Development and validation of a radiofrequency ablation treatment planning system for vertebral metastases.

PURPOSE: Bone-targeted radiofrequency ablation (RFA) is widely used in the treatment of vertebral metastases. While radiation therapy utilizes established treatment planning systems (TPS) based on multimodal imaging to optimize treatment volumes, current RFA of vertebral metastases has been limited to qualitative image-based assessment of tumour location to direct probe selection and access. This study aimed to design, develop and evaluate a computational patient-specific RFA TPS for vertebral metastases. METHODS: A TPS was developed on the open-source 3D slicer platform, including procedural setup, dose calculation (based on finite element modelling), and analysis/visualization modules. Usability testing was carried out by 7 clinicians involved in the treatment of vertebral metastases on retrospective clinical imaging data using a simplified dose calculation engine. In vivo evaluation was performed in a preclinical porcine model (n = 6 vertebrae). RESULTS: Dose analysis was successfully performed, with generation and display of thermal dose volumes, thermal damage, dose volume histograms and isodose contours. Usability testing showed an overall positive response to the TPS as beneficial to safe and effective RFA. The in vivo porcine study showed good agreement between the manually segmented thermally damaged volumes vs. the damage volumes identified from the TPS (Dice Similarity Coefficient = 0.71 ± 0.03, Hausdorff distance = 1.2 ± 0.1 mm). CONCLUSION: A TPS specifically dedicated to RFA in the bony spine could help account for tissue heterogeneities in both thermal and electrical properties. A TPS would enable visualization of damage volumes in 2D and 3D, assisting clinicians in decisions about potential safety and effectiveness prior to performing RFA in the metastatic spine.

Femoral Antegrade Starting Tool (FAST) for intramedullary nailing.

Intramedullary (IM) nailing is the standard of care for adult lower extremity long bone fracture stabilisation. Key to this procedure is obtaining the correct entry point and trajectory for initial guide pin insertion. This work presents the Femoral Antegrade Starting Tool (FAST), a surgical tool that addresses the lack of connectivity in utilising sequential 2D fluoroscopic images to achieve 3D alignment of femoral guide pin placement. The user centred design and development of FAST is introduced and the performance of this device evaluated during guide pin insertion for femoral IM nailing in a series of sawbones and cadaveric models leading to a first in human clinical cohort study. The results demonstrated the potential of FAST to improve time and consistency of the guide pin insertion for femoral IM nailing for less experienced surgeons and trainees. Overall, FAST was found to be easy to use with a high degree of clinical interest (particularly for use in large patients) and acceptance motivating continued development of this new technology.

Determination of 3D PSFs from computed tomography reconstructed x-ray images of spherical objects and the effects of sphere radii.

PURPOSE: A method was developed to obtain three-dimensional (3D) point spread functions (PSFs) of reconstructed x-ray volumetric images using spheres of known diameters. The algorithm consists of a sphere localization step using template matching applied to the entire volume. Richardson Lucy (RL) deconvolution is used atypically to determine the PSF from the reconstructed x-ray image and a model of the sphere. The resulting PSF is arbitrary, that is, there are no assumptions of separability or symmetry. Oversampling is not used, and sample spacing matches the image. The effect of sphere radius on PSF estimate reproducibility is investigated. METHODS: Phantoms were constructed by suspending five polytetrafluoroethylene (PTFE) spheres having known radii equal to 4.77, 7.95, 9.52, 12.68, and 19.53 mm in an agar solution. The phantom included a 25 µm steel wire to calculate a line spread function (LSF). The phantom was imaged and reconstructed with a Medtronic surgical O-Arm 23 times and a Toshiba Aquilion One computed tomography (CT) 20 times. A sharp reconstruction kernel exhibiting a nonmonotonic PSF was used with the Toshiba CT. PSFs and LSFs were computed for all of the images and repeated estimates were used to compute mean and standard deviation values for every point of the PSFs and LSFs. The PSFs from spheres were converted to LSFs and compared to the wire LSF. RESULTS: The standard deviations of the PSF estimates exhibit a decreasing trend as the sphere radius is increased. The PSF from the smallest 4.77 mm sphere is the least reproducible. The normalized root mean square difference between the mean LSF derived from the 4.77 mm radius sphere and the mean wire LSF is 2.0% for the O-arm and 1.2% for the CT. CONCLUSION: Richardson Lucy (RL) deconvolution provides a method to estimate generalized (no separability or other simplifying assumptions) 3D PSFs from spheres. X-ray noise in images acquired with typical clinical protocols cause noticeable variations in PSF estimates which can be mitigated by selecting larger spheres and combining PSF estimates from different images.

