Respiratory Gating Research Articles

The Characteristics of Respiratory Compensation Strategy and Its Application Equipment Analysis

Background: Thoracic and abdominal tumors seriously endanger people's health. In the process of accurate diagnosis and treatment, due to the existence of respiratory motion, the location of the tumor will change. to solve this problem, many experts and scholars have proposed a variety of respiratory compensation strategies. However, there is a lack of comprehensive introduction and analysis of various respiratory compensation strategies. Objective: According to the characteristics of respiratory compensation, this paper discusses its development status and development trend, and puts forward reasonable suggestions for its future development, to provide a reference for other researchers. Methods: Through the analysis of a large number of articles and patents. Classification, advantages and disadvantages, and main application equipment of the existing respiratory compensation strategies are introduced. Application principle, influencing factors, main application equipment, and compensation accuracy of breath holding method, abdominal pressure method, active respiratory control method, respiratory gating method and tumor real-time tracking method were compared and analyzed. Results: Through the comparison and analysis of various respiratory compensation strategies, the characteristics, applicable conditions, and existing problems of various respiratory compensation strategies are clarified. The solutions to the existing problems are put forward, and the development trend of respiratory compensation strategies is prospected. Conclusion: Respiratory compensation strategy plays an important role in the diagnosis and treatment of thoracic and abdominal tumors. Various existing respiratory compensation strategies can effectively compensate for respiratory movement, but they all face the problem of insufficient compensation accuracy. Therefore, it is necessary to study and improve the respiratory compensation strategy. In the future, respiratory compensation strategies will develop in the direction of better effect and more comfortable for patients.

Pharyngeal airway dimensions and adipose distribution in the minipig.

To evaluate the pharyngeal airway dimensions and regional pharyngeal adipose distribution in the young adult minipig model. Eight 7-8-months-old Yucatan minipigs, half male and female, were sedated and placed prone to scan the pharyngeal region. Magnetic resonance imaging (MRI) was performed using dynamic turbo-field echo (TFE)-sequence with respiratory gating and adipose-weighted sequence. Respiratory airflow velocity, pressure, and volume were also recorded. The sizes of velopharyngeal and oropharyngeal airway, and retroglossal areas were measured coronally during inspiration and expiration. The airway volumes from the nasal cavity to the retroglossal space were segmented, reconstructed, and evaluated in sagittal views. The adipose distribution in the tongue base, soft palate, pharyngeal wall, tongue body, and masseter muscle (reference) were segmented and measured in sagittal and coronal planes. The velopharyngeal and oropharyngeal areas were larger in inspiration than in expiration. These areas were also larger than that in the retroglossal space (p<0.05). The nasal cavity showed a larger volume than that of the pharyngeal regions (p<0.05). The adipose distribution was larger in the posterior region of the tongue base and anterior soft palate, both larger than the masseter muscle (p<0.05). The larger oropharyngeal dimensions and increased adipose distribution in the tongue base contribute to the functional morphology of the pharyngeal airway in the healthy minipig. These data provide the baseline for further analysis in enlarged and reduced tongue base minipig models.

Validation and clinical impact of motion-free PET imaging using data-driven respiratory gating and elastic PET-CT registration.

Clinical whole-body (WB) PET images can be compensated for respiratory motion using data-driven gating (DDG). However, PET DDG images may still exhibit motion artefacts at the diaphragm if the CT is acquired in a different respiratory phase than the PET image. This study evaluates the combined use of PET DDG and a deep-learning model (AIR-PETCT) for elastic registration of CT (WarpCT) to the non attenuation- and non scatter-corrected PET image (PET NAC), enabling improved PET reconstruction. The validation cohort included 20 patients referred for clinical FDG PET/CT, undergoing two CT scans: a free respiration CTfree and an end-expiration breath-hold CTex. AIR-PETCT registered each CT to the PET NAC and PET DDG NAC images. The image quality of PET and PET DDG images reconstructed using CTs and WarpCTs was evaluated by three blinded readers. Additionally, a clinical impact cohort of 20 patients with significant "banana" artefacts from FDG, PSMA, and DOTATOC scans was assessed for image quality and tumor-to-background ratios. AIR-PETCT was robust and generated consistent WarpCTs when registering different CTs to the same PET NAC. The use of WarpCT instead of CT consistently led to equivalent or improved PET image quality. The algorithm significantly reduced "banana" artefacts and improved lesion-to-background ratios around the diaphragm. The blinded clinicians clearly preferred PET DDG images reconstructed using WarpCT. AIR-PETCT effectively reduces respiratory motion artefacts from PET images, while improving lesion contrast. The combination of PET DDG and WarpCT holds promise for clinical application, improving PET image evaluation and diagnostic confidence.

