Successful transplantation of human hepatic stem cells with restricted localization to liver using hyaluronan grafts.

Cell therapies are potential alternatives to organ transplantation for liver failure or dysfunction but are compromised by inefficient engraftment, cell dispersal to ectopic sites, and emboli formation. Grafting strategies have been devised for transplantation of human hepatic stem cells (hHpSCs) embedded into a mix of soluble signals and extracellular matrix biomaterials (hyaluronans, type III collagen, laminin) found in stem cell niches. The hHpSCs maintain a stable stem cell phenotype under the graft conditions. The grafts were transplanted into the livers of immunocompromised murine hosts with and without carbon tetrachloride treatment to assess the effects of quiescent versus injured liver conditions. Grafted cells remained localized to the livers, resulting in a larger bolus of engrafted cells in the host livers under quiescent conditions and with potential for more rapid expansion under injured liver conditions. By contrast, transplantation by direct injection or via a vascular route resulted in inefficient engraftment and cell dispersal to ectopic sites. Transplantation by grafting is proposed as a preferred strategy for cell therapies for solid organs such as the liver.

Effectiveness of the Spot tm Vision Screener With Variations in Ocular Pigments.

PURPOSE: To evaluate Spot in detecting American Association for Pediatric Ophthalmology and Strabismus (AAPOS) Amblyopia risk factors (ARF) and for ARF myopia and hyperopia with variations in ocular pigments. DESIGN: Diagnostic screening test evaluation. METHODS: Study population: Children presented for a complete eye examination in pediatric clinic. The study population included 1040 participants, of whom 273 had darkly pigmented eyes, 303 were medium pigmented, and 464 were light pigmented. INTERVENTION: Children were screened with the Spot vision screener before the complete eye examination. A pediatric ophthalmologist then completed an eye examination, including cycloplegic refraction. The pediatric ophthalmologist was blinded to the result of the Spot vision screener. MAIN OUTCOME: The association between Spot screening recommendation and meeting one or more ARF/ARF + Amblyopia criterion, Spot measured spherical equivalent, and ARF myopia and hyperopia detection. RESULTS: The area under the receiver operative characteristic curve (AUC) for myopia was excellent for all. The AUC for hyperopia was good (darker-pigmented: 0.92, medium-pigmented: 0.81, and lighter-pigmented: 0.86 eyes). The Spot was most sensitive for ARF myopia (lighter-pigmented: 0.78, medium-pigmented: 0.52, darker-pigmented: 0.49). The reverse was found for hyperopia; however, sensitivity was relatively poor. The Spot was found most sensitive for hyperopia in the darker-pigment group (0.46), 0.27 for medium-pigment, and 0.23 for the lighter-pigment cohort. CONCLUSIONS: While the Spot was confirmed as a sensitive screening test with good specificity in our large cohort, the sensitivity of the Spot in detecting AAPOS guidelines for myopia and hyperopia differed with variations in skin pigment. Our results support the consideration of ethnic and racial diversity in future advances in photorefractor technology.

Effectiveness of the Spot Vision Screener using updated 2021 AAPOS guidelines.

PURPOSE: To evaluate the Spot Vision Screener according to updated 2021 AAPOS Vision Screening Committee guidelines for instrument-based pediatric vision screen validation. METHODS: As part of an IRB-approved ongoing prospective study, children were screened with the Spot prior to a complete examination. RESULTS: Spot screening was successful in 1,036 of 1,090 children (95%). Forty-eight percent of participants were referred for further screening using the Spot manufacturer guidelines, and 40% of all children were found to have a 2021 amblyopia risk factor or visually significant refractive error by gold standard examination. The Spot recommendation compared reasonably well to the 2021 criteria, with an overall sensitivity of 0.88 and a specificity of 0.78. Applying updated guidelines to the Spot for hyperopia, anisometropia, and astigmatism yielded moderate-to-poor sensitivity (0.27-0.77) but excellent specificity (>0.9). The area under the curve of the receiver operating characteristic analysis demonstrates overall good prediction performance for the Spot for each diagnosis-myopia, hyperopia, astigmatism, anisometropia (range, 0.87-0.97). Results of our study suggest increasing the instrument referral criterion for astigmatism from 1.5 D (manufacturer thresholds of the screener used in this study) to 2 D in older children. Decreasing the anisometropia cut-off from 1 D to 0.75 D would improve sensitivity from 0.59 to >0.8. CONCLUSIONS: In our study population, the overall predictive ability of the Spot is good, with a sensitivity of 0.88 and a specificity of 0.78. We recommend specific device refractive referral criteria to maximize screening effectiveness using the updated AAPOS guidelines.

