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Prostate cancer is the most common malignancy in males and the second leading cause of death due to cancer in the United States. Ultrasound combined with Transrectal ultrasound guided biopsy (TRUS) is the only diagnostic modality in use; however it has low sensitivity and specificity. Need for an improved imaging modality is deeply felt by the comm...
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... — Prostate cancer is the most common malignancy in males and the second leading cause of death due to cancer in the United States. Ultrasound combined with Transrectal ultrasound guided biopsy (TRUS) is the only diagnostic modality in use; however it has low sensitivity and specificity. Need for an improved imaging modality is deeply felt by the community. We propose a novel method and a device for imaging of the prostate, C-scan Photoacoustic (PA) imaging of the prostate. The basic principle, our imaging system design, fabrication and preliminary results are described in this paper. I. I NTRODUCTION Prostate cancer is the most prevalent malignancy in men, second only to lung cancer in causing cancer related deaths. It is projected that 192,280 new cases of prostate cancer will have been diagnosed in the United States in 2009, with an estimated 27,360 deaths [1]. The risk of developing prostate cancer increases as men age. Clinically localized disease is usually suspected based on an elevated prostate-specific- antigen (PSA) or abnormal digital rectal exam (DRE), prompting transrectal ultrasound guided biopsy of the prostate for definitive diagnosis. TRUS however, is not reliable, often missing cancer in more than 30% of the cases because there are cancers that are not visible on TRUS images. At present a reliable imaging modality on which the physicians can base their diagnosis and treatment decisions is lacking [2]. This is the challenge we are trying to address by building and testing a completely new imaging modality for prostate imaging. Photoacoustic refers to a phenomenon where acoustic waves are produced by absorbing points or objects of a medium, such as soft tissue, that is exposed to a beam of low- energy nanosecond (ns) pulse of laser light in the near-infrared (NIR) region, usually defined for wavelengths from 600 nanometers (nm) to 1100 nm. The absorption of a few nanosecond optical pulse causes localized heating and rapid thermal expansion, which generates thermo elastic stress waves (ultrasound waves). We will refer to these waves as the “PA signal”. These waves are generated instantaneously and simultaneously everywhere in the three-dimensional (3D) tissue volume exposed by the laser beam as shown in Fig. ...
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Citations
... In 2008, Rao et al. [16] characterized the acoustic lens based PA imaging system and acquired C-scan images using this system. They developed a lens-based PA imaging probe (PA Camera) to acquire C-scan images of prostate [66] in 2010 and in 2014, they reutilized this PA camera in ex vivo studies [67]. Multispectral PA imaging using the PA camera on prostate, thyroid, and kidney ex vivo human tissue samples was performed by this group [19,[68][69][70] to differentiate between malignant, benign, and normal samples. ...
This paper presents a comparative analysis of the performance of an acoustic lens based reconstruction technique with the conventional back projection algorithm based reconstruction technique used for photoacoustic (PA) imaging. The acoustic lens based reconstruction technique considered in this study used an acoustic lens to create an image of the PA source on the ultrasound (US) transducer array and thus it could produce 2D reconstructed images which represent entire cross sectional planes of the object in real time. This technique could potentially reduce the number of acquisitions significantly from which was required in the case of reconstruction using a conventional algorithm based reconstruction technique. This is a hardware reconstruction technique eliminating the need for heavy computational and memory requirements in algorithm based PA image reconstructions. A linear and a planar US transducer array were used in this study to acquire data from a spherical or a cylindrical point source. Three metrics full width half maximum (FWHM), Pearson Correlation (PC), and energy (E) were used to evaluate the performance of each reconstruction technique. The results of this study showed that the acoustic lens based reconstruction technique is capable to reconstruct 2D PA images with qualities comparable to that of the algorithm based reconstruction techniques.
... Acoustic lens based PA imaging is a potential alternative to conventional computational reconstruction based imaging. The lens-based approach eliminates computational and memory intense reconstruction and offers a simple, lowcost and real-time implementation [2,3]. ...
