Translational Correction Research Articles

The Panflute Technique: Novel 3D-Printed Patient Specific Instrumentation to Guide Curved Intra-Articular Osteotomies for Tibial Plateau Malunions.

Background/Objectives: 3D patient-specific corrective osteotomies are optimized for use with oscillating saws, thereby rendering it incapable of executing curved osteotomies. The aim of this technical note is to introduce and evaluate the Panflute technique, which facilitates curved osteotomies with precise depth control for intra-articular corrective osteotomies in posttraumatic tibial plateau malunions. Methods: A 33-year-old male patient with an intra-articular malunion was treated one year after index surgery of a lateral split-depression tibial plateau fracture with the Panflute technique. The guide design allowed for multiple drill trajectories in a curved path, recreating the original fracture lines. Cylindrical drill tubes in the guide were tailored to match bone trajectory length. This resulted in a patient-specific Panflute-like design enabling precise depth control, safeguarding posterior neurovascular structures. Secondly, the recreated fragment was reduced with a reduction guide, applied to the plate in situ, to facilitate reposition using the plate as tool and reference. Results: The procedure went without technical drawbacks or surgical complications. Postoperative assessment showed that repositioning of the osteotomized articular fragment was performed accurately: pre- to postoperative translational corrections were 5.4 to 0.5 mm posterior displacement for AP deformity (x-axis); 2.9 to 1.0 mm lateral to medial reduction (y-axis); and 5.9 to 0.6 mm cranial-caudal correction (z-axis). Clinically, at 3 months, the fracture united, the patient regained full flexion, and valgus defect-laxity resolved. Conclusions: The presented Panflute-osteotomy guide allows for a pre-planned curved osteotomy. Additionally, for every drill trajectory, the depth could be controlled. The proposed method may expand our surgical armamentarium of patient-specific 3D techniques and solutions for complex intra-articular osteotomies.

3D B1+ corrected simultaneous myocardial T1 and T1ρ mapping with subject-specific respiratory motion correction and water-fat separation.

To develop a 3D free-breathing cardiac multi-parametric mapping framework that is robust to confounders of respiratory motion, fat, and B1+ inhomogeneities and validate it for joint myocardial T1 and T1ρ mapping at 3T. An electrocardiogram-triggered sequence with dual-echo Dixon readout was developed, where nine cardiac cycles were repeatedly acquired with inversion recovery and T1ρ preparation pulses for T1 and T1ρ sensitization. A subject-specific respiratory motion model relating the 1D diaphragmatic navigator to the respiration-induced 3D translational motion of the heart was constructed followed by respiratory motion binning and intra-bin 3D translational and inter-bin non-rigid motion correction. Spin history B1+ inhomogeneities were corrected with optimized dual flip angle strategy. After water-fat separation, the water images were matched to the simulated dictionary for T1 and T1ρ quantification. Phantoms and 10 heathy subjects were imaged to validate the proposed technique. The proposed technique achieved strong correlation (T1: R2 = 0.99; T1ρ: R2 = 0.98) with the reference measurements in phantoms. 3D cardiac T1 and T1ρ maps with spatial resolution of 2 × 2 × 4 mm were obtained with scan time of 5.4 ± 0.5 min, demonstrating comparable T1 (1236 ± 59 ms) and T1ρ (50.2 ± 2.4 ms) measurements to 2D separate breath-hold mapping techniques. The estimated B1+ maps showed spatial variations across the left ventricle with the septal and inferior regions being 10%-25% lower than the anterior and septal regions. The proposed technique achieved efficient 3D joint myocardial T1 and T1ρ mapping at 3T with respiratory motion correction, spin history B1+ correction and water-fat separation.

Non-covalent interactions and charge transfer in the CO activation by low-valent group 14 complexes.

