# Patent

## Title
Systems and methods of high frame rate streaming for treatment monitoring

## Abstract

Systems and techniques of treatment monitoring include acquiring channel data from each of a plurality of channels of a signal array over a plurality of frames, determining a reconstruction matrix based on a reconstruction operation to be performed on the channel data, applying the reconstruction matrix to the channel data to obtain reconstructed channel data, estimating displacement data representing displacement of an object over the frames from the reconstructed channel data; determining a conversion matrix based on a conversion operation to be performed on the reconstructed channel data, and applying the conversion matrix to the reconstructed channel data to obtain a displacement map.

## Background
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims the benefit of U.S. Provisional Patent Application Nos. 61/832,503, filed Jun. 7, 2013, and 61/983,733, filed Apr. 24, 2014, each of which is incorporated by reference herein in its entirety.


STATEMENT REGARDING FEDERALLY-SPONSORED RESEARCH
This invention was made with government support from the National Institutes of Health under Grant No.s R01HL114358 and R01EB014496. The government has certain rights in the invention.


BACKGROUND
Certain systems and techniques for treatment monitoring utilize separate acquisition and processing units, for example to perform certain processes, such as displacement estimation, offline in a separare hardware unit. To implement such techniques in a clinical setting, it can be desirable to implement a clinically-oriented, fully-integrated high frame rate platform suitable to analyze and stream real-time feedback of treatment assessment to a user.
High frame-rate imaging can be considered in relation to parallel beamforming, which, alone or in combination with fast analog multiplexing, can reconstruct an entire image following a single acoustic transmission with frame rates up to 1000 frames per second. Parallel processing techniques can be implemented and performed in vivo using a phased array configuration, for example “Explososcan”, where data acquisition rates can be quadrupled with simultaneously reconstructing four receiving beams per a wide single transmit beam. Certain Graphical Processing Unit (GPU)-based beamforming approaches can further increase the imaging framerate and resolution. Such GPU-based approaches can also achieve high frame rate imaging, including, for example, Synthetic Aperture (SA) imaging and Short-lag Spatial Coherence Imaging (SLSC).
In certain imaging techniques, including ultrasound elasticity imaging, software beamforming techniques utilizing various transmit sequences can achieve high imaging rates and resolution, such as composite imaging, plane-wave or divergent transmit beam. High frame rate elasticity imaging can provide suitable quantitative imaging of tissue properties, for example with estimation of motion generated by external compression or acoustic radiation force such as Transient Elastography, Shear Wave Imaging (SSI), Elastography, ARFI imaging, and Harmonic Motion Imaging.
Certain imaging techniques, including ultrasound elasticity imaging, can utilize previously beamformed RF signals, which can be obtained from the beam reconstruction of the entire field of view through the entire imaging depth. Harmonic Motion Imaging for Focused Ultrasound (HMIFU) is a treatment monitoring technique for High-Intensity Focused Ultrasound (HIFU). HMIFU utilizes an Amplitude-Modulated HIFU beam to induce a localized focal oscillatory motion, which can be simultaneously estimated and imaged by HMI. In localized elasticity imaging for HMIFU, generally only the focal spot is considered as the region of interest. As such, suitable beamforming strategies for HIFU treatment monitoring can be configured to reconstruct only the focal region, which can reduce computational cost and allows real-time streaming of elasticity maps throughout the entire treatment window.
However, there remains an opportunity for improved treatment monitoring systems and techniques, for example to provide improved frame rate, improved spatial resolution, and real-time feedback over an extended monitoring period.
SUMMARY
Systems and techniques for treatment monitoring are disclosed herein.
In one embodiment of the disclosed subject matter, methods are provided for treatment monitoring using acquired channel data from each of a plurality of channels of a signal array over a plurality of frames. An example method includes, determining a reconstruction matrix based on a reconstruction operation to be performed on the channel data, applying the reconstruction matrix to the channel data to obtain reconstructed channel data, estimating displacement data representing displacement of an object over the frames from the reconstructed channel data, determining a conversion matrix based on a conversion operation to be performed on the reconstructed channel data, applying the conversion matrix to the reconstructed channel data to obtain a displacement map; and outputting the displacement map to a display.
In some embodiments, the signal array can include an imaging array. The signal array can include an HIFU transducer.
In some embodiments, the reconstruction operation can include an RF reconstruction operation. Additionally or alternatively, the reconstruction operation can include a GPU-based reconstruction operation. The method can include applying a low pass filter to the reconstructed channel data.
In some embodiments, the estimating the displacement data can be performed using a cross correlation technique. The method can further include applying a temporal low pass filter to the estimated displacement data. The conversion operation can include a scan conversion operation. Additionally or alternatively, the conversion operation can include a GPU-based conversion operation. At least one of the reconstruction matrix and the conversion matrix can include a sparse matrix.
In some embodiments, the method can include outputting the displacement map to a display in communication with the processor.
In another embodiment of the disclosed subject matter, systems are provided for treatment monitoring using acquired channel data from each of a plurality of channels of a signal array over a plurality of frames. An example system includes one or more memories and one or more processors coupled to the one or more memories. The one or more processors are configured to determine a reconstruction matrix based on a reconstruction operation to be performed on the channel data, apply the reconstruction matrix to the channel data to obtain reconstructed channel data, estimate displacement data representing displacement of an object over the frames from the reconstructed channel data, determine a conversion matrix based on a conversion operation to be performed on the reconstructed channel data, and apply the conversion matrix to the reconstructed channel data to obtain a displacement map.
In some embodiments, the system can include a display in communication with the processor configured to output the displacement map.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1(a) is an image of an exemplary treatment monitoring system according to the disclosed subject matter.
FIG. 1(b) is a diagram illustrating exemplary signal acquisition system for use with the treatment monitoring system of FIG. 1(a).
FIG. 1(c) is an image illustrating an exemplary imaging array for use with the treatment monitoring system of FIG. 1(a).
FIG. 2(a) is a diagram illustrating an exemplary reconstruction sparse matrix A.
FIG. 2(b) is a diagram illustrating an exemplary channel data matrix
FIG. 2(c) diagram illustrating an exemplary reconstructed RF data matrix
FIG. 3 is a diagram illustrating an exemplary technique for displacement image reconstruction according to the disclosed subject matter.
FIGS. 4(a)-4(h) together illustrate exemplary displacement imaging using the treatment monitoring system of FIG. 1a. Three locations, peak negative (a,b), zero (c,d), and peak positive (e,f) displacement during a 50 Hz-cycle across two independent periods are shown, for purpose of illustration. FIG. 4(g) is a B-mode image of a representative sample. FIG. 4(h) illustrates focal oscillatory displacement produced by the system.
FIGS. 5(a)-5(d) illustrate exemplary B-mode images with peak-to-peak HMI displacement overlay before treatment (a), after treatment (b), the corresponding gross pathology image (c), respectively, along with the focal monitoring displacement across the treatment window (d).
FIGS. 6(a)-6(d) illustrate further exemplary B-mode images with peak-to-peak HMI displacement overlay before treatment (a), after treatment (b), the corresponding gross pathology image (c), respectively, along with the focal monitoring displacement across the treatment window (d).
FIG. 7(a)-7(d) illustrate exemplary in vitro peak-to-peak displacement imaging and monitoring of treatment using the system of FIG. 1a. The peak-to-peak displacement frames during a 50 Hz-cycle at representative time points of (a) 4 seconds, (b) 50 seconds, (c) 87 seconds, and (d) 117 seconds are shown.
FIG. 8 is a diagram illustrating statistical analysis of exemplary treatment monitoring using the system of FIG. 1(a).