... A unit magnification lens-based PA system and a peak holding method for image formation can be found in [5][6][7]. Adapting the unit magnification system design in 2010, Valluru et al. proposed a 3D printed imaging probe which enabled a compact system known as a PA camera [2]. The utility of a PA camera in ex vivo studies was presented by Dogra et al. in 2014 [8]. ...
... First is a lens based 3D US signal focusing device, which we refer to here as the PA camera and second is the computationally efficient post-processing methodology that works on the data acquired by the PA camera. The details of the PA imaging camera are given in [2,3,15,16]. The focus of this article is on the second part of the prototype, that is developing a computationally efficient method that improves the 3D image quality by rendering the system PSF uniform throughout the investigated tissue volume. ...
Recently, an acoustic lens has been proposed for volumetric focusing as an alternative to conventional reconstruction algorithms in Photoacoustic (PA) Imaging. Acoustic lens can significantly reduce computational complexity and facilitate the implementation of real-time and cost-effective systems. However, due to the fixed focal length of the lens, the Point Spread Function (PSF) of the imaging system varies spatially. Furthermore, the PSF is asymmetric, with the lateral resolution being lower than the axial resolution. For many medical applications, such as in vivo thyroid, breast and small animal imaging, multiple views of the target tissue at varying angles are possible. This can be exploited to reduce the asymmetry and spatial variation of system the PSF with simple spatial compounding. In this article, we present a formulation and experimental evaluation of this technique. PSF improvement in terms of resolution and Signal to Noise Ratio (SNR) with the proposed spatial compounding is evaluated through simulation. Overall image quality improvement is demonstrated with experiments on phantom and ex vivo tissue. When multiple views are not possible, an alternative residual refocusing algorithm is proposed. The performances of these two methods, both separately and in conjunction, are compared and their practical implications are discussed.
... A system with unit magnification and 4F geometry designed to image a single object plane can be found in Chen et al (2007) and Rao et al (2008). A hand-held probe using this lens-based design was introduced by Valluru et al and the term 'PA camera' was coined (Valluru et al 2010). This system can be used for several applications, including in vivo imaging. ...
... The tissue was 24 mm × 40 mm × 3 mm in size. A C-scan was conducted using a stepper motor, and the measured A-line signals were stacked to form 3D data (Valluru et al 2010). The tissue was kept at an off-focal point of 2F + 5 mm from the lens center. ...
In photoacoustic (PA) imaging, an acoustic lens-based system can form a focused image of an object plane. A real-time C-scan PA image can be formed by simply time gating the transducer response. While most of the focusing action is done by the lens, residual refocusing is needed to image multiple depths with high resolution simultaneously. However, a refocusing algorithm for PA camera has not been studied so far in the literature. In this work, we reformulate this residual refocusing problem for a PA camera into a two-sided wave propagation from a planar sensor array. One part of the problem deals with forward wave propagation while the other deals with time reversal. We have chosen a Fast Fourier Transform (FFT) based wave propagation model for the refocusing to maintain the real-time nature of the system. We have conducted Point Spread Function (PSF) measurement experiments at multiple depths and refocused the signal using the proposed method. Full Width at Half Maximum (FWHM), peak value and Signal to Noise Ratio (SNR) of the refocused PSF is analyzed to quantify the effect of refocusing. We believe that using a two-dimensional transducer array combined with the proposed refocusing, can lead to real-time volumetric imaging using a lens based PA imaging system.
... A low-cost method using 3D printing technology to manufacture acoustic lenses and a preliminary characterization was conducted by Rao et al. in 2008 [17]. Along with the use of 4F imaging system, the group developed a scanning probe, known as PA camera [18]. This technique has proved to be a cost-effective alternative to the conventional PA imaging system with several advancements on the clinical side, including ex vivo studies [19] and system designs for in vivo imaging [20]. ...