The blinq™ Vision Screener in Detection of Amblyopia and Strabismus.

PURPOSE: The blinq (Rebion Inc) is a new screening device designed to directly detect amblyopia and strabismus rather than amblyopia risk factors. We performed an independent assessment of the effectiveness of the blinq in detecting amblyopia and strabismus. DESIGN: Prospective clinical validity analysis of a screening device based on sensitivity and specificity. METHODS: Children presenting for examination in the pediatric ophthalmology clinic underwent screening with the blinq before examination by a pediatric ophthalmologist blinded to the screening results. Results of the blinq and examination findings of strabismus or amblyopia were compared. RESULTS: In our cohort of 267 children with an average age of 6.3 years, the sensitivity of the blinq to detect amblyopia or any constant strabismus was 87.5% (78.2%-93.8%) and specificity was 51.3% (43.9%-58.7%). Using the previously described "appropriate referral gold standard" criteria, including children with intermittent strabismus and high refractive error, the sensitivity increased to 91.3% and the specificity to 63.2%. We found a high number of children (44 [16%]) upon whom the blinq timed out and were included as automatic referrals. CONCLUSIONS: Our results support use of the blinq as a screening device to detect amblyopia and strabismus in children.

Interleaved acquisition for cross scatter avoidance in dual cone-beam CT.

PURPOSE: Cone-beam x-ray imaging with flat panel detectors is used for target localization in image guided radiation therapy. This imaging includes cone-beam computed tomography (CBCT) and planar imaging. Use of two orthogonal x-ray systems could reduce imaging time for CBCT, provide simultaneous orthogonal views in planar imaging, facilitate dual-energy methods, and be useful in alleviating cone-beam artifacts by providing two axially offset focal-spot trajectories. However, the potential advantages of a second cone-beam system come at the cost of cross scatter, i.e., scatter of photons originating from one tube into the noncorresponding detector. Herein, cross scatter is characterized for dual cone-beam imaging, and a method for avoiding cross scatter is proposed and evaluated. METHODS: A prototype dual-source CBCT system has been developed that models the geometry of a gantry-mounted kV imaging device used in radiation therapy. Cross scatter was characterized from 70 to 145 kVp in projections and reconstructed images using this system and three cylindrical phantoms (15, 20, and 30 cm) with a common Catphan core. A novel strategy for avoiding cross scatter in dual CBCT was developed that utilized interleaved data acquisition on each imaging chain. Interleaving, while maintaining similar angular sampling, can be achieved by either doubling the data acquisition rate or, as presented herein, halving the rotation speed. RESULTS: The ratio of cross scatter to the total detected signal was found to be as high as 0.59 in a 30 cm diameter phantom. The measured scatter-to-primary ratio in some cases exceeded 4. In the 30 cm phantom, reconstructed contrast was reduced across all ROIs by an average of 48.7% when cross scatter was present. These cross-scatter degradations were almost entirely avoided by the method of interleaved exposures. CONCLUSIONS: Cross scatter is substantial in dual cone-beam imaging, but its effects can be largely removed by interleaved acquisition, which can be achieved at the same angular sampling rate either by doubling the data acquisition rate or halving the rotation speed.

Implementation of dual-energy technique for virtual monochromatic and linearly mixed CBCTs.