Throughout the figures and specification the same reference numerals are used to indicate similar features and/or structures.
DETAILED DESCRIPTION
According to aspects of the disclosed subject matter, systems and methods for treatment monitoring include utilizing a sparse-matrix technique for parallel beamforming and scan conversion to achieve real-time treatment monitoring. It is recognized that the sparse matrix beamforming and reconstruction techniques can be applied to a wide range of imaging and monitoring techniques, including, for example and without limitation, reconstructing data in 3D, trading off the frame rate and motion estimation rates, monitoring treatment in real time and displaying 2D and/or 3D images in real time as well as electronic beam steering and focusing. For purpose of illustration and confirmation of the disclosed subject matter, and without limitation, reference is made to implementing the systems and techniques herein in a fully-integrated, clinically suitable ultrasound scanner with high frame rate real time imaging using HIFU by incorporating a GPU-based algorithm. Such a platform can provide a quantitative real time 2D monitoring feedback during the HIFU treatment directly back to the user.
Harmonic Motion Imaging for Focused Ultrasound (HMIFU) can utilize a single HIFU transducer emitting an amplitude-modulated (AM) beam for inducing both thermal therapy while inducing a stable oscillatory tissue displacement at its focal zone. The oscillatory response, also referred to as HMI displacement, can be estimated using the radio-frequency (RF) signals recorded during the HIFU treatment, as embodied herein, through a confocally-aligned pulse-echo imaging transducer. The localized tissue response can be monitored continuously from the onset of HIFU treatment and can provide the onset of treatment termination to the surgeon based on the change in local tissue stiffness in order to prevent any overtreatment.
With reference to FIGS. 1(a)-1(c), in an exemplary embodiment of a treatment monitoring system, a 93-element, PZT-4 ceramic HIFU Array (H-178, Sonic Concept Inc., Bothell Wash., U.S.A, Diameterindividual element=10 mm, Diameteroverall outer=110 mm, Diameteroverall inner=41 mm, ƒcenter=4.5 MHz, Focal depth=70 mm) can be utilized. The geometric and acoustic parameters of the HIFU transducer can be chosen based on the desired application, embodied herein, for purpose of illustration, as a clinical application of localized HIFU treatment on superficial organ applications. The transducer surface can be covered with a polyurethane based membrane, which can be coupled with a sterilization and degassing system (WDS-104, Sonic Concept, Bothell, Wash., U.S.A.) with control of both volume and circulation flow of degassed cooling water within the transducer-tissue interface during HIFU treatment. All channels for the 93 elements can be synchronously excited by an AM-HIFU signal (ƒcarrier=4.5 MHz, ƒAM=25 Hz) generated through a dual-channel arbitrary waveform generator (AT33522A, Agilent Technologies Inc., Santa Clara, Calif., U.S.A.). The emitted HIFU beam can be capable of inducing an oscillatory motion at the focal zone in addition to inducing the conventional thermal ablation. The oscillatory motion can be estimated based on the RF signals acquired by a confocally aligned diagnostic transducer in order to achieve real-time HMIFU monitoring during HIFU application.
As embodied herein, the extrapolated in situ focal acoustic pressure and intensity (Isptp) can be extrapolated to be 6.5 MPa and 9067 W/cm2, respectively, based on a hydrophone (HGN-0200; Onda Corporation, Sunnyvale, Calif., U.S.A.) calibration procedure. The diagnostic transducer, as embodied herein, can be a 64-element phased array (ATL., Bothell, Wash., U.S.A., ƒcenter=2.5 MHz) and can be confocally fitted through a circular void or the HIFU transducer aperture through a water-proof mechanical gasket with rotational degree of freedoms. In this manner, the confocally-aligned imaging probe can be adjusted rotationally for adaptive targeting and monitoring at 10 steps with individual step of 36°.
Furthermore, and as embodied herein, the phased array transducer can be operated through a 4-board VDAS system (e.g., Verasonics, Bothell, Wash., U.S.A.) and a 260-pin header connector. The coupled transducer pair can be mounted and stabilized on a 3D translational system (e.g., Velmex Inc., Bloomfield, N.Y., U.S.A.) during both imaging and treatment protocols. The transducer pair can be mechanically translated using the translational system between the imaging or therapy protocols for positioning and alignment adjustment purpose, and can be maintained stationary during the imaging and treatment protocols. With reference to FIGS. 1(a) and 1(b), to synchronize the acquisition of the monitoring signals (i.e., the pulse-echo imaging sequence) with the onset of HIFU treatment, the therapeutic transducer can be triggered with the VDAS imaging system, as embodied herein through a MATLAB-based (Mathworks, Natick, Mass., U.S.A.) algorithm on a host PC (embodied herein as Precision T7500, Dell Inc., Austin, Tex., U.S.A.). Upon the initialization of each imaging or therapy monitoring sequence, the VDAS system can send a trigger signal to the waveform generator, which can activate the emission of the focused ultrasound wave emission from the therapeutic transducer. In this manner, for each imaging or therapy monitoring sequence, the initiation of the emission of focused ultrasound wave (e.g., for inducing both motion and therapy effect) and the emission of diagnostic ultrasound wave (e.g., for detecting the induced motion) can be synchronized through the usage of the VDAS unit controlled through a host PC.
The channel data signals can be individually acquired through a 64-element phased array and the Verasonics system, embodied herein using a single-transmit based divergent wavefront imaging sequence. For example and without limitation, and as embodied herein, the acquisition frame rate can be set at 1000 frames/sec, the analog-to-digital (A/D) sampling can be 10 MHz, which can be suitable for use with a 2.5 MHz diagnostic probe. The acquisition sequence can be repeated continuously, and the acquired frames can be transferred in a stacked set of 10 frames through an external function operated within the host computer, where additional reconstruction algorithms can be applied. Beam-formed radio frequency (RF) frames can also be stored, as described further herein, with reference to FIG. 2(c).
GPU-based algorithms can be utilized to improve processing speeds compared to MATLAB implementations. However, translating MATLAB codes, including codes that can rely on pre-compiled proprietary functions to the Compute Unified Device Architecture (CUDA) language, can be a challenge. The systems and techniques described herein can execute linear operations on the GPU with MATLAB integration. As embodied herein, a sparse matrix option of JACKET package (e.g., from AccelerEyes, Atlanta, Ga. U.S.A.) can be utilized to perform sparse matrix-vector products on the GPU in a MATLAB environment. Linear operations can be represented as a matrix (referred to herein as a “function matrix”). As such, as embodied herein, the function matrix can be utilized to obtain a high performance GPU function of the linear operation using the JACKET package. For purpose of illustration, and not limitation, as embodied herein, interpreted MATLAB algorithms to perform the techniques, which can provide increased flexibility and ease-of-use.
For example, a function ƒ can have input x and output y, which can be a combination of any number of linear operations, including compiled functions such as interp2 in MATLAB. In the following equation, the x and y can be represented as vectors (or matrices) containing a total of N and M elements, respectively. As such,