A Respiratory Signal Monitoring Method Based on Dual‐Pathway Deep Learning Networks in Image‐Guided Robotic‐Assisted Intervention System

ABSTRACTBackgroundPercutaneous puncture procedures, guided by image‐guided robotic‐assisted intervention (IGRI) systems, are susceptible to disruptions in patients' respiratory rhythm due to factors such as pain and psychological distress.MethodsWe developed an IGRI system with a coded structured light camera and a binocular camera. Our system incorporates dual‐pathway deep learning networks, combining convolutional long short‐term memory (ConvLSTM) and point long short‐term memory (PointLSTM) modules for real‐time respiratory signal monitoring.ResultsOur in‐house dataset experiments demonstrate the superior performance of the proposed network in accuracy, precision, recall and F1 compared to separate use of PointLSTM and ConvLSTM for respiratory pattern classification.ConclusionIn our IGRI system, a respiratory signal monitoring module was constructed with a binocular camera and dual‐pathway deep learning networks. The integrated respiratory monitoring module provides a basis for the application of respiratory gating technology to IGRI systems and enhances surgical safety by security mechanisms.

Dosimetric calibration of anatomy-specific ultra-high dose rate electron irradiation platform for preclinical FLASH radiobiology experiments.

FLASH radiation therapy (RT) offers a promising avenue for the broadening of the therapeutic index. However, to leverage the full potential of FLASH in the clinical setting, an improved understanding of the biological principles involved is critical. This requires the availability of specialized equipment optimized for the delivery of conventional (CONV) and ultra-high dose rate (UHDR) irradiation for preclinical studies. One method to conduct such preclinical radiobiological research involves adapting a clinical linear accelerator configured to deliver both CONV and UHDR irradiation. We characterized the dosimetric properties of a clinical linear accelerator configured to deliver ultra-high dose rate irradiation to two anatomic sites in mice and for cell-culture FLASH radiobiology experiments. Delivered doses of UHDR electron beams were controlled by a microcontroller and relay interfaced with the respiratory gating system. We also produced beam collimators with indexed stereotactic mouse positioning devices to provide anatomically specific preclinical treatments. Treatment delivery was monitored directly with an ionization chamber, and charge measurements were correlated with radiochromic film measurements at the entry surface of the mice. The setup for conventional dose rate irradiation utilized the same collimation system but at increased source-to-surface distance. Monte Carlo simulations and film dosimetry were used to characterize beam properties and dose distributions. The mean electron beam energies before the flattening filter were 18.8 MeV (UHDR) and 17.7 MeV (CONV), with corresponding values at the mouse surface of 17.2 and 16.2 MeV. The charges measured with an external ion chamber were linearly correlated with the mouse entrance dose. The use of relay gating for pulse control initially led to a delivery failure rate of 20% (±1 pulse); adjustments to account for the linac latency improved this rate to<1/20. Beam field sizes for two anatomically specific mouse collimators (4 × 4 cm2 for whole-abdomen and 1.5 × 1.5 cm2 for unilateral lung irradiation) were accurate within<5% and had low radiation leakage (<4%). Normalizing the dose at the center of the mouse (∼0.75cm depth) produced UHDR and CONV doses to the irradiated volumes with>95% agreement. We successfully configured a clinical linear accelerator for increased output and developed a robust preclinical platform for anatomically specific irradiation, with highly accurate and precise temporal and spatial dose delivery, for both CONV and UHDR irradiation applications.