Some of the challenges in translating photoacoustic (PA) imaging to clinical applications includes limited view of the target tissue, low signal to noise ratio and the high cost of developing real-time systems. Acoustic lens based PA imaging systems, also known as PA cameras are a potential alternative to conventional imaging systems in these scenarios. The 3D focusing action of lens enables real-time C-scan imaging with a 2D transducer array. In this paper, we model the underlying physics in a PA camera in the mathematical framework of an imaging system and derive a closed form expression for the point spread function (PSF). Experimental verification follows including the details on how to design and fabricate the lens inexpensively. The system PSF is evaluated over a 3D volume that can be imaged by this PA camera. Its utility is demonstrated by imaging phantom and an ex vivo human prostate tissue sample.
... Figure 6 illustrates our acoustic lens based technology for PAI implemented using 3D printing technology [18] . Following the laser excitation of the target, PA signals are generated from all the absorbers of the target and are simultaneously focused onto an US detector by the acoustic lens [19] . The acoustic lens corrects for the loss of lateral image resolution as explained in [20]. ...
We have designed and implemented a novel acoustic lens based focusing technology into a prototype photoacoustic imaging camera. All photoacoustically generated waves from laser exposed absorbers within a small volume get focused simultaneously by the lens onto an image plane. We use a multi-element ultrasound transducer array to capture the focused photoacoustic signals. Acoustic lens eliminates the need for expensive data acquisition hardware systems, is faster compared to electronic focusing and enables real-time image reconstruction. Using this photoacoustic imaging camera, we have imaged more than 150 several centimeter size ex-vivo human prostate, kidney and thyroid specimens with a millimeter resolution for cancer detection. In this paper, we share our lens design strategy and how we evaluate the resulting quality metrics (on and off axis point spread function, depth of field and modulation transfer function) through simulation. An advanced toolbox in MATLAB was adapted and used for simulating a two-dimensional gridded model that incorporates realistic photoacoustic signal generation and acoustic wave propagation through the lens with medium properties defined on each grid point. Two dimensional point spread functions have been generated and compared with experiments to demonstrate the utility of our design strategy. Finally we present results from work in progress on the use of two lens system aimed at further improving some of the quality metrics of our system.
... The broad clinical utility of photoacoustic imaging to improve prostate cancer detection, treatment, and assessment relies on a minimally invasive light delivery method that offers sufficient fluence to illuminate targets of interest within laser safety limits. Valluru et al. 29 proposed a transrectal light delivery method to achieve this goal. Although it is minimally invasive, as the optics could be integrated with current transrectal US probes, this approach is limited by poor light penetration through the rectal wall. ...
Photoacoustic imaging has broad clinical potential to enhance prostate cancer detection and treatment, yet it is challenged by the lack of minimally invasive, deeply penetrating light delivery methods that provide sufficient visualization of targets (e.g., tumors, contrast agents, brachytherapy seeds). We constructed a sidefiring fiber prototype for transurethral photoacoustic imaging of prostates with a dual-array (linear and curvilinear) transrectal ultrasound probe. A method to calculate the surface area and, thereby, estimate the laser fluence at this fiber tip was derived, validated, applied to various design parameters, and used as an input to three-dimensional Monte Carlo simulations. Brachytherapy seeds implanted in phantom, ex vivo, and in vivo canine prostates at radial distances of 5 to 30mm from the urethra were imaged with the fiber prototype transmitting 1064 nm wavelength light with 2 to 8 mJ pulse energy. Prebeamformed images were displayed in real time at a rate of 3 to 5 frames per second to guide fiber placement and beamformed offline. A conventional delay-and-sum beamformer provided decreasing seed contrast (23 to 9 dB) with increasing urethra-to-target distance, while the shortlag spatial coherence beamformer provided improved and relatively constant seed contrast (28 to 32 dB) regardless of distance, thus improving multitarget visualization in single and combined curvilinear images acquired with the fiber rotating and the probe fixed. The proposed light delivery and beamforming methods promise to improve key prostate cancer detection and treatment strategies.