y=ƒ(x)  (1)

ƒ can be linear, and thus a matrix A can be determined such that

y=Ax,  (2)

where y and x can be represented as vectors in RM and RN, respectively, without loss of generality. To find A, ƒ can be applied to the kth standard basis vector ek, embodied herein as a vector with zeros everywhere except in the kth position, and can obtain:





  
    
      
        
          y
          =
          
            f
            ⁡
            
              (
              
                e
                k
              
              )
            
          
        
        ,
      
    
    
      
        (
        3
        )
      
    
  
  
    
      
        
          y
          =
          
            
              ∑
              j
            
            ⁢
            
              
            
            ⁢
            
              
                A
                ij
              
              ⁢
              
                e
                k
              
            
          
        
        ,
        
          1
          ≤
          i
          ≤
          M
        
        ,
      
    
    
      
        (
        4
        )
      
    
  
  
    
      
        
          y
          =
          
            A
            ik
          
        
        ,
        
          1
          ≤
          i
          ≤
          M
        
        ,
      
    
    
      
        (
        5
        )
      
    
  




or, in other words, f(ek) can represent the kth column of the function matrix. This operation can be repeated for all k to obtain the matrix A. The reconstruction matrix can be used for beamforming a set of any amount of frames, and can host data with varying depth and sampling resolution. An exemplary technique for treatment monitoring, embodied herein using a sparse matrix-based beamforming and reconstruction technique is illustrated in FIG. 3. In some applications, for example when utilizing with images, the function matrix A can be very large. For example and without limitation, as embodied herein, the function matrix A can include from 6×109 to 48×109 elements, and can depend at least in part on the up-sampling rate and spatial size of displacement map reconstruction. As such, sparse matrix formats can be utilized to allocate non-zero elements. For example, to perform 2D linear interpolation, vector x can include N elements corresponding to N pixels of a given image, and y can include M>N elements corresponding to M pixels of the interpolated image. For a 4-neighbor interpolation scheme, an interpolated pixel yi can be represented as a linear combination of 4 pixels of vector x. The ith line of Aij can thus be used to compute pixel yi, and as embodied herein, can include 4 non-zero values and N-4 zeros, with N typically larger than 10,000. As such, it can be beneficial, both in terms of memory requirements and computational speeds, to represent the matrix A in its sparse form.