Feasibility, classification and potential clinical impact of non-invasive delineation of abdominal lymphatic vessels in patients following TCPC with T2 weighted MRI

Recent research in patients with functionally univentricular hearts (UVH) is focusing on pathologies of the lymphatic vessels. Morphology of the abdominal lymphatic vessels was analyzed by MRI in patients with UVH following total cavopulmonary connection (TCPC) and it was examined, if clinical and laboratory parameters correlate with changes after TCPC. We prospectively examined 33 patients at the age of 19.8 (14.6;30.2) years [median (Q1;Q3)] after TCPC (follow-up 14.3 years (9.7;24.9) with a heavily T2-weighted MRI sequence on a 3.0 T scanner. Examinations in coronal orientation were performed with respiratory gating, slice thickness 0.6 mm, TR 2400 ms, TE 692 ms, FoV 460 mm (covering thoracic and abdominal regions), scan time 14:41 min (13:18;16:30) after a solid meal and a cup of pineapple juice. The findings were classified according to delineation of abdominal lymphatic vessels. Type 1: <3 abdominal vessels (av) definable; type 2: 4–6 av definable; type 3: >6 av and/or oedematous changes or ascites. The results were correlated with parameters obtained at the annual routine check-up. Statistical analysis was performed using U-test and Chi-square test. Fifteen patients (group 1) showed type 3 lymphatic morphologies, two of which had ascites. Eighteen patients (group 2) showed lower grade morphologies (type 1–2). Image quality was rated considering the delineation of the common hepatic duct and did not differ between groups (p = 0.134). “Lymphatic burden” was automatically examined and was indexed to the number of delineated abdominal vessels and showed quantification according to the chosen categories type 1–3. Patients in group 1 were younger at MRI examination (17.4;14.3/18.9 vs. 26.2;18.2/32.3 years, p = 0.03). Superior cavopulmonary connection (SCPC) had been performed earlier in group 1 (9.9;7.9/25.5 vs. 29.2;13.7/66.6 months, p = 0.018). Laboratory examinations in group 1 showed lower levels for Immunoglobulin G (IgG), Lipase, α-Antitrypsin, Cystatin C and TSH. There were no significant differences for total protein, NTproBNP, lymphocytes or platelets. A history of chylothorax was present in 7/15 versus 2/18 p = 0.022. Protein-losing enteropathy (PLE) occurred in 4/15 versus 1/18 (p = 0.092). T2 weighted MRI is feasible for noninvasive delineation of abdominal lymphatic vessel in patients following TCPC. In the long-term follow-up, patients with more pronounced changes of the abdominal lymphatic vessels were younger at SCPC and were more likely to show a history of chylothorax and lower IgG values.

Ungated, plug-and-play preclinical cardiac CEST-MRI using radial FLASH with segmented saturation.

Electrocardiography (ECG) and respiratory-gated preclinical cardiac CEST-MRI acquisitions are difficult because of variable saturation recovery with T1, RF interference in the ECG signal, and offset-to-offset variation in Z-magnetization and cardiac phase introduced by changes in cardiac frequency and trigger delays. The proposed method consists of segmented saturation modules with radial FLASH readouts and golden angle progression. The segmented saturation blocks drive the system to steady-state, and because center k-space is sampled repeatedly, steady-state saturation dominates contrast during gridding and reconstruction. Ten complete Z-spectra were acquired in healthy mice using both ECG and respiratory-gated and ungated methods. Z-spectra were also acquired at multiple saturation B1 values to optimize for amide and Cr contrasts. There was no significant difference between CEST contrasts (amide, Cr, magnetization transfer) calculated from images acquired using ECG and respiratory-gated and ungated methods (p = 0.27, 0.11, 0.47). A saturation power of 1.8μT provides optimal contrast amplitudes for both amide and total Cr contrast without significantly complicating CEST contrast quantification because of water direct saturation, magnetization transfer, and RF spillover between amide and Cr pools. Further, variability in CEST contrast measurements was significantly reduced using the ungated radial FLASH acquisition (p = 0.002, 0.006 for amide and Cr, respectively). This method enables CEST mapping in the murine myocardium without the need for cardiac or respiratory gating. Quantitative CEST contrasts are consistent with those obtained using gated sequences, and per-contrast variance is significantly reduced. This approach makes preclinical cardiac CEST-MRI easily accessible, even for investigators without prior experience in cardiac imaging.

