance is to devote more channels to one beam versus the other. We can define N c as (12) where N c,1 and N c,2 are the number of channels devoted to the beams for f 1 Fig. 2 exemplifies the confocal-like implementation adopted in this simulation.…”