Generating the function matrix can be computationally-complex, both in terms of time and memory; however, the function matrix can be computed once, which can expedite the process of generating the function matrix to code compilation. Additionally, in some embodiments, smaller matrices can be obtained from larger matrices by removing appropriate lines of the function matrix, due at least in part to each column of the function matrix corresponding to one pixel of x, and each line of the function matrix corresponding to one pixel in y. As such, the angle field-of-view and the depth in real-time can be adjusted without re-computing the function matrix.
Furthermore, and as embodied herein, linear operations, such as delay-and-sum beamforming and scan conversion, can be represented as matrix-vector products. To obtain each beamformed RF frame, as embodied herein, two sparse matrices can be generated for reconstruction and scan conversion, respectively. For example, each frame of RF data can be reconstructed by multiplying the channel data matrix with the reconstruction sparse matrix, and multiplying the product matrix by another sparse matrix for scan conversion, as illustrated for example in FIG. 3. As embodied herein, each calculation can be performed as a single operation. Furthermore, and as embodied herein, the RF signals can be up-sampled to 80 MHz and reconstructed on a 90 degrees field of view with 128 beam lines, for example for gelatin phantom imaging studies, and can be reduced to 30 degrees with 32 beam lines, for example for purpose of transfer and storage efficiency in HIFU treatment monitoring studies, as described herein. The reconstruction field of view can be chosen larger than the focal excitation zone as the excitation zone can increase with the formation and growth of the thermal lesion. In addition, a larger field of view can provide additional information, such as the propagation of shear waves in the lateral direction. As embodied herein, constructing the sparse matrix function matrix can be performed on the GPU using MATLAB GPU-compatible operations to reduce processing times.
HMIFU systems can incorporate a low-pass filter or band-pass filter to filter out the HIFU frequency in the received echo from diagnostic transducer, and the configuration can depend on the center frequency of the diagnostic probe with respect to the center frequency of the therapeutic probe. For example, and as embodied herein, a 6th order low pass filter with a cutoff frequency at 4 MHz can be applied to the beamformed RF signals to remove the interference HIFU frequency component without affecting the receiving bandwidth of the diagnostic transducer (2-4 MHz).
Additionally, and as embodied herein, a 1-D normalized cross-correlation technique can be used to estimate the axial displacement along each lateral beam lines between two pre-selected frames within the acquired frames (embodied herein having window size of 3.85 mm and 90% overlap). Another 6th order low pass filter at 100 Hz cutoff frequency can also be applied along the temporal space before construction of the 2D HMI displacement images using the sparse-matrix based scan conversion as described herein, for example with reference to FIG. 3. For purpose of comparison to and confirmation of the disclosed subject matter, another acquisition technique can be utilized to acquire and transfer a separate set of 200 frames and beamformed the frames before being stored in the host computer.
EXAMPLE 1
In one example, for purpose of illustration and confirmation of the disclosed subject matter, a gelatin phantom (n=1, location=3, measurement=3) using gelatin bloom 50 powders (MP Biomedicals LLC., Santa Ana, Calif., U.S.A.) and scatterers using 10% agar powders were provided. As embodied herein, the acoustic attenuation was 0.5 dB/MHz/cm and speed of sound was 1551.7 m/s while the gelatin concentration was 4.9 g/L. The constructed phantom was configured to cure with a cylindrical shape (diameter 120 mm, height 60 mm) with a Young's Modulus of 10 kPa. The phantom was placed on an acoustic absorber to reduce or minimize any interface reflection interference, and degassed echo gel (AQUASONIC®100, Parker Laboratories, Inc., Fairfield, N.J., U.S.A.) was placed above the phantom between the transducer membrane for impedance matching, as shown for example in FIG. 1(a). The imaging sequence included a continuous 1.2 seconds excitation, and data was transferred back to the host PC for a set of 400 ms, equivalent to 20 cycles of HMI excitation. The water in the coupling membrane of the HIFU transducer was degassed for 2 hours prior to treatment monitoring using the circulation system, and acoustic gel was also degassed for one hour prior to treatment monitoring.