PURPOSE: To implement dual-energy imaging technique for virtual monochromatic (VM) and linearly mixed (LM) cone beam CTs (CBCTs) and to demonstrate their potential applications in metal artifact reduction and contrast enhancement in image-guided radiation therapy (IGRT). METHODS: A bench-top CBCT system was used to acquire 80 kVp and 150 kVp projections, with an additional 0.8 mm tin filtration. To implement the VM technique, these projections were first decomposed into acrylic and aluminum basis material projections to synthesize VM projections, which were then used to reconstruct VM CBCTs. The effect of VM CBCT on the metal artifact reduction was evaluated with an in-house titanium-BB phantom. The optimal VM energy to maximize contrast-to-noise ratio (CNR) for iodine contrast and minimize beam hardening in VM CBCT was determined using a water phantom containing two iodine concentrations. The LM technique was implemented by linearly combining the low-energy (80 kVp) and high-energy (150 kVp) CBCTs. The dose partitioning between low-energy and high-energy CBCTs was varied (20%, 40%, 60%, and 80% for low-energy) while keeping total dose approximately equal to single-energy CBCTs, measured using an ion chamber. Noise levels and CNRs for four tissue types were investigated for dual-energy LM CBCTs in comparison with single-energy CBCTs at 80, 100, 125, and 150 kVp. RESULTS: The VM technique showed substantial reduction of metal artifacts at 100 keV with a 40% reduction in the background standard deviation compared to a 125 kVp single-energy scan of equal dose. The VM energy to maximize CNR for both iodine concentrations and minimize beam hardening in the metal-free object was 50 keV and 60 keV, respectively. The difference of average noise levels measured in the phantom background was 1.2% between dual-energy LM CBCTs and equivalent-dose single-energy CBCTs. CNR values in the LM CBCTs of any dose partitioning are better than those of 150 kVp single-energy CBCTs. The average CNR for four tissue types with 80% dose fraction at low-energy showed 9.0% and 4.1% improvement relative to 100 kVp and 125 kVp single-energy CBCTs, respectively. CNRs for low-contrast objects improved as dose partitioning was more heavily weighted toward low-energy (80 kVp) for LM CBCTs. CONCLUSIONS: Dual-energy CBCT imaging techniques were implemented to synthesize VM CBCT and LM CBCTs. VM CBCT was effective at achieving metal artifact reduction. Depending on the dose-partitioning scheme, LM CBCT demonstrated the potential to improve CNR for low contrast objects compared to single-energy CBCT acquired with equivalent dose.

Commissioning and dosimetric characteristics of TrueBeam system: composite data of three TrueBeam machines.

PURPOSE: A TrueBeam linear accelerator (TB-LINAC) is designed to deliver traditionally flattened and flattening-filter-free (FFF) beams. Although it has been widely adopted in many clinics for patient treatment, limited information is available related to commissioning of this type of machine. In this work, commissioning data of three units were measured, and multiunit comparison was presented to provide valuable insights and reliable evaluations on the characteristics of the new treatment system. METHODS: The TB-LINAC is equipped with newly designed waveguide, carousel assembly, monitoring control, and integrated imaging systems. Each machine in this study has 4, 6, 8, 10, 15 MV flattened photon beams, and 6 MV and 10 MV FFF photon beams as well as 6, 9, 12, 16, 20, and 22 MeV electron beams. Dosimetric characteristics of the three new TB-LINAC treatment units are systematically measured for commissioning. High-resolution diode detectors and ion chambers were used to measure dosimetric data for a range of field sizes from 10 × 10 to 400 × 400 mm(2). The composite dosimetric data of the three units are presented in this work. The commissioning of intensity modulated radiotherapy (IMRT), volumetric modulated arc therapy (VMAT), image-guided radiation therapy, and gating systems are also illustrated. Critical considerations of P(ion) of FFF photon beams and small field dosimetric measurements were investigated. RESULTS: The authors found all PDDs and profiles matched well among the three machines. Beam data were quantitatively compared and combined through average to yield composite beam data. The discrepancies among the machines were quantified using standard deviation (SD). The mean SD of the PDDs among the three units is 0.12%, and the mean SD of the profiles is 0.40% for 10 MV FFF open fields. The variations of P(ion) of the chamber CC13 is 1.2 ± 0.1% under 6 MV FFF and 2.0 ± 0.5% under 10 MV FFF from dmax to the 18 cm-off-axis point at 35 cm depth under 40 × 40 cm(2). The mean penumbra of crossplane flattened photon beams at collimator angle of 0° is measured from 5.88 ± 0.09 to 5.99 ± 0.13 mm from 4 to 15 MV at 10 cm depth of 100 × 100 mm(2). The mean penumbra of crossplane beams at collimator angle of 0° is measured as 3.70 ± 0.21 and 4.83 ± 0.04 mm for 6 MV FFF and 10 MV FFF, respectively, at 10 cm depth with a field size of 5 × 5 cm(2). The end-to-end test procedures of both IMRT and VMAT were performed for various energy modes. The mean ion chamber measurements of three units showed less than 2% between measurement and calculation; the mean MultiCube ICA measurements demonstrated over 90% pixels passing gamma analysis (3%, 3 mm, 5% threshold). The imaging dosimetric data of KV planar imaging and CBCT demonstrated improved consistency with vendor specifications and dose reduction for certain imaging protocols. The gated output verification showed a discrepancy of 0.05% or less between gating radiation delivery and nongating radiation delivery. CONCLUSIONS: The commissioning data indicated good consistency among the three TB-LINAC units. The commissioning data provided us valuable insights and reliable evaluations on the characteristics of the new treatment system. The systematically measured data might be useful for future reference.