The CO activation by low-valent group 14 catalysts encompasses the rupture of varied covalent bonds in a single transition state through a concerted pathway. The bond between the central main group atom and the hydride in the complex is elongated to trigger the formation of the C-H bond with CO accompanied by the concomitant formation of the E-O bond between the complex and CO to lead the corresponding formate product. Prior studies have established that besides the apolar nature of CO , its initial interaction with the complex is primarily governed by electrostatic interactions. Notably, other stabilizing interactions and the transfer of charge between catalysts and CO during the initial phases of the reaction have been ignored. In this study, we have quantified the non-covalent interactions and charge transfer that facilitate the activation of CO by group 14 main group complex. Our findings indicate that electrostatic interactions predominantly stabilize the complex and CO in the reactant region. However, induction energy becomes the main stabilizing force as the reaction progresses towards the transition state, surpassing electrostatics. Induction contributes about 50% to the stabilization at the transition state, followed by electrostatics (40%) and dispersion interactions (10%). Atomic charges calculated with the minimal basis iterative stockholder (MBIS) method reveal larger charge transfer for the back-side reaction path in which CO approaches the catalysts in contrast to the front-side approach. Notably, it was discovered that a minor initial bending of CO to approximately initiates the charge transfer process for all systems. Furthermore, our investigation of group 14 elements demonstrates a systematic reduction in both activation energies and charge transfer to CO while descending in group 14. All studied reactions were characterized along the reaction coordinate obtained with the intrinsic reaction coordinate (IRC) methodology at the M06-2X/6-31g(d,p) level of theory. Gibbs free energy in toluene was computed using electronic energies at the DLPNO-CCSD(T)/cc-pVTZ-SSD(E) level of theory. Vibrational and translational entropy corrections were applied to provide a more accurate description of the obtained Gibbs free energies. To better characterize the changes in the reaction coordinate for all reactions, the reaction force analysis (RFA) has been employed. It enables the partition of the reaction coordinate into the reactant, transition state, and product regions where different stages of the mechanism occur. A detailed characterization of the main non-covalent driving forces in the initial stages of the activation of CO by low-valent group 14 complexes was performed using symmetry-adapted perturbation theory (SAPT). The SAPT0-CT/def2-SVP method was employed for these computations. Charge transfer descriptors based on atomic population using the MBIS scheme were also obtained to complement the SAPT analyses.

Simulation of translational motion correction during cartesian brain MRI

Brain Magnetic Resonance Imaging (MRI) is invaluable for non-invasively capturing detailed anatomical and functional information. However, motion artifacts, particularly during brain imaging, can compromise the precision of scans. This study explores motion correction techniques, focusing on the widely-used PROPELLER method and its application to Golden-angle Cartesian Randomized Time-resolved (GOCART) acquisition. While PROPELLER effectively corrects in-plane translation and rotation, its use with cartesian data demands increased sampling. GOCART, a high-speed cartesian sampling scheme, has shown promise in Dynamic Contrast-Enhanced (DCE) MRI, yet its specific artifacts in brain imaging remain underexplored. Our simulation framework assesses PROPELLER correction for translational motion in GOCART-sampled data, examining two motion directions, varied frequencies, and different temporal resolutions. Serving as a vital pre-clinical testing tool, this platform contributes to the optimization of motion correction algorithms, addressing challenges and refining imaging protocols for enhanced diagnostic reliability in advanced brain MRI.

Image guidance and interfractional anatomical variation in paediatric abdominal radiotherapy.

To identify variables predicting interfractional anatomical variations measured with cone-beam CT (CBCT) throughout abdominal paediatric radiotherapy, and to assess the potential of surface-guided radiotherapy (SGRT) to monitor these changes. Metrics of variation in gastrointestinal (GI) gas volume and separation of the body contour and abdominal wall were calculated from 21 planning CTs and 77 weekly CBCTs for 21 abdominal neuroblastoma patients (median 4 years, range: 2 - 19 years). Age, sex, feeding tubes, and general anaesthesia (GA) were explored as predictive variables for anatomical variation. Furthermore, GI gas variation was correlated with changes in body and abdominal wall separation, as well as simulated SGRT metrics of translational and rotational corrections between CT/CBCT. GI gas volumes varied 74 ± 54 ml across all scans, while body and abdominal wall separation varied 2.0 ± 0.7 mm and 4.1 ± 1.5 mm from planning, respectively. Patients < 3.5 years (p = 0.04) and treated under GA (p < 0.01) experienced greater GI gas variation; GA was the strongest predictor in multivariate analysis (p < 0.01). Absence of feeding tubes was linked to greater body contour variation (p = 0.03). GI gas variation correlated with body (R = 0.53) and abdominal wall (R = 0.63) changes. The strongest correlations with SGRT metrics were found for anterior-posterior translation (R = 0.65) and rotation of the left-right axis (R = -0.36). Young age, GA, and absence of feeding tubes were linked to stronger interfractional anatomical variation and are likely indicative of patients benefiting from adaptive/robust planning pathways. Our data suggest a role for SGRT to inform the need for CBCT at each treatment fraction in this patient group. This is the first study to suggest the potential role of SGRT for the management of internal interfractional anatomical variation in paediatric abdominal radiotherapy.