Five displacement maps were obtained at three separate locations inside the gelatin phantom. B-mode imaging was performed before each imaging to improve the field of view. For each displacement image, a 1.2 second continuous HMIFU excitation was applied, and the RF signals were recorded at sets of 20-cycles (400 ms). The focal excitation zone was imaged for each location investigated and also centered at the focusing depth of HIFU transducer, embodied herein at 70 mm with −6 dB boundaries encompassing an ellipsoidal shape with diameters of 10 mm (axial) by 5 mm (lateral), as illustrated in FIGS. 4(a)-4(h). The distribution and magnitude range of the displacement profile at maximum excitation (FIG. 4(a), 4(b)), relaxation (FIG. 4(e), 4(f)), and zero (FIG. 4(c), 4(d)) force phase all remained reproducible for each cycle across the entire imaging sequence. Along with the axial displacement from the focal excitation, the estimated displacement within the boundary edge of the phantom includes displacement from the resulted propagation of shear wave associated with each focal excitation. Estimated motion outside the boundary edges of the phantom can be considered to be artifact. The average peak-to-peak HMI displacement at each location was estimated to be 21.9±7.98 μm, 23.9±8.7 μm, and 21.6±2.4 μm, respectively (mean±standard deviation). A full set of displacement frames shown during a 200 ms excitation period allowed vizualization of both focal displacement as well as propagation of shear waves generated from the focal excitation.
EXAMPLE 2
In another example, for purpose of illustration and confirmation of the disclosed subject matter, initial studies (subject=2, lobes=2, treatment location=3) and reproducibility studies (subject=6, lobe=6, treatment location=19) were performed using canine livers excised and immersed into degassed Phosphate buffered saline (PBS) solution bath maintained at temperature of 25° C. The specimens were degassed for two hours prior to treatment monitoring to reduce or prevent any air trapped inside. Each specimen was secured using metallic needles onto an acoustic absorber submerged in a de-ionized and degassed PBS tank, for example as depicted in FIG. 1(a). The HIFU treatment sequence included a continuous 120-seconds excitation, and beamformed RF data frames were transferred back to the host PC at a rate of 100 frames per second, equivalent to 20 cycles of HMI excitation.
For each HIFU treatment, conventional B-mode imaging was used to target the focal zone within the region of interest inside the tissue. In the initial study, three HIFU treatments were performed across two liver lobes with HMIFU monitoring. B-mode images were acquired before and after the HIFU treatment, as illustrated in FIGS. 5 and 6, respectively, and used for overlay with peak-to-peak HMI displacement images. The peak-to-peak HMI displacements within the focal excitation region, as illustrated in FIG. 7, were monitored and processed using the technique discussed in Example 1 throughout the entire 2-minutes HIFU treatment period. A full set of displacement frames were shown during a 120-s HIFU treatment period.
For each of the three initial case studied, a decrease in peak-to-peak HMI displacement of 40%, 30%, and 33% was observed, respectively, as shown in FIGS. 5(f) and 6(f). For the reproducibility cases studied, 18 of the 19 reproducibility study HIFU treatment cases exhibited average displacement decrease of 45.2±20.8%, as illustrated in FIG. 8. The difference between monitoring of displacement at the end of the HIFU treatment was found to be lower than that of the beginning of HIFU treatment (P-value=0.0003). The same decrease trends were also imaged in 2D, where individual single-cycle frame sets including maximum and minimum displacement profiles were shown in FIGS. 5 and 6, representing each of the representative treated locations, respectively. In the initial cases, the detected thermal lesion sizes were also imaged as 251, 254, and 226 mm2 from gross pathology with an expected consistency from the HIFU treatment parameters remaining the same for all cases. In addition, the estimated diameter of HMI focal region from the displacement images across the three treatment cases increased both in axial and lateral direction from before (9.8 mm×8.2 mm, 9.3 mm×7.6 mm, 9.2 mm×6.6 mm, respectively) to after (13.0 mm×11.3 mm, 10.9 mm×8.4 mm, and 10.0 mm×10.5 mm, respectively) HIFU treatment, and thus an estimation of the confirmed thermal lesion diameter from gross pathology (9.0 mm×8.0 mm, 9.0×8.5 mm, 7.5×6.5 mm, respectively) was obtained, as provided in Table 1. The average size of all of the treated thermal lesion sizes in the reproducibility study cases was 236.6±140.2 mm2.