Target localization using scanner-acquired SPECT data.

Target localization using single photon emission computed tomography (SPECT) and planar imaging is being investigated for guiding radiation therapy delivery. Previous studies on SPECT-based localization have used computer-simulated or hybrid images with simulated tumors embedded in disease-free patient images where the tumor position is known and localization can be calculated directly. In the current study, localization was studied using scanner-acquired images. Five fillable spheres were placed in a whole body phantom. Sphere-to-background 99mTc radioactivity was 6:1. Ten independent SPECT scans were acquired with a Trionix Triad scanner using three detector trajectories: left lateral 180°, 360°, and right lateral 180°. Scan time was equivalent to 4.5 min. Images were reconstructed with and without attenuation correction. True target locations were estimated from 12 hr SPECT and CT images. From the 12 hr SPECT scan, 45 sets of orthogonal planar images were used to assess target localization; total acquisition time per set was equivalent to 4.5min. A numerical observer localized the center of the targets in the 4.5 min SPECT and planar images. SPECT-based localization errors were compared for the different detector trajectories. Across the four peripheral spheres, and using optimal iteration numbers and postreconstruction smoothing, means and standard deviations in localization errors were 0.90 ± 0.25 mm for proximal 180° trajectories, 1.31 ± 0.51 mm for 360° orbits, and 3.93 ± 1.48 mm for distal 180° trajectories. This rank order in localization performance is predicted by target attenuation and distance from the target to the collimator. For the targets with mean localization errors < 2 mm, attenuation correction reduced localization errors by 0.15 mm on average. The improvement from attenuation correction was 1.0 mm on average for the more poorly localized targets. Attenuation correction typically reduced localization errors, but for well-localized targets, the detector trajectory generally had a larger effect. Localization performance was found to be robust to iteration number and smoothing. Localization was generally worse using planar images as compared with proximal 180° and 360° SPECT scans. Using a proximal detector trajectory and attenuation correction, localization errors were within 2 mm for the three superficial targets, thus supporting the current role in biopsy and surgery, and demonstrating the potential for SPECT imaging inside radiation therapy treatment rooms.

Imaging system QA of a medical accelerator, Novalis Tx, for IGRT per TG 142: our 1 year experience.

American Association of Physicists in Medicine (AAPM) task group (TG) 142 has recently published a report to update recommendations of the AAPM TG 40 report and add new recommendations concerning medical accelerators in the era of image-guided radiation therapy (IGRT). The recommendations of AAPM TG 142 on IGRT are timely. In our institute, we established a comprehensive imaging QA program on a medical accelerator based on AAPM TG 142 and implemented it successfully. In this paper, we share our one-year experience and performance evaluation of an OBI capable linear accelerator, Novalis Tx, per TG 142 guidelines.

Quantification of lung function on CT images based on pulmonary radiomic filtering.