High-resolution, respiratory-resolved coronary MRA using a Phyllotaxis-reordered variable-density 3D cones trajectory

PurposeTo develop a respiratory-resolved motion-compensation method for free-breathing, high-resolution coronary magnetic resonance angiography (CMRA) using a 3D cones trajectory. MethodsTo achieve respiratory-resolved 0.98 mm resolution images in a clinically relevant scan time, we undersample the imaging data with a variable-density 3D cones trajectory. For retrospective motion compensation, translational estimates from 3D image-based navigators (3D iNAVs) are used to bin the imaging data into four phases from end-expiration to end-inspiration. To ensure pseudo-random undersampling within each respiratory phase, we devise a phyllotaxis readout ordering scheme mindful of eddy current artifacts in steady state free precession imaging. Following binning, residual 3D translational motion within each phase is computed using the 3D iNAVs and corrected for in the imaging data. The noise-like aliasing characteristic of the combined phyllotaxis and cones sampling pattern is leveraged in a compressed sensing reconstruction with spatial and temporal regularization to reduce aliasing in each of the respiratory phases. ResultsIn initial studies of six subjects, respiratory motion compensation using the proposed method yields improved image quality compared to non-respiratory-resolved approaches with no motion correction and with 3D translational correction. Qualitative assessment by two cardiologists and quantitative evaluation with the image edge profile acutance metric indicate the superior sharpness of coronary segments reconstructed with the proposed method (P < 0.01). ConclusionWe have demonstrated a new method for free-breathing, high-resolution CMRA based on a variable-density 3D cones trajectory with modified phyllotaxis ordering and respiratory-resolved motion compensation with 3D iNAVs.

The spatial accuracy of ring-mounted halcyon linac versus C-arm TrueBeam linac for single-isocenter/multi-target SBRT treatment.

Stereotactic body radiotherapy (SBRT) treatment of oligometastatic lesions via single-isocenter/multi-target (SIMT) plan is more efficient than using multi-isocenter/multitarget SBRT. This study quantifies the spatial positioning accuracy of 2 commercially available LINAC systems for SIMT treatment pertaining to the potential amplification of error as a function of the target's distance-to-isocenter. We compare the Ring-Gantry Halcyon LINAC equipped with the fast iterative conebeam-CT (iCBCT) for image-guided SIMT treatment, and the SBRT-dedicated C-Arm TrueBeam with standard pretreatment CBCT imaging. For both systems, Sun Nuclear's MultiMet Winston-Lutz Cube phantom with 6 metallic BBs distributed at different planes up to 7 cm away from the isocenter was used. The phantom was aligned and imaged via CBCT, and then couch corrections were applied. To treat all 6 BBs, an Eclipse 10-field 3D-conformal Field-in-Field (2×2 cm2 MLC field to each BB) plan for varying gantry, collimator, and couch (TrueBeam only) positions was developed for both machines with 6MV-FFF beam. The plan was delivered through ARIA once a week. The EPID images were analyzed via Sun Nuclear's software for spatial positioning accuracy. On TrueBeam, the treatment plan was delivered twice: once with 3DoF translational corrections and once with PerfectPitch 6DoF couch corrections. The average 3D spatial positioning accuracy was 0.55 ± 0.30 mm, 0.54 ± 0.24 mm, and 0.56 ± 0.28 mm at isocenter, and 0.59 ± 0.30 mm, 0.69 ± 0.30 mm, and 0.70 ± 0.35 mm at 7 cm distance-to-isocenter for Halcyon, TrueBeam 3DoF, and TrueBeam 6DoF, respectively. This suggests there are no clinically significant deviations of spatial uncertainty between the platforms with the distance-to-isocenter. On both platforms, our weekly independent measurements demonstrated the reproducibility for less than 1.0 mm positional accuracy of off-axis targets up to 7 cm from the isocenter. Due to this, no additional PTV-margin is suggested for lesions within 7 cm of isocenter. This study confirms that Halcyon can deliver similar positional accuracy to SBRT-dedicated TrueBeam to off-axis targets up to 7 cm from isocenter. These results further benchmark the spatial uncertainty of our extensively used SBRT-dedicated TrueBeam LINAC for SIMT SBRT treatments.

The dosimetric error due to uncorrected tumor rotation during real-time adaptive prostate stereotactic body radiation therapy.