3D localization of electrophysiology catheters from a single x-ray cone-beam projection.

PURPOSE: X-ray images allow the visualization of percutaneous devices such as catheters in real time but inherently lack depth information. The provision of 3D localization of these devices from cone beam x-ray projections would be advantageous for interventions such as electrophysiology (EP), whereby the operator needs to return a device to the same anatomical locations during the procedure. A method to achieve real-time 3D single view localization (SVL) of an object of known geometry from a single x-ray image is presented. svl exploits the change in the magnification of an object as its distance from the x-ray source is varied. The x-ray projection of an object of interest is compared to a synthetic x-ray projection of a model of said object as its pose is varied. METHODS: svl was tested with a 3 mm spherical marker and an electrophysiology catheter. The effect of x-ray acquisition parameters on svl was investigated. An independent reference localization method was developed to compare results when imaging a catheter translated via a computer controlled three-axes stage. svl was also performed on clinical fluoroscopy image sequences. A commercial navigation system was used in some clinical image sequences for comparison. RESULTS: svl estimates exhibited little change as x-ray acquisition parameters were varied. The reproducibility of catheter position estimates in phantoms denoted by the standard deviations, (σ(x), σ(y), σ(z)) = (0.099 mm, 0.093 mm, 2.2 mm), where x and y are parallel to the detector plane and z is the distance from the x-ray source. Position estimates (x, y, z) exhibited a 4% systematic error (underestimation) when compared to the reference method. The authors demonstrated that EP catheters can be tracked in clinical fluoroscopic images. CONCLUSIONS: It has been shown that EP catheters can be localized in real time in phantoms and clinical images at fluoroscopic exposure rates. Further work is required to characterize performance in clinical images as well as the sensitivity to clinical image quality.

Clinical apparatus for the reduction of dose area product for patients undergoing x-ray catheterization.

PURPOSE: The authors describe a design for prepatient region of interest attenuators (ROIAs) to reduce dose area product (DAP) for clinical use. The authors describe a model to predict DAP values from x-ray technique parameters recorded during a clinical procedure for image sequences obtained in the presence or absence of ROIAs. The model was developed primarily to determine what the DAP to a patient undergoing cardiac catheterization with a ROIA would have been if no ROIA had been used allowing a determination of DAP reduction. METHODS: Copper ROIAs with thicknesses that vary gradually so as not to cause significant image artifacts were constructed. X-ray image sequences were acquired on a clinical catheterization system with and without ROIAs with varying x-ray technique parameters. DAP values were measured for all said exposures using an ionization chamber and compared to a model the authors developed. RESULTS: The model can predict DAP values within 3.5% on average with or without ROIAs when compared to ionization chamber measurements. CONCLUSIONS: The proposed experimental design is adequate for measuring DAP reductions on the order of 1.5-3.5 that are expected when introducing a ROIA during patient catheterization imaging.

Model-based PSF and MTF estimation and validation from skeletal clinical CT images.