PURPOSE: To develop a radiomics filtering technique for characterizing spatial-encoded regional pulmonary ventilation information on lung computed tomography (CT). METHODS: The lung volume was segmented on 46 CT images, and a 3D sliding window kernel was implemented across the lung volume to capture the spatial-encoded image information. Fifty-three radiomic features were extracted within the kernel, resulting in a fourth-order tensor object. As such, each voxel coordinate of the original lung was represented as a 53-dimensional feature vector, such that radiomic features could be viewed as feature maps within the lungs. To test the technique as a potential pulmonary ventilation biomarker, the radiomic feature maps were compared to paired functional images (Galligas PET or DTPA-SPECT) based on the Spearman correlation (ρ) analysis. RESULTS: The radiomic feature maps GLRLM-based Run-Length Non-Uniformity and GLCOM-based Sum Average are found to be highly correlated with the functional imaging. The achieved ρ (median [range]) for the two features are 0.46 [0.05, 0.67] and 0.45 [0.21, 0.65] across 46 patients and 2 functional imaging modalities, respectively. CONCLUSIONS: The results provide evidence that local regions of sparsely encoded heterogeneous lung parenchyma on CT are associated with diminished radiotracer uptake and measured lung ventilation defects on PET/SPECT imaging. These findings demonstrate the potential of radiomics to serve as a complementary tool to the current lung quantification techniques and provide hypothesis-generating data for future studies.

Crescent artifacts in cone-beam CT.

PURPOSE: In image-guided radiation therapy, cone-beam CT has been adopted for three-dimensional target localization in the treatment room. In many of these cone-beam CT images, dark and light crescent artifacts can be seen. This study investigates potential causes of this artifact and a technique for mitigating the crescents. METHODS: Three deviations from an ideal geometry were simulated to assess their ability to cause crescent artifacts: Bowtie filter sag, x-ray tube sag, and x-ray tube rotation. The magnitudes of these deviations were estimated by matching shifts in simulated projections to those observed with clinical systems. To correct the artifacts, angle-dependent blank projections were acquired and incorporated into image reconstruction. The degree of artifact reduction was evaluated with varying numbers (1-380) of blank projections. Scanner-acquired phantom and patient studies were conducted to demonstrate the effectiveness of the proposed correction method. RESULTS: All three investigated causes of the crescent artifact introduced similar mismodeling of the acquired projections and similar crescent artifacts. The deviations required for these artifacts were in the range of 0.5-5 mm or 0.1 degrees. RMS error is reduced from 8.91 x 10(-4) to 5.25 x 10(-7) for 1-380 blank projections over a 200 degrees scan angle. In the patient and phantom studies, reconstructions that utilized 380 blank projections largely mitigated the crescent artifacts. CONCLUSIONS: Small deviations from an ideal geometry can result in crescent artifacts due to steep gradients in the bowtie filter. Angle-dependent blank projections can largely alleviate the artifacts.

Direction-dependent localization errors in SPECT images.

PURPOSE: Single photon emission computed tomography (SPECT) is being investigated for imaging inside radiation therapy treatment rooms to localize biological targets. Here, computer simulations were used to analyze locational and directional dependencies in localization errors and to assess the effects of spatial resolution modeling and observer normalization on localization performance. METHODS: SPECT images of the XCAT phantom, containing 12 hot tumors, were reconstructed with detector response function compensation (DRC) and without DRC (nDRC). Numerical observers were forced to select the most suspicious tumor location, using normalized cross correlation (NXC) or un-normalized cross correlation (XC), from 3 cm diameter search volumes that each contained only one tumor. For each tumor site, localization was optimized as a function of the iteration number and postreconstruction smoothing. Localization error, the distance between true and estimated tumor positions, was calculated across the ensembles of 80 images. Direction-dependent localization bias and precision were estimated from the image ensemble. RESULTS: For the six superficial tumors in close proximity to the detector trajectory, mean localization errors were < 2 mm and were lowest or comparable using DRC-NXC, though differences from DRC-XC and nDRC-NXC were not statistically significant. DRC-NXC did provide statistically significantly better localization than nDRC-XC for five of these six tumors. At the other six sites where attenuation was more severe and the distance was generally greater between the tumor and detector, DRC typically did not show better localization than nDRC. Observer normalization improved the localization substantially for a tumor near the hotter heart. Localization errors were anisotropic and dependent on tumor location relative to the detector trajectory. CONCLUSIONS: This computer-simulation study compared localization performance for normalized and un-normalized numerical observers, which were used to estimate tumor positions in SPECT images, reconstructed with and without DRC. For tumors localized to < 2 mm on average, which are good candidates for SPECT-guided radiation therapy, localization performance typically improved by compensating for the detector response function and by using a normalized observer. The observed direction-dependent localization errors have important implications for radiation therapy and are relevant to SPECT imaging in general.