During prostate stereotactic body radiation therapy (SBRT), prostate tumor translational motion may deteriorate the planned dose distribution. Most of the major advances in motion management to date have focused on correcting this one aspect of the tumor motion, translation. However, large prostate rotation up to 30° has been measured. As the technological innovation evolves toward delivering increasingly precise radiotherapy, it is important to quantify the clinical benefit of translational and rotational motion correction over translational motion correctionalone. The purpose of this work was to quantify the dosimetric impact of intrafractional dynamic rotation of the prostate measured with a six degrees-of-freedom tumor motion monitoringtechnology. The delivered dose was reconstructed including (a) translational and rotational motion and (b) only translational motion of the tumor for 32 prostate cancer patients recruited on a 5-fraction prostate SBRT clinical trial. Patients on the trial received 7.25 Gy in a treatment fraction. A 5 mm clinical target volume (CTV) to planning target volume (PTV) margin was applied in all directions except the posterior direction where a 3 mm expansion was used. Prostate intrafractional translational motion was managed using a gating strategy, and any translation above the gating threshold was corrected by applying an equivalent couch shift. The residual translational motion is denoted as . Prostate intrafractional rotational motion was recorded but not corrected. The dose differences from the planned dose due to + , ΔD( + ) and due to alone, ΔD( ), were then determined for CTV D98, PTV D95, bladder V6Gy, and rectum V6Gy. The residual dose error due to uncorrected rotation, was then quantified: = ΔD( + ) - ΔD( ). Fractional data analysis shows that the dose differences from the plan (both ΔD( + ) and ΔD( )) for CTV D98 was less than 5% in all treatment fractions. ΔD( + ) was larger than 5% in one fraction for PTV D95, in one fraction for bladder V6Gy, and in five fractions for rectum V6Gy. Uncorrected rotation, induced residual dose error, , resulted in less dose to CTV and PTV in 43% and 59% treatment fractions, respectively, and more dose to bladder and rectum in 51% and 53% treatment fractions, respectively. The cumulative dose over five fractions, ∑D( + ) and ∑D( ), was always within 5% of the planned dose for all four structures for everypatient. The dosimetric impact of tumor rotation on a large prostate cancer patient cohort was quantified in this study. These results suggest that the standard 3-5 mm CTV-PTV margin was sufficient to account for the intrafraction prostate rotation observed for this cohort of patients, provided an appropriate gating threshold was applied to correct for translational motion. Residual dose errors due to uncorrected prostate rotation were small in magnitude, which may be corrected using different treatment adaptation strategies to further improve the dosimetricaccuracy.

Quantitative Relaxometry for Target Localization and Response Assessment in Ultra-Hypofractionated MR-Guided Radiotherapy to the Prostate and DIL

<h3>Purpose/Objective(s)</h3> MR-guided systems, such as hybrid MR-Linacs, provide a novel platform for the acquisition and development of image-based biomarkers that can provide crucial information during daily online plan adaptation. Relaxometry has been shown to be sensitive to changes in tissue composition or function during radiotherapy. We investigate the added value of longitudinal relaxometry for target localization and response assessment. <h3>Materials/Methods</h3> The study included 42 unfavorable intermediate risk prostate patients undergoing ultra-hypofractionated MR-guided adaptive therapy to the prostate and seminal vesicles CTV with an integrated boost to the dominant intraprostatic lesion (DIL). The prescription was 800/900 cGy x 5 fractions, every other day. The longitudinal (T1) and transverse (T2) relaxation times were measured in the MR-Linac. T1 maps were acquired using the variable flip-angle method: TR/TE=20/2.3 ms, FA={4°, 22°}, FOV=320 × 320 × 200 mm, voxel = 0.7 × 0.7 × 3 mm³, scan time = 1.5 min. T2 maps were acquired using the multi-echo spin-echo method: TR/TE/ΔTE = 4000/22/11 ms, 8 echoes, FOV = 320 × 320 × 100 mm, voxel = 0.5 × 0.5 × 3 mm³, scan time = 5.5 min. The bias and reproducibility of T1/T2 mapping was assessed over the course of eight weeks using a NIST-traceable phantom. Longitudinal phantom measurements were also used to establish baseline values for T1/T2. The analysis was implemented in the Computational Environment for Radiotherapy Research. Daily T1 and T2 maps of prostate patients were rigidly registered to the pre-beam online-planning T2w images and T1/T2 values were analyzed within the CTV/DIL contours. <h3>Results</h3> The median bias with respect to nominal values for T1, T2 was -1.1%, 3.4%. When compared to baseline, the median bias for T1, T2 was 0.6%, 0.1% and the coefficient of variation was 2.1%, 0.9%, respectively. Maximum translation and rotation corrections within the T1/T2 maps were 1.9±0.3mm and 0.9°±0.2°. Across all patients and fractions, T1_CTV=1766±150ms, T1_DIL=1559±245ms, T2_CTV=127±19ms, T2_DIL=111±19ms. T1 and T2 were significantly longer in the CTV. Variations over fraction number are shown in Table 1. Linear regression showed there is a significant increase of mean T1 in the DIL (p=0.05) and CTV (p=0.05). The increase in T1 from fraction 1 to fraction 5 was 12.3% and 6.3% in DIL and CTV, respectively. The trend for T2 was not significant for either DIL or CTV. <h3>Conclusion</h3> T1 and T2 quantitative relaxometry is a surrogate measure of unbound water content and motility and shows the potential to serve as a predictor for changes in the local tumor microenvironment during MR-guided adaptive radiotherapy.