PURPOSE: A method was developed to correct for systematic errors in estimating the thickness of thin bones due to image blurring in CT images using bone interfaces to estimate the point-spread-function (PSF). This study validates the accuracy of the PSFs estimated using said method from various clinical CT images featuring cortical bones. METHODS: Gaussian PSFs, characterized by a different extent in the z (scan) direction than in the x and y directions were obtained using our method from 11 clinical CT scans of a cadaveric craniofacial skeleton. These PSFs were estimated for multiple combinations of scanning parameters and reconstruction methods. The actual PSF for each scan setting was measured using the slanted-slit technique within the image slice plane and the longitudinal axis. The Gaussian PSF and the corresponding modulation transfer function (MTF) are compared against the actual PSF and MTF for validation. RESULTS: The differences (errors) between the actual and estimated full-width half-max (FWHM) of the PSFs were 0.09 ± 0.05 and 0.14 ± 0.11 mm for the xy and z axes, respectively. The overall errors in the predicted frequencies measured at 75%, 50%, 25%, 10%, and 5% MTF levels were 0.06 ± 0.07 and 0.06 ± 0.04 cycles/mm for the xy and z axes, respectively. The accuracy of the estimates was dependent on whether they were reconstructed with a standard kernel (Toshiba's FC68, mean error of 0.06 ± 0.05 mm, MTF mean error 0.02 ± 0.02 cycles/mm) or a high resolution bone kernel (Toshiba's FC81, PSF FWHM error 0.12 ± 0.03 mm, MTF mean error 0.09 ± 0.08 cycles/mm). CONCLUSIONS: The method is accurate in 3D for an image reconstructed using a standard reconstruction kernel, which conforms to the Gaussian PSF assumption but less accurate when using a high resolution bone kernel. The method is a practical and self-contained means of estimating the PSF in clinical CT images featuring cortical bones, without the need phantoms or any prior knowledge about the scanner-specific parameters.

Generalized method for computation of true thickness and x-ray intensity information in highly blurred sub-millimeter bone features in clinical CT images.

In clinical computed tomography (CT) images, cortical bone features with sub-millimeter (sub-mm) thickness are substantially blurred, such that their thickness is overestimated and their intensity appears underestimated. Therefore, any inquiry of the geometry or the density of such bones based on these images is severely error prone. We present a model-based method for estimating the true thickness and intensity magnitude of cortical and trabecular bone layers at localized regions of complex shell bones down to 0.25 mm. The method also computes the width of the corresponding point spread function. This approach is applicable on any CT image data, and does not rely on any scanner-specific parameter inputs beyond what is inherently available in the images themselves. The method applied on CT intensity profiles of custom phantoms mimicking shell-bones produced average cortical thickness errors of 0.07 ± 0.04 mm versus an average error of 0.47 ± 0.29 mm in the untreated cases (t(55) = 10.92, p ≪ 0.001)). Similarly, the average error of intensity magnitude estimates of the method were 22 ± 2.2 HU versus an error of 445 ± 137 HU in the untreated cases (t(55) = 26.48, p ≪ 0.001)). The method was also used to correct the CT intensity profiles from a cadaveric specimen of the craniofacial skeleton (CFS) in 15 different regions. There was excellent agreement between the corrections and µCT intensity profiles of the same regions used as a 'gold standard' measure. These results set the groundwork towards restoring cortical bone geometry and intensity information in entire image data sets. This information is essential for the generation of finite element models of the CFS that can accurately describe the biomechanical behavior of its complex thin bone structures.

Ultrasound-guided identification of cardiac imaging windows.