Combination of converging collimators for high-sensitivity brain SPECT.

UNLABELLED: The objective of this study, which is related to human brain SPECT, was to increase the sensitivity of a triple-camera SPECT system and reduce statistical noise in reconstructed images using a combination of converging collimators. The reason for combining collimators is to ensure both high sensitivity and sufficient sampling without trading off spatial resolution. METHODS: A high-sensitivity half-cone-beam (HCB) collimator, designed specifically for brain imaging, was combined with other collimators and compared with conventional parallel-beam and fanbeam circular orbit acquisitions. For comparison, previously studied HCB collimation with a circle-and-helix data acquisition trajectory was also included in this study. Simulations of the Hoffman 3-dimensional brain phantom were performed to calculate the efficiencies of collimators and their combinations and to quantitatively evaluate reconstruction bias, statistical noise, and signal-to-noise ratios in the reconstructed images. Experimental brain phantom data were also acquired and compared for different acquisition types. Finally, a patient brain scan was obtained with a combination of HCB and fanbeam collimators and compared with a triple-fanbeam circular orbit acquisition. RESULTS: A combination of 2 HCB collimators and 1 fanbeam collimator, compared with a triple-fanbeam collimator, can increase the photon detection efficiency by 27% and by more than a factor of 2, compared with triple-parallel-hole collimation, with equal spatial resolution measured on the axis of rotation. Quantitative analysis of reconstruction bias and visual analysis of the images showed no signs of sampling artifacts. Reconstructed images in the simulations, experimental brain phantom, and patient brain scans showed improved quality with this collimator combination due to increased sensitivity and reduced noise. Lesion visibility was also improved, as confirmed by signal-to-noise ratios. Alternatively, triple-HCB circle-and-helix acquisition has also shown competitive results, with a slight disadvantage in axial sampling and implementation procedure. CONCLUSION: Combined HCB and fanbeam collimation is a promising approach for high-sensitivity brain SPECT.

On-board SPECT for localizing functional targets: a simulation study.

Single photon emission computed tomography (SPECT) was investigated for imaging on-board radiation therapy machines in order to localize functional and molecular targets. A computer-simulated female NCAT phantom was positioned supine on a flat-top treatment couch. Twenty tumor locations were defined in the upper torso. The eight lung tumors were subject to the effects of respiratory motion. Tumor diameters of 10.8, 14.4, and 21.6 mm were simulated for tumor-to-background ratios of 3:1 and 6:1 that are characteristic of the radiotracer 99mTc-sestamibi. Projection images representing scan times of 4, 8, and 20 min were simulated for an anterior, half-circular trajectory. Images were reconstructed with attenuation correction by ordered-subsets expectation maximization (OSEM) using six subsets and five iterations. Contrast-to-noise ratios (CNRs) were calculated from ensembles of 25 images. Cross correlation with a noise-free tumor template was used to select the most suspicious tumor location within a 14.4-mm-radius search volume surrounding each tumor, with only that one tumor in each search volume. Localization accuracy was assessed by calculating average distances between measured and true tumor locations. Localization accuracy and CNRs were strongly affected by tumor location relative to the detector trajectory. For example, CNR values near the chest wall were greater by a factor of 3.5 than for tumors near the spine and posterior ribs, a much greater effect than the factor of 1.6 difference in CNR between 6:1 and 3:1 tumor uptakes. Typically, tumors of 6:1 uptake were localized as accurately with 4 min of scan time as tumors of 3:1 uptake that had been imaged for 20 min. Using 4 min scans, 14.4 and 21.6 mm anterior tumors of 6:1 uptake were localized within 2 mm. These results suggest that SPECT, on-board radiation therapy machines, may be a viable modality for localizing certain functional and molecular targets using relatively short scan times.