Accelerated 3D free-breathing high-resolution myocardial T1ρ mapping at 3Tesla.

To develop a fast free-breathing whole-heart high-resolution myocardial T1ρ mapping technique with robust spin-lock preparation that can be performed at 3Tesla. An adiabatically excited continuous-wave spin-lock module, insensitive to field inhomogeneities, was implemented with an electrocardiogram-triggered low-flip angle spoiled gradient echo sequence with variable-density 3D Cartesian undersampling at a 3 Tesla whole-body scanner. A saturation pulse was performed at the beginning of each cardiac cycle to null the magnetization before T1ρ preparation. Multiple T1ρ -weighted images were acquired with T1ρ preparations with different spin-lock times in an interleaved fashion. Respiratory self-gating approach was adopted along with localized autofocus to enable 3D translational motion correction of the data acquired in each heartbeat. After motion correction, multi-contrast locally low-rank reconstruction was performed to reduce undersampling artifacts. The accuracy and feasibility of the 3D T1ρ mapping technique was investigated in phantoms and in vivo in 10 healthy subjects compared with the 2D T1ρ mapping. The 3D T1ρ mapping technique provided similar phantom T1ρ measurements in the range of 25-120 ms to the 2D T1ρ mapping reference over a wide range of simulated heart rates. With the robust adiabatically excited continuous-wave spin-lock preparation, good quality 2D and 3D in vivo T1ρ -weighted images and T1ρ maps were obtained. Myocardial T1ρ values with the 3D T1ρ mapping were slightly longer than 2D breath-hold measurements (septal T1ρ : 52.7 ± 1.4ms vs. 50.2 ± 1.8ms, P < 0.01). A fast 3D free-breathing whole-heart T1ρ mapping technique was proposed for T1ρ quantification at 3T with isotropic spatial resolution (2 mm3 ) and short scan time of ∼4.5min.

Dosimetry Between CBCT-Guided Translational Correction vs MR-Guided Online Adaptation for Prostate Ultra-Hypofractionated Radiotherapy

Purpose: Ultra-hypofractionated (³6Gy/fraction) radiotherapy for localized prostate cancer is delivered using daily image-guidance, with either Conebeam-CT (CBCT) or Magnetic Resonance Imaging (MRI). CBCT-Linac allows pre-delivery 3 degrees of freedom (3DOF) translation correction whereas MR-Linac enables treatment adaptation based on daily anatomy. Herein, we compared the dose to prostate and organs at risk (OARs) by these two systems.

Experimental investigation of dynamic real-time rotation-including dose reconstruction during prostate tracking radiotherapy.

BackgroundHypofractionation in prostate radiotherapy is of increasing interest. Steep dose gradients and a large weight on each individual fraction emphasize the need for motion management. Real‐time motion management techniques such as multileaf collimator (MLC) tracking or couch tracking typically adjust for translational motion while rotations remain uncompensated with unknown dosimetric impact.PurposeThe purpose of this study is to demonstrate and validate dynamic real‐time rotation‐including dose reconstruction during radiotherapy experiments with and without MLC and couch tracking.MethodsReal‐time dose reconstruction was performed using the in‐house developed software DoseTracker. DoseTracker receives streamed target positions and accelerator parameters during treatment delivery and uses a pencil beam algorithm with water density assumption to reconstruct the dose in a moving target. DoseTracker's ability to reconstruct motion‐induced dose errors in a dynamically rotating and translating target was investigated during three different scenarios: (1) no motion compensation and translational motion correction with (2) MLC tracking and (3) couch tracking.In each scenario, dose reconstruction was performed online and in real time during delivery of two dual‐arc volumetric‐modulated arc therapy prostate plans with a prescribed fraction dose of 7 Gy to the prostate and simultaneous intraprostatic lesion boosts with doses of at least 8 Gy, but up to 10 Gy as long as the organs at risk dose constraints were fulfilled. The plans were delivered to a pelvis phantom that replicated three patient‐measured motion traces using a rotational insert with 21 layers of EBT3 film spaced 2.5 mm apart. DoseTracker repeatedly calculated the actual motion‐including dose increment and the planned static dose increment since the last calculation in 84 500 points in the film stack. The experiments were performed with a TrueBeam accelerator with MLC and couch tracking based on electromagnetic transponders embedded in the film stack.The motion‐induced dose error was quantified as the difference between the final cumulative dose with motion and without motion using the 2D 2%/2 mm γ‐failure rate and the difference in dose to 95% of the clinical target volume (CTV ΔD 95%) and the gross target volume (GTV ΔD 95%) as well as the difference in dose to 0.1 cm3 of the urethra, bladder, and rectum (ΔD 0.1CC). The motion‐induced errors were compared between dose reconstructions and film measurements.ResultsThe dose was reconstructed in all calculation points at a mean frequency of 4.7 Hz. The root‐mean‐square difference between real‐time reconstructed and film‐measured motion‐induced errors was 3.1%‐points (γ‐failure rate), 0.13 Gy (CTV ΔD 95%), 0.23 Gy (GTV ΔD 95%), 0.19 Gy (urethra ΔD 0.1CC), 0.09 Gy (bladder ΔD 0.1CC), and 0.07 Gy (rectum ΔD 0.1CC).ConclusionsIn a series of phantom experiments, online real‐time rotation‐including dose reconstruction was performed for the first time. The calculated motion‐induced errors agreed well with film measurements. The dose reconstruction provides a valuable tool for monitoring dose delivery and investigating the efficacy of advanced motion‐compensation techniques in the presence of translational and rotational motion.