PURPOSE: Currently, the use of cine magnetic resonance imaging (MRI) to identify cardiac quiescent periods relative to the electrocardiogram (ECG) signal is insufficient for producing submillimeter-resolution coronary MR angiography (MRA) images. In this work, the authors perform a time series comparison between tissue Doppler echocardiograms of the interventricular septum (IVS) and concurrent biplane x-ray angiograms. Our results indicate very close agreement between the diastasis gating windows identified by both the IVS and x-ray techniques. METHODS: Seven cath lab patients undergoing diagnostic angiograms were simultaneously scanned during a breath hold by ultrasound and biplane x-ray for six to eight heartbeats. The heart rate of each patient was stable. Dye was injected into either the left or right-coronary vasculature. The IVS was imaged using color tissue Doppler in an apical four-chamber view. Diastasis was estimated on the IVS velocity curve. On the biplane angiograms, proximal, mid, and distal regions were identified on the coronary artery (CA). Frame by frame correlation was used to derive displacement, and then velocity, for each region. The quiescent periods for a CA and its subsegments were estimated based on velocity. Using Pearson's correlation coefficient and Bland-Altman analysis, the authors compared the start and end times of the diastasis windows as estimated from the IVS and CA velocities. The authors also estimated the vessel blur across the diastasis windows of multiple sequential heartbeats of each patient. RESULTS: In total, 17 heartbeats were analyzed. The range of heart rate observed across patients was 47-79 beats per minute (bpm) with a mean of 57 bpm. Significant correlations (R > 0.99; p < 0.01) were observed between the IVS and x-ray techniques for the identification of the start and end times of diastasis windows. The mean difference in the starting times between IVS and CA quiescent windows was -12.0 ms. The mean difference in end times between IVS and CA quiescent windows was -3.5 ms. In contrast, the correlation between RR interval and both the start and duration of the x-ray gating windows were relatively weaker: R = 0.63 (p = 0.13) and R = 0.86 (p = 0.01). For IVS gating windows, the average estimated vessel blurs during single and multiple heartbeats were 0.5 and 0.66 mm, respectively. For x-ray gating windows, the corresponding values were 0.26 and 0.44 mm, respectively. CONCLUSIONS: In this study, the authors showed that IVS velocity can be used to identify periods of diastasis for coronary arteries. Despite variability in mid-diastolic rest positions over multiple steady rate heartbeats, vessel blurring of 0.5-1 mm was found to be achievable using the IVS gating technique. The authors envision this leading to a new cardiac gating system that, compared with conventional ECG gating, provides better resolution and shorter scan times for coronary MRA.

Characterisation of a novel porcine coronary artery CTO model.

AIMS: To create a large animal coronary chronic total occlusion (CTO) model. Presence of microvessels within the CTO lumen facilitates guidewire crossing. The patterns and time profiles of matrix changes and microvessel formation during coronary CTO maturation are unknown. METHODS AND RESULTS: CTO were created in 15 swine by percutaneous deployment of a collagen plug. Matrix changes were assessed by histology. Intraluminal neovascularisation was assessed by histology and several imaging modalities, including conventional and 3D spin angiography, micro-computed tomography (micro-CT) imaging, and contrast-enhanced magnetic resonance imaging (MRI), at six and 12 weeks following CTO creation. Matrix changes included an intense inflammatory reaction at six weeks which had partially abated by 12 weeks. A proteoglycan-rich matrix at six weeks was partially replaced with collagen by 12 weeks. Similar changes were noted in the proximal cap which was acellular. Three patterns of microvessel formation were identified and defined based on the presence and extent of a "lead" neovessel. No major differences in pattern or extent of neovascularisation were noted between six and 12 weeks. CONCLUSIONS: Heterogeneity in neovascularisation patterns occurs during coronary CTO development in a porcine model. Non-invasive imaging to determine the predominant type of neovascularisation prior to and during CTO revascularisation may improve guidewire crossing success rates. This model may be useful for further exploration of CTO pathophysiology, and may aid in further refinements of in vivo imaging of CTO and development of novel therapeutic approaches to revascularisation of CTO, such as manipulations of the proximal cap, matrix composition, neovessel induction, and device testing.

Genetic and functional aspects of linoleate isomerase in Lactobacillus acidophilus.

While the remarkable health effects of conjugated linoleic acid (CLA) catalyzed from alpha-linoleic acid by the enzyme linoleate isomerase (LI, EC 5.2.1.5) are well recognized, how widely this biochemical activity is present and the mechanisms of its regulation in lactic acid bacteria are unknown. Although certain strains of Lactobacillus acidophilus can enrich CLA in fermented dairy products, it is unknown if other strains share this capacity. Due to its immense economic importance, this work aimed to investigate genetic aspects of CLA production in L. acidophilus for the first time. The genomic DNA from industrial and type strains of L. acidophilus were subjected to PCR and immunoblot analyses using the putative LI gene of L. reuteri ATCC 55739 as probe. The CLA production ability was estimated by gas chromatography of the biomass extracts. The presumptive LI gene from L. acidophilus ATCC 832 was isolated and sequenced. The resulting sequence shared 71% identity with that of L. reuteri and at least 99% with reported sequences from other L. acidophilus strains. All the strains accumulated detectable levels of CLA and tested positive by PCR and immunoblotting. However, no apparent correlation was observed between the yields and the hybridization patterns. The results suggest that LI activity might be common among L. acidophilus and related species and provide a new tool for screening potential CLA producers.