Tracking brachytherapy sources using emission imaging with one flat panel detector.

This work proposes to use the radiation from brachytherapy sources to track their dwell positions in three-dimensional (3D) space. The prototype device uses a single flat panel detector and a BB tray. The BBs are arranged in a defined pattern. The shadow of the BBs on the flat panel is analyzed to derive the 3D coordinates of the illumination source, i.e., the dwell position of the brachytherapy source. A kilovoltage x-ray source located 3.3 m away was used to align the center BB with the center pixel on the flat panel detector. For a test plan of 11 dwell positions, with an Ir-192 high dose rate unit, one projection was taken for each dwell point, and locations of the BB shadows were manually identified on the projection images. The 3D coordinates for the 11 dwell positions were reconstructed based on two BBs. The distances between dwell points were compared with the expected values. The average difference was 0.07 cm with a standard deviation of 0.15 cm. With automated BB shadow recognition in the future, this technique possesses the potential of tracking the 3D trajectory and the dwell times of a brachytherapy source in real time, enabling real time source position verification.

Characterizing the MTF in 3D for a Quantized SPECT Camera Having Arbitrary Trajectories.

The emergence of application-specific 3D tomographic small animal and dedicated breast imaging systems has stimulated the development of simple methods to quantify the spatial resolution or Modulation Transfer Function (MTF) of the system in three dimensions. Locally determined MTFs, obtained from line source measurements at specific locations, can characterize spatial variations in the system resolution and can help correct for such variations. In this study, a method is described to measure the MTF in 3D for a compact SPECT system that uses a 16 × 20 cm(2) CZT-based compact gamma camera and 3D positioning gantry capable of moving in different trajectories. Image data are acquired for a novel phantom consisting of three radioactivity-filled capillary tubes, positioned nearly orthogonally to each other. These images provide simultaneous measurements of the local MTF along three dimensions of the reconstructed imaged volume. The usefulness of this approach is shown by characterizing the MTF at different locations in the reconstructed imaged 3D volume using various (1) energy windows; (2) iterative reconstruction parameters including number of iterations, voxel size, and number of projection views; (3) simple and complex 3D orbital trajectories including simple vertical axis of rotation, simple tilt, complex circle-plus-arc, and complex sinusoids projected onto a hemisphere; and (4) object shapes in the camera's field of view. Results indicate that the method using the novel phantom can provide information on spatial resolution effects caused by system design, sampling, energy windows, reconstruction parameters, novel 3D orbital trajectories, and object shapes. Based on these measurements that are useful for dedicated tomographic breast imaging, it was shown that there were small variations in the MTF in 3D for various energy windows and reconstruction parameters. However, complex trajectories that uniformly sample the breast volume of interest were quantitatively shown to have slightly better spatial resolution performance than more simple orbits.

Task Group 174 Report: Utilization of [18 F]Fluorodeoxyglucose Positron Emission Tomography ([18 F]FDG-PET) in Radiation Therapy.

The use of positron emission tomography (PET) in radiation therapy (RT) is rapidly increasing in the areas of staging, segmentation, treatment planning, and response assessment. The most common radiotracer is 18 F-fluorodeoxyglucose ([18 F]FDG), a glucose analog with demonstrated efficacy in cancer diagnosis and staging. However, diagnosis and RT planning are different endeavors with unique requirements, and very little literature is available for guiding physicists and clinicians in the utilization of [18 F]FDG-PET in RT. The two goals of this report are to educate and provide recommendations. The report provides background and education on current PET imaging systems, PET tracers, intensity quantification, and current utilization in RT (staging, segmentation, image registration, treatment planning, and therapy response assessment). Recommendations are provided on acceptance testing, annual and monthly quality assurance, scanning protocols to ensure consistency between interpatient scans and intrapatient longitudinal scans, reporting of patient and scan parameters in literature, requirements for incorporation of [18 F]FDG-PET in treatment planning systems, and image registration. The recommendations provided here are minimum requirements and are not meant to cover all aspects of the use of [18 F]FDG-PET for RT.