TABLE 1







Comparison table of HMI focal excitation region and the


diameter of thermal lesion size from gross pathology


analysis following in vitro experiment.













Thermal lesion



Focal excitation
Focal excitation
diameter from


Treat-
diameter at T = 5 s
diameter at T = 120 s
gross pathology


ment
(Axial vs. Lateral)
(Axial vs. Lateral)
(Axial vs.


Case
(T = 5 s)
(T = 120 s)
Lateral)





1
9.8 mm × 8.2 mm
13.0 mm vs. 11.3 mm
9.0 mm vs.





8.0 mm


2
9.3 mm × 7.6 mm
10.9 mm vs. 8.4 mm 
9.0 mm vs.





8.5 mm


3
9.2 mm vs. 6.6 mm
10.0 mm vs. 10.5 mm
7.5 mm vs.





6.5 mm









For purpose of configuration of the disclosed subject matter, in Example 1 and 2, the processing speed of each technique was compared to that of a conventional reconstruction algorithm. In Example 1, the motion display (i.e., processing time from data acquisition to displacement estimation) frame rate was 1 Hz using the GPU-based sparse matrix algorithm, 0.4 Hz using the CPU-based sparse matrix algorithm, and 0.01 Hz using the conventional reconstruction algorithm when reconstructing on a 90° field of view (128 lines) image from 50 to 90 mm deep (9.6 μm axial grid size). In Example 2, the motion display (i.e., processing time from data acquisition to displacement estimation) frame rate was 15 Hz and 5 Hz with reconstructing 32 and 64 RF lines, respectively, using the GPU-based sparse matrix, 2.6 and 1 Hz using the CPU-based sparse matrix algorithm, respectively, and 0.09 and 0.05 Hz using the conventional algorithm for a 40 mm range (9.6 μm axial grid size) and 30 degrees angle field of view image. The results of these comparisons are shown in Table 2.







TABLE 2







Online streaming frame rate using CPU-based conventional


reconstruction algorithm, CPU and GPU-based sparse


matrix reconstruction algorithm under HMIFU imaging


settings for a 40 mm range image with 9.6 μm axial grid size.