The geometric calibration of cone-beam systems with arbitrary geometry.

A method is proposed to determine the cone-beam x-ray acquisition geometry of an imaging system using a phantom consisting of discrete x-ray opaque markers defining two parallel rings sharing a common axis. The phantom generates an image of two ellipses which are fitted to an ellipse model. A phantom-centric coordinate system is used to simplify the equations describing the ellipse coefficients such that a solution describing the acquisition geometry can be obtained via numerical optimization of only three of the nine unknown variables. We perform simulations to show how errors in the fit of the ellipse coefficients affect estimates of the acquisition geometries. These simulations show that for ellipse projections sampled with 1200 markers, 25 microm errors in marker positions and a source-detector distance (SDD) of 1.6 m, we can measure angles describing detector rotation with a mean error of <0.002 degrees and a standard deviation (SD) of <0.03 degrees. The SDD has a mean error of 0.004 mm and SD = 0.24 mm. The largest error is associated with the determination of the point on the detector closest to the x-ray source (mean error = 0.05 mm, SD = 0.85 mm). A prototype phantom was built and results from x-ray experiments are presented.

Microencapsulation of a recombinant aminopeptidase (PepN) from Lactobacillus rhamnosus S93 in chitosan-coated alginate beads.

A recombinant aminopeptidase (90 kDa) of Lactobacillus rhamnosus S93 produced by E. coli was encapsulated in alginate or chitosan-treated alginate beads prepared by an extrusion method. This study investigated the effects of alginate, CaCl2, chitosan concentrations, hardening time, pH and alginate/enzyme ratios on the encapsulation efficiency (EE) and the enzyme release (ER). Chitosan in the gelling solution significantly increased the EE from 30.2% (control) to 88.6% (coated). This polycationic polymer retarded the ER from beads during their dissolution in release buffer. An increase in alginate and chitosan concentrations led to greater EE and lesser ER from the beads. The greatest EE was observed in a pH 5.4 solution (chitosan-CaCl2) during bead formation. Increasing the CaCl2 concentration over 0.1 M neither affected the EE nor the ER. Increasing hardening time beyond 10 min led to a decrease in EE and the alginate:enzyme ratio (3 : 1) was optimal to prevent the ER.

Biotechnological methods to accelerate cheddar cheese ripening.

Cheese is one of the dairy products that can result from the enzymatic coagulation of milk. The basic steps of the transformation of milk into cheese are coagulation, draining, and ripening. Ripening is the complex process required for the development of a cheese's flavor, texture and aroma. Proteolysis, lipolysis and glycolysis are the three main biochemical reactions that are responsible for the basic changes during the maturation period. As ripening is a relatively expensive process for the cheese industry, reducing maturation time without destroying the quality of the ripened cheese has economic and technological benefits. Elevated ripening temperatures, addition of enzymes, addition of cheese slurry, attenuated starters, adjunct cultures, genetically engineered starters and recombinant enzymes and microencapsulation of ripening enzymes are traditional and modern methods used to accelerate cheese ripening. In this context, an up to date review of Cheddar cheese ripening is presented.

Polyphasic characterization of the lactic acid bacteria in kefir.

The lactic acid bacteria of kefir were isolated and characterized using phenotypical, biochemical, and genotypical methods. Polyphasic analyses of results permitted the identification of the microflora to the strain level. The genus Lactobacillus was represented by the species Lb. kefir and Lb. kefiranofaciens. Both subspecies of Lactococcus lactis (lactis and cremoris) were isolated. Leuconostoc mesenteroides subsp. cremoris was also found. The kefir studied contained few species of lactic acid bacteria but showed a high number of different strains. We found that the polyphasic analysis approach increases the confidence in strain determination. It helped confirm strain groupings and it showed that it could have an impact on the phylogeny of the strains.