Quantitative Evaluation of Half-Cone-Beam Scan Paths in Triple-Camera Brain SPECT.

In this study related to human brain SPECT imaging, simulation of half-cone-beam (HCB) collimation with different scan paths is performed and compared with simulated fan-beam and parallel-hole circular orbit acquisitions of disk-phantom projection data. Acquisition types are quantitatively evaluated based on the photon detection efficiency, the root-mean-squared error, contrast and signal-to-noise ratio measurements of the reconstructed images. We demonstrate that a triple-camera SPECT system with half-cone-beam collimators and circle-and-helix scan paths can offer up to a 26% efficiency increase over fan-beam, and up to a 128% increase over parallel-hole collimators for equal spatial resolutions, and display no visible axial sampling artifacts in reconstructed disk-phantom images. In addition, we perform qualitative experimental evaluation of triple-HCB circle-and-helix acquisition using a Hoffman 3D brain phantom. Reconstructed brain phantom images show improved quality due to reduced noise and no apparent sampling artifacts. Triple-HCB circle-and-helix SPECT has a potential for improved brain imaging, producing higher image quality with a smaller reconstruction error and better lesion detectability due to increased efficiency for equal spatial resolution compared to conventional fan-beam and parallel-hole SPECT.

Brain SPECT Simulation Using Half-Cone-Beam Collimation and Single-Revolution Helical-Path Acquisition.

In this study related to human brain SPECT imaging, simulation of half-cone-beam collimation and helical-path data acquisition is performed. We discuss problems related to circular-orbit acquisition using cone-beam collimation, such as shoulder interference resulting in object truncation, and insufficient sampling of the object resulting in axial distortions in the reconstructed images. We demonstrate that a triple-camera SPECT system with half-cone-beam collimation and single-revolution helical-path acquisition eliminates both issues and offers substantially improved sampling and almost artifact-free reconstruction of the object.

Impact of moving target on measurement accuracy in 3D and 4D PET imaging-a phantom study.

PURPOSE: The purpose of this study was to evaluate the impact of tumor motion on maximum standardized uptake value (SUVmax) and metabolic tumor volume (MTV) measurements in both 3-dimensional and respiratory-correlated, 4-dimensional positron emission tomography (PET) imaging. We also evaluated the effect of implementing different attenuation correction methods in 4-dimensional PET image reconstruction on SUVmax and MTV. METHODS AND MATERIALS: An anthropomorphic thorax phantom with a spherical ball as a surrogate for a tumor was used. Different types of motion were imposed on the ball to mimic a patient's breathing motion. Three-dimensional PET imaging of the phantom without tumor motion was performed and used as the reference. The ball was then set in motion with different breathing motion traces and imaged with both 3- and 4-dimensional PET methods. The clinical 4-dimensional PET imaging protocol was modified so that 3 different types of attenuation correction images were used for reconstructions: the same free-breathing computed tomography (CT) for all PET phases, the same average intensity projection CT for all PET phases, and 4-dimensional CT for phase-matched attenuation correction. Tumor SUVmax and MTV values that were measured from the moving phantom were compared with the reference values. RESULTS: SUVmax that was measured in 3-dimensional PET imaging was different from the reference value by 20.4% on average for the motions that were investigated; this difference decreased to 2.6% with 4-dimensional PET imaging. The measurement of MTV in 4-dimensional PET also showed a similar magnitude of reduction of deviation compared with 3-dimensional PET. Four-dimensional PET with use of phase-matched 4-dimensional CT for attenuation correction showed less variation in SUVmax and MTV among phases compared with 4-dimensional PET with free-breathing CT or average intensity projection CT for attenuation correction. CONCLUSIONS: Four-dimensional PET imaging reduces the impact of motion on measured SUVmax and MTV when compared with 3-dimensional PET imaging. Clinical 4-dimensional PET imaging protocols should consider phase-matched 4-dimensional CT imaging for attenuation correction to achieve more accurate measurements.