... The broad clinical utility of photoacoustic imaging to improve prostate cancer detection, treatment, and assessment relies on a minimally invasive light delivery method that offers sufficient fluence to illuminate targets of interest within laser safety limits. Valluru et al. 29 proposed a transrectal light delivery method to achieve this goal. Although it is minimally invasive, as the optics could be integrated with current transrectal US probes, this approach is limited by poor light penetration through the rectal wall. ...
We present a novel approach to photoacoustic imaging of prostate brachytherapy seeds utilizing an existing urinary catheter for transurethral light delivery. Two canine prostates were surgically implanted with brachyther- apy seeds under transrectal ultrasound guidance. One prostate was excised shortly after euthanasia and fixed in gelatin. The second prostate was imaged in the native tissue environment shortly after euthanasia. A urinary catheter was inserted in the urethra of each prostate. A 1-mm core diameter optical fiber coupled to a 1064 nm Nd:YAG laser was inserted into the urinary catheter. Light from the fiber was either directed mostly parallel to the fiber axis (i.e. end-fire fire) or mostly 90° to the fiber axis (i.e. side-fire fiber). An Ultrasonix SonixTouch scanner, transrectal ultrasound probe with curvilinear (BPC8-4) and linear (BPL9-5) arrays, and DAQ unit were utilized for synchronized laser light emission and photoacoustic signal acquisition. The implanted brachytherapy seeds were visualized at radial distances of 6-16 mm from the catheter. Multiple brachytherapy seeds were si- multaneously visualized with each array of the transrectal probe using both delay-and-sum (DAS) and short-lag spatial coherence (SLSC) beamforming. This work is the first to demonstrate the feasibility of photoacoustic imaging of prostate brachytherapy seeds using a transurethral light delivery method.
The purpose of this study was to optimize the light delivery method in a prostate photoacoustic imaging system. A three dimensional (3D) optical model of the human prostate was developed, and the optical energy distribution in the prostate was estimated via three-dimensional Monte Carlo simulation. Then, the feasibility of prostate photoacoustic imaging (PAI) using two endoscopic light delivery methods was studied. Photoacoustic pressure generation and the corresponding photoacoustic images had been obtained and the comparisons were made between each other. Also, the results of cylinder diffusing light source with different lengths were compared. After that, phantom experiment was carried out to validate the simulation results. Our results would be significant in the optimizing photoacoustic imaging system for an accurate diagnosis of prostate cancer.
In implementing prostate cancer screening using photoacoustic imaging (PAI), transrectal delivery of light and transrectal ultrasound (TRUS) transducer for signal detection is the most commonly used approach for PAI system design. In this approach, energy-efficient light delivery and good alignment of laser excitation and acoustic detection are very important for optimal imaging sensitivity. The previously published works adopted dark-field illumination for their probes. In this study, we proposed and achieved bright-field illumination, which enables more laser energy to be delivered to the region of interest for imaging, resulting in higher sensitivity of the probe. Further, by using a single optical fiber instead of fiber bundle, the efficiency of laser transmission was significantly enhanced. The adoption of single optical fiber also enhances the flexibility of the probe for operation and lower the cost. A custom designed photoacoustic imaging system was built in this study to verify the feasibility of the probe for clinical translational application. The spatial resolution and enhanced signal-to-noise ratio (SNR) of the proposed probe were validated using PAI of phantoms. We demonstrated the use of probe in diagnosing prostate cancer in vivo using a canine model mimicking prostate cancer. Our results showed that the proposed probe could achieve high sensitivity and a wide field-of-view (FOV) in imaging prostate cancer. We also performed minimally-invasive real-time guidance of needle biopsy in ex vivo prostate, showing the potential of the probe for early screening of prostate cancer and early preventive treatment of prostate tumor.