CPU
GPU



Conventional
based sparse
based sparse



CPU
matrix
matrix


Field of view
reconstruction
reconstruction
reconstruction





30°, 32 Beams
0.09 Hz
2.6 Hz
15 Hz 


30°, 64 Beams
0.05 Hz
  1 Hz
5 Hz


 90°, 128 Beams
0.01 Hz
0.4 Hz
1 Hz









The systems and techniques described herein can provide treatment monitoring which can be localized, performed in real time, and does not further delay the treatment procedure. For purpose of illustration and not limitation, referring now to an application of the treatment monitoring systems and techniques disclosed herein to monitoring HIFU treatment, HMIFU is an acoustic radiation force based dynamic elasticity imaging technique using a HIFU transducer for transmitting an AM-HIFU beam to induce a stable focal oscillatory motion, which can be related to the local tissue mechanical property, tracked by 1D cross correlation of RF signal acquired using a confocally-aligned diagnostic transducer. In this application, HMIFU can be utilized to perform localized HIFU monitoring without interrupting the treatment. Real-time HMIFU with capability to stream displacement during the treatment window can thus be performed using a fast beamforming and reconstruction algorithm, as discussed herein. GPU-based beamforming techniques can be utilized for applications of Synthetic Aperture (SA) imaging, real-time small displacement estimation, and Short-lag Spatial Coherence Imaging (SLSC). For purpose of illustration, and as embodied herein, a 2D HMIFU system equipped with a real-time feedback capable of streaming the displacement image during the ablation procedure utilizes a sparse matrix beamforming algorithm implemented on GPU. Additional exemplary applications of HMI are described, for example and without limitation, in International Patent Application No. PCT/US2014/011631, which is incorporated by reference herein in its entirety.
Challenges to real-time treatment monitoring, for example of HIFU treatment, include detecting the onset of lesion formation, providing quantitative mapping of the treated region (i.e., thermal lesion), and performing efficient monitoring without delaying the treatment procedure. Real-time monitoring and quantitatively mapping thermal lesion formation can be performed at a frame rate of 5 to 15 Hz. This approach can facilitates an enhancing temporal resolution to monitor and detect the onset of thermal lesioning indicating effective point of termination. HMIFU can stream the focal displacement map quantitatively delineating the region of thermal lesion based on the stiffness contrast. ARFI and SSI methodologies can implement a cost-effective, all-ultrasound-based HIFU with a monitoring system receiving beamformed RF signals between 11 to 17 kHz. ARFI can utilize a single transducer excited at a low duty cycle (6%) to reduce or prevent transducer damage with the ARFI image displayed interspersed between HIFU treatments at 0.2-Hz frame rate following a single mechanical excitation. SSI also interrupts the treatment for the HIFU beam during the its plane shear wave excitation, allowing a frame rate up to 0.333 Hz. By comparison, HMIFU can continuously streaming focal displacement maps at up to 15 Hz throughout the entire HIFU treatment duration. The HMIFU system utilizes the same HIFU beam for both treatment and elasticity monitoring, and thus can operate in a more efficient monitoring manner by not stopping HIFU treatment to perform the monitoring/imaging sequence. Even in a CPU implementation without the GPU, the sparse matrix based beamforming technique according to the disclosed subject matter can improved the frame rate by 20 to 40 times from that of a conventional delay-and-sum beamforming algorithm between field of view of 30° to 90°.
With reference to Example 1 described herein, the HMI displacement images across the gelatin phantom were reproducible, with the largest variance across locations being under 9.6%. In addition, the focal excitation region was clearly imaged across all cases, where ellipsoidal shaped displaced regions were centered around 70 mm, in agreement with the expected geometrical focal depth of the HIFU transducer. The displacement profile maps measured across different locations showed a strong consistency, thus confirming the reproducibility of beamforming and motion estimation described herein and confirming performance reliability of the disclosed subject matter. While the HMIFU excitation was continuous for 1.2 seconds, tissue heating and the associated changes such as in speed of sound were negligible within the time window and the associated low temperature changes.
For monitoring of HIFU treatment studies, the focal excitation region was also clearly imaged across all the cases, where focal displacement decreased by 40%, 30%, and 33% for each initial feasibility study cases as well as decreased by 45.2±20.8% amongst the reproducibility study cases upon lesion formation with statistical significance (P=0.0003). The displacement decrease began around 60 to 80 seconds upon treatment initiation and progressively continued until the end. The average size of the treated thermal lesions estimated from gross pathology was 236.6±140.2 mm2 under the same treatment parameters, which also confirmed the consistency of the disclosed subject matter.
The examples illustrate real-time, continuous monitoring and lesion imaging of HIFU treatment, which can allow physicians to identify the onset of lesion formation and provide the ability to either terminate the treatment or continue to monitor lesion growth. Steady decrease in the HMI focal displacement, which can indicate the onset of thermal lesion formation due to stiffening of the treated region, was observed throughout HIFU monitoring window in all of the completed treatment cases. In addition, the overlay of a peak-to-peak HMI displacement map onto the B-mode image can depict the quantitative mapping of mechanical property change of the tissue in addition to the anatomical information provided by the B-mode, as illustrated in FIGS. 5 and 6. Compared to the B-mode assessment, shown in FIGS. 5 and 6, of the same regions before and after HIFU ablation, the peak-to-peak HMI displacement images provided improved contrast and mapping of the thermal lesion. The growth of the focal displacement region can be associated with the growing and stiffer thermal lesion. In addition, the displacement images can reproducibly map the changes in mechanical property upon lesion formation.
The single variable sparse matrices described herein can be constructed offline using a separate algorithm prior to treatment monitoring, and the matrix computational cost can vary between few minutes to several hours, and can depend at least in part on the up-sampling rate, beam density, as well as well as field of view. However, the computational cost can be reduced by generating a single matrix at a highest sampling rate and larger fields of view, and adapting the reconstruction matrices with reshaping and down-sampling in respective to the specific imaging parameter. The reconstruction speed can also influence the streaming speed, where a larger field of investigation with higher sampling rate can have a lower streaming frame rate. The data transfer rate from the VDAS to the host computer can also affect speed. For example, as embodied herein, all 200 frames acquired at 1 kHz frame rate were transferred in 930 ms. In some embodiments, frame rates of at least 10-15 Hz can be considered suitable for HIFU guidance.
The systems and techniques according to the disclosed subject matter can be utilized for rapid-prototyping and implementing on any conventional imaging system, including conventional ultrasound systems. The matrix-based algorithms can allow for flexible adaptation of other types of linear functions. The frame rate of 1 kHz, as embodied herein, can be selected to provide suitable displacement quality (i.e., correlation coefficient) and streaming framerate. In addition, at 1 kHz, both monitoring of focal displacement and capturing the propagation of shear waves generated through focal excitation can be performed. The ability to track shear waves can provide additional applications potentials for the disclosed subject matter, including but not limited to simultaneous focal and peripheral-focal region shear-wave based elasticity imaging of lesion formation, as well as assessment of 2D viscoelasticity change during HIFU treatment. Additional applications can include implementation of a raster-ablation sequence for treatment of large tissue volume through electronic beam steering of the 93-element HIFU array, as well as a composite imaging with real time overlaying displacement image onto B-mode to perform simultaneous beam guidance and lesion assessment. Clinical translation of the disclosed subject matter can be applied to breast and pancreatic tumor ablation.
The foregoing merely illustrates the principles of the disclosed subject matter. Various modifications and alterations to the described embodiments will be apparent to those skilled in the art in view of the teachings herein. It will thus be appreciated that those skilled in the art will be able to devise numerous techniques which, although not explicitly described herein, embody the principles of the disclosed subject matter and are thus within its spirit and scope.