Non-rigid motion-corrected free-breathing 3D myocardial Dixon LGE imaging in a clinical setting

ObjectivesTo investigate the efficacy of an in-line non-rigid motion-compensated reconstruction (NRC) in an image-navigated high-resolution three-dimensional late gadolinium enhancement (LGE) sequence with Dixon water–fat separation, in a clinical setting.MethodsForty-seven consecutive patients were enrolled prospectively and examined with 1.5 T MRI. NRC reconstructions were compared to translational motion-compensated reconstructions (TC) of the same datasets in overall and different sub-category image quality scores, diagnostic confidence, contrast ratios, LGE pattern, and semiautomatic LGE quantification.ResultsNRC outperformed TC in all image quality scores (p < 0.001 to 0.016; e.g., overall image quality 5/5 points vs. 4/5). Overall image quality was downgraded in only 23% of NRC datasets vs. 53% of TC datasets due to residual respiratory motion. In both reconstructions, LGE was rated as ischemic in 11 patients and non-ischemic in 10 patients, while it was absent in 26 patients. NRC delivered significantly higher LGE-to-myocardium and blood-to-myocardium contrast ratios (median 6.33 vs. 5.96, p < 0.001 and 4.88 vs. 4.66, p < 0.001, respectively). Automatically detected LGE mass was significantly lower in the NRC reconstruction (p < 0.001). Diagnostic confidence was identical in all cases, with high confidence in 89% and probable in 11% datasets for both reconstructions. No case was rated as inconclusive.ConclusionsThe in-line implementation of a non-rigid motion-compensated reconstruction framework improved image quality in image-navigated free-breathing, isotropic high-resolution 3D LGE imaging with undersampled spiral-like Cartesian sampling and Dixon water–fat separation compared to translational motion correction of the same datasets. The sharper depictions of LGE may lead to more accurate measures of LGE mass.Key Points• 3D LGE imaging provides high-resolution detection of myocardial scarring.• Non-rigid motion correction provides better image quality in cardiac MRI.• Non-rigid motion correction may lead to more accurate measures of LGE mass.

Interaction between a non-concentric rigid sphere immersed in a micropolar fluid and a spherical envelope with slip regime

A semi-analytical investigation of a quiescent micropolar fluid between a rigid sphere and a non-concentric spherical envelope with a slip regime is obtained. Two different cases have been considered one is the hydrodynamic drag strength and the translational wall correction factor (TWCF) exerted by the fluid on the inner sphere are proportional to the translational velocities and the second is the hydrodynamic torque and the rotational wall correction factor (RWCF) are applied to the inner sphere which is proportional to the angular velocities. The numerical solution is composed of the superposition of the fundamental solutions in the two spherical coordinate systems setups on the poles of the rigid sphere and the spherical envelope by using a collocation scheme. The boundary conditions, slip, and spin-slip are presented on the sphere’s surfaces. The results were achieved numerically with excellent convergence for the parameters, size ratio, separation distance, micropolarity parameter, slip, slip-spin parameters. Limiting cases are agreeable with the obtainable results in the literature.

CBCT Verification of SRT for Patients With Brain Metastases.