Real-time image equalization for coronary X-ray angiography.

Coronary angiograms, which provide detailed images of contrast-filled coronary arteries, also show other large structures such as the diaphragm, spine and adjacent lung field. A real-time image processing method to attenuate these unwanted features is presented. Side-by-side comparisons of images selected from cine runs before and after processing show that the arteries in the processed images can be visualized more easily due to their higher contrast as other structures are made less prominent. It is also shown experimentally that this method allows more quantitative comparisons of the contrast of vessels in different parts of an image.

A lesion stabilization method for coronary angiography.

A method to make a coronary artery segment of interest appear stationary when viewing a sequence of angiographic images is proposed. The purpose of this method is to facilitate the assessment of lesions caused by coronary artery disease by improving detectability. A description of the stabilization algorithm based on template matching is given. Stabilization was performed on 41 clinical coronary angiograms exhibiting various stenoses and was successful in 39/41 cases. A quantitative analysis of stabilization errors was performed by introducing simulated moving vessels of decreasing contrast into sequences of clinical images.

Adaptive averaging for improved SNR in real-time coronary artery MRI.

A technique has been developed for combining a series of low signal-to-noise ratio (SNR) real-time magnetic resonance (MR) images to produce composite images with high SNR and minimal artifact in the presence of motion. The main challenge is identifying a set of real-time images with sufficiently small systematic differences to avoid introducing significant artifact into the composite image. To accomplish this task, one must: 1) identify images identical within the limits of noise; 2) detect systematic errors within such images with sufficient sensitivity. These steps are achieved by evaluating the correlation coefficient (CC) between regions in prospective images and a template containing the anatomy of interest. Images identical within noise are selected by comparing the measured CC values to the theoretical distribution expected due to noise. Sensitivity for systematic error depends on the SNR of the CC (=SNR(CCmax)), which in turn depends on the noise, and the template size and structure. By varying the template size, SNR(CCmax) may be altered. Experiments on phantoms and coronary artery images demonstrate that the SNR(CCmax) necessary to avoid introducing significant artifact varies with the target composite SNR. The future potential of this technique is demonstrated on high-resolution (approximately 0.9 mm), reduced field-of-view real-time coronary images.

Variable-density adaptive imaging for high-resolution coronary artery MRI.

Variable-density (VD) spiral k-space acquisitions are used to acquire high-resolution (0.78 mm), motion-compensated images of the coronary arteries. Unlike conventional methods, information for motion compensation is obtained directly from the coronary anatomy itself. Specifically, periods of minimal coronary distortion are identified by applying the correlation coefficient template matching algorithm to real-time images generated from the inner, high-density portions of the VD spirals. Combining the data associated with these images together, high-resolution, motion-compensated coronary images are generated. Because coronary motion is visualized directly, the need for cardiac-triggering, breath-holding, and navigator echoes is eliminated. The motion compensation capability of the technique is determined by the inner-spiral spatial and temporal resolution. Results indicate that the best performance is achieved using inner-spiral images with high spatial resolution (1.6-2.9 mm), even though temporal resolution (four to six independent frames per second) suffers as a result. Image quality within the template region in healthy volunteers was found to be comparable to that achieved with cardiac-triggered breath-hold scans, although extended acquisition times of around 5 min were needed to overcome reduced SNR efficiency.

A filtering method for signal equalization in region-of-interest fluoroscopy.

A method to significantly reduce the exposure area product in fluoroscopy using a pre-patient region-of-interest (ROI) attenuator is presented. The attenuator has a thin central region and a gradually increasing thickness away from the center. It is shown that the unwanted brightening artifact caused by the attenuator can be eliminated by attenuating the low spatial frequencies in the detected image using digital image processing techniques. An investigation of the best image processing method to correct for the presence of the attenuator is undertaken. The correction procedure selected is suitable for use with real-time image processors and the ROI attenuator can be permitted to move during image acquisition. Images of an anthropomorphic chest phantom acquired in the presence of the ROI attenuator using an x-ray image intensifier/video chain are corrected to illustrate the clinical feasibility of our approach.