## Claims

1. A method for treatment monitoring using acquired channel data from each of a plurality of channels of a signal array over a plurality of frames, comprising:
determining, using a processor in communication with the signal array, a reconstruction matrix based on a reconstruction operation to be performed on the channel data;
applying, using the processor, the reconstruction matrix to the channel data to obtain reconstructed channel data;
estimating, using the processor, displacement data from the reconstructed channel data, the displacement data representing displacement of an object over the plurality of frames;
determining, using the processor, a conversion matrix based on a conversion operation to be performed on the reconstructed channel data; and
applying, using the processor, the conversion matrix to the reconstructed channel data to obtain a displacement map.

2. The method of claim 1, wherein the signal array comprises an imaging array.

3. The method of claim 1, wherein the reconstruction operation comprises an RF reconstruction operation.

4. The method of claim 1, wherein the reconstruction operation comprises a GPU-based reconstruction operation.

5. The method of claim 1, further comprising applying a low pass filter to the reconstructed channel data.

6. The method of claim 1, wherein the estimating the displacement data is performed using a cross correlation technique.

7. The method of claim 1, further comprising applying a temporal low pass filter to the estimated displacement data.

8. The method of claim 1, wherein the conversion operation comprises a scan conversion operation.

9. The method of claim 1, wherein the conversion operation comprises a GPU-based conversion operation.

10. The method of claim 1, wherein at least one of the reconstruction matrix and the conversion matrix is a sparse matrix.

11. The method of claim 1, further comprising outputting the displacement map to a display device in communication with the processor.

12. A system for treatment monitoring using acquired channel data from each of a plurality of channels of a signal array over a plurality of frames, comprising:
one or more memories; and
one or more processors coupled to the one or more memories, wherein the one or more processors are configured to:
determine a reconstruction matrix based on a reconstruction operation to be performed on the channel data;
apply the reconstruction matrix to the channel data to obtain reconstructed channel data;
estimate displacement data representing displacement of an object over the frames from the reconstructed channel data;
determine a conversion matrix based on a conversion operation to be performed on the reconstructed channel data; and
apply the conversion matrix to the reconstructed channel data to obtain a displacement map.

13. The system of claim 12, wherein the signal array comprises an imaging array.

14. The system of claim 12, wherein the signal array comprises an HIFU transducer.

15. The system of claim 12, wherein the reconstruction operation comprises an RF reconstruction operation.

16. The system of claim 12, wherein the reconstruction operation comprises a GPU-based reconstruction operation.

17. The system of claim 12, wherein the processor is further configured to apply a low pass filter to the reconstructed channel data.

18. The system of claim 12, wherein the displacement data is estimated using a cross correlation technique.

19. The system of claim 12, wherein the processor is further configured to apply a temporal low pass filter to the estimated displacement data.

20. The system of claim 12, wherein the conversion operation comprises a scan conversion operation.

21. The system of claim 12, wherein the conversion operation comprises a GPU-based conversion operation.

22. The system of claim 12, wherein at least one of the reconstruction matrix and the conversion matrix is a sparse matrix.

23. The system of claim 12, further comprising a display, in communication with the processor, to display the displacement map to a user.