BackgroundThe aim of our work is to demonstrate the role of image guidance and volumetric imaging in stereotactic radiotherapy (SRT) of brain metastases.MethodsBetween 2018 and 2020, 106 patients underwent intracranial stereotactic radiotherapy. 10 patients with metastatic brain tumors treated with SRT were randomly selected and included in our study model. Patients were scanned pre- and post-treatment with cone beam CT. Total of 100 verifications of 50 stereotaxic treatments were performed and analyzed.ResultsPopulation mean X, Y, Z values were -0.13 cm, -0.04 cm, -0.03 cm, respectively, rotation values 0.81°, 0.51°, 0.46°, respectively. Systematic error components for translational displacements pre corrections were as follows: 0.14 cm for X, 0.13 cm for Y and 0.1 cm for Z. Systematic error components of the post-treatment HR 3D CBCTs were as follows: 0.01 cm for X, 0.06 cm for Y and 0.04 cm for Z.ConclusionsPopulation mean values close to 0 confirmed that there is no systematic variation in our system and the accuracy of our equipment and tools is reliable. HR 3D CBCT scans performed pre SRTs further refine patient and target volume setting, support medical decision making and eliminate the possibility of gross error.

Whole-heart non-rigid motion corrected coronary MRA with autofocus virtual 3D iNAV

PurposeRespiratory motion-corrected coronary MR angiography (CMRA) has shown promise for assessing coronary disease. By incorporating coronal 2D image navigators (iNAVs), respiratory motion can be corrected for in a beat-to-beat basis using translational correction in the foot-head (FH) and right-left (RL) directions and in a bin-to-bin basis using non-rigid motion correction addressing the remaining FH, RL and anterior-posterior (AP) motion. However, with this approach beat-to-beat AP motion is not corrected for. In this work we investigate the effect of remaining beat-to-beat AP motion and propose a virtual 3D iNAV that exploits autofocus motion correction to enable beat-to-beat AP and improved RL intra-bin motion correction. MethodsFree-breathing 3D whole-heart CMRA was acquired using a 3-fold undersampled variable-density Cartesian trajectory. Beat-to-beat 3D translational respiratory motion was estimated from the 2D iNAVs in FH and RL directions, and in AP direction with autofocus assuming a linear relationship between FH and AP movement of the heart. Furthermore, motion in RL was also refined using autofocus. This virtual 3D (v3D) iNAV was incorporated in a non-rigid motion correction (NRMC) framework. The proposed approach was tested in 12 cardiac patients, and visible vessel length and vessel sharpness for the right (RCA) and left (LAD) coronary arteries were compared against 2D iNAV-based NRMC. ResultsAverage vessel sharpness and length in v3D iNAV NRMC was improved compared to 2D iNAV NRMC (vessel sharpness: RCA: 56 ± 1% vs 52 ± 11%, LAD: 49 ± 8% vs 49 ± 7%; visible vessel length: RCA: 5.98 ± 1.37 cm vs 5.81 ± 1.62 cm, LAD: 5.95 ± 1.85 cm vs 4.83 ± 1.56 cm), however these improvements were not statistically significant. ConclusionThe proposed virtual 3D iNAV NRMC reconstruction further improved NRMC CMRA image quality by reducing artefacts arising from residual AP motion, however the level of improvement was subject-dependent.

Benchmark ab initio proton affinity and gas-phase basicity of α-alanine based on coupled-cluster theory and statistical mechanics.

We determine the proton affinity (PA) and gas-phase basicity (GB) of amino acid α-alanine at a chemically accurate level by performing explicitly-correlated CCSD(T)-F12b/aug-cc-pVDZ geometry optimizations and normal mode vibrational frequency calculations as well as CCSD(T)-F12b/aug-cc-pVTZ energy computations at the possible neutral and protonated geometries. Temperature effects at 298.15 K considering translational, rotational, and vibrational enthalpy and entropy corrections are obtained via standard statistical mechanics utilizing the molecular geometries and the harmonic vibrational energy levels. Both the amino nitrogen (N) and the carbonyl oxygen (O) atoms are proven to be potential protonation sites and a systematic conformational search reveals 3 N- and 9 O-protonated conformers in the 0.00-7.88 and 25.43-30.43 kcal/mol energy ranges at 0K, respectively. The final computed PA and GB values at (0)298.15 K in case of N-protonation are (214.47)216.80 and 207.07 kcal/mol, respectively, whereas the corresponding values for O-protonation are (189.04)190.63 and 182.31 kcal/mol. The results of the benchmark high-level coupled-cluster computations are utilized to assess the accuracy of several lower-level cost-effective methods such as MP2 and density functional theory with various functionals (SOGGA11-X, M06-2X, PBE0, B3LYP, M06, TPSS).

153: A Dosimetric Comparison Between Translational Correction with CBCT-Guidance and Adaptation Using MR-Linac for Prostate Ultra-Hypofractionated Radiotherapy

153: A Dosimetric Comparison Between Translational Correction with CBCT-Guidance and Adaptation Using MR-Linac for Prostate Ultra-Hypofractionated Radiotherapy

Frameless immobilization system with roll correction for stereotactic radiosurgery of intracranial brain metastases.

The objectives of this study were to develop a frameless immobilization system that allows roll rotation corrections and to investigate the performance of this system for stereotactic radiosurgery (SRS) treatment. We designed the support frame of a frameless immobilization system based on the commercial Brainlab immobilization system. The support frame consisted of a fixed component and a rotating component. With rack and pinion gears and guide holes installed in the system, the rotating component was configured to be rotated along the longitudinal axis of the patient with respect to the fixed component. To evaluate the performance of the system, the six degree-of-freedom (6D) positioning corrections (translational and rotational corrections) were assessed by image verification between planning computed tomography (CT) and cone-beam computed tomography (CBCT) images. The commercial immobilization system was evaluated in the same manner for comparison. The mean translational shifts for the commercial system were 0.68 ± 0.19mm, 0.73 ± 0.24mm and 0.78 ± 0.19mm, while those for the developed system were 0.44 ± 0.31mm, 0.43 ± 0.25mm and 0.60 ± 0.14mm in the lateral, longitudinal and vertical directions, respectively. The mean rotational shifts for the commercial system were 0.37° ± 0.12°, 0.32° ± 0.16° and 0.38° ± 0.14°, while those for the developed system were 0.04° ± 0.04°, 0.11° ± 0.06° and 0.15° ± 0.12° along the lateral, vertical and longitudinal axes of the patient, respectively. For institutions that do not have 6D robotic couches installed, the use of the developed immobilization system can provide 6D corrections, resulting in shorter treatment times and higher patient positioning accuracy.

Motion compensated whole-heart coronary cardiovascular magnetic resonance angiography using focused navigation (fNAV)

BackgroundRadial self-navigated (RSN) whole-heart coronary cardiovascular magnetic resonance angiography (CCMRA) is a free-breathing technique that estimates and corrects for respiratory motion. However, RSN has been limited to a 1D rigid correction which is often insufficient for patients with complex respiratory patterns. The goal of this work is therefore to improve the robustness and quality of 3D radial CCMRA by incorporating both 3D motion information and nonrigid intra-acquisition correction of the data into a framework called focused navigation (fNAV).MethodsWe applied fNAV to 500 data sets from a numerical simulation, 22 healthy subjects, and 549 cardiac patients. In each of these cohorts we compared fNAV to RSN and respiratory resolved extradimensional golden-angle radial sparse parallel (XD-GRASP) reconstructions of the same data. Reconstruction times for each method were recorded. Motion estimate accuracy was measured as the correlation between fNAV and ground truth for simulations, and fNAV and image registration for in vivo data. Percent vessel sharpness was measured in all simulated data sets and healthy subjects, and a subset of patients. Finally, subjective image quality analysis was performed by a blinded expert reviewer who chose the best image for each in vivo data set and scored on a Likert scale 0–4 in a subset of patients by two reviewers in consensus.ResultsThe reconstruction time for fNAV images was significantly higher than RSN (6.1 ± 2.1 min vs 1.4 ± 0.3, min, p < 0.025) but significantly lower than XD-GRASP (25.6 ± 7.1, min, p < 0.025). Overall, there is high correlation between the fNAV and reference displacement estimates across all data sets (0.73 ± 0.29). For simulated data, healthy subjects, and patients, fNAV lead to significantly sharper coronary arteries than all other reconstruction methods (p < 0.01). Finally, in a blinded evaluation by an expert reviewer fNAV was chosen as the best image in 444 out of 571 data sets (78%; p < 0.001) and consensus grades of fNAV images (2.6 ± 0.6) were significantly higher (p < 0.05) than uncorrected (1.7 ± 0.7), RSN (1.9 ± 0.6), and XD-GRASP (1.8 ± 0.8).ConclusionfNAV is a promising technique for improving the quality of RSN free-breathing 3D whole-heart CCMRA. This novel approach to respiratory self-navigation can derive 3D nonrigid motion estimations from an acquired 1D signal yielding statistically significant improvement in image sharpness relative to 1D translational correction as well as XD-GRASP reconstructions. Further study of the diagnostic impact of this technique is therefore warranted to evaluate its full clinical utility.