A Comprehensive and Repeatable Contrast-Enhanced Ultrasound Quantification Approach for Clinical Evaluations of Tumor Blood Flow.

The aim of this study is to define a comprehensive and repeatable contrast-enhanced ultrasound (CEUS) imaging protocol and analysis method to quantitatively assess lesional blood flow. Easily repeatable CEUS evaluations are essential for longitudinal treatment monitoring. The quantification method described here aims to provide a structure for future clinical studies. This retrospective analysis study included liver CEUS studies in 80 patients, 40 of which contained lesions (primarily hepatocellular carcinoma, n = 28). Each patient was given at least 2 injections of a microbubble contrast agent, and 60-second continuous loops were acquired for each injection to enable evaluation of repeatability. For each bolus injection, 1.2 mL of contrast was delivered, whereas continuous, stationary scanning was performed. Automated respiratory gating and motion compensation algorithms dealt with breathing motion. Similar in size regions of interest were drawn around the lesion and liver parenchyma, and time-intensity curves (TICs) with linearized image data were generated. Four bolus transit parameters, rise time (RT), mean transit time (MTT), peak intensity (PI), and area under the curve (AUC), were extracted either directly from the actual TIC data or from a lognormal distribution curve fitted to the TIC. Interinjection repeatability for each parameter was evaluated with coefficient of variation. A 95% confidence interval was calculated for all fitted lognormal distribution curve coefficient of determination (R2) values, which serves as a data quality metric. One-sample t tests were performed between values obtained from injection pairs and between the fitted lognormal distribution curve and direct extraction from the TIC calculation methods to establish there were no significant differences between injections and measurement precision, respectively. Average interinjection coefficient of variation with both the fitted curve and direct calculation of RT and MTT was less than 21%, whereas PI and AUC were less than 40% for lesion and parenchyma regions of interest. The 95% confidence interval for the R2 value of all fitted lognormal curves was [0.95, 0.96]. The 1-sample t test for interinjection value difference showed no significant differences, indicating there was no relationship between the order of the repeated bolus injections and the resulting parameters. The 1-sample t test between the values from the fitted lognormal distribution curve and the direct extraction from the TIC calculation found no statistically significant differences (α = 0.05) for all perfusion-related parameters except lesion and parenchyma PI and lesion MTT. The scanning protocol and analysis method outlined and validated in this study provide easily repeatable quantitative evaluations of lesional blood flow with bolus transit parameters in CEUS data that were not available before. With vital features such as probe stabilization ideally performed with an articulated arm and an automated respiratory gating algorithm, we were able to achieve interinjection repeatability of blood flow parameters that are comparable or surpass levels currently established for clinical 2D CEUS scans. Similar values and interinjection repeatability were achieved between calculations from a fitted curve or directly from the data. This demonstrated not only the strength of the protocol to generate TICs with minimal noise, but also suggests that curve fitting might be avoided for a more standardized approach. Utilizing the imaging protocol and analysis method defined in this study, we aim for this methodology to potentially assist clinicians to assess true perfusion changes for treatment monitoring with CEUS in longitudinal studies.

Enhancement of the lymphatic system following intravenous administration of ferumoxytol.

Lymphatic imaging is becoming increasingly important in the management of patients with congenital heart disease. However, the influence of the intravenous contrast agent ferumoxytol on lymphatic imaging is not well understood. To evaluate the impact of intravenous ferumoxytol on T1-weighted and T2-weighted lymphatic imaging in patients with congenital heart disease. We included consecutive patients receiving ferumoxytol-enhanced 3D angiography for congenital heart disease evaluation. The visibility of the thoracic duct was reviewed on the T1-weighted 3D inversion recovery balanced-steady-state free precession (SSFP) with respiratory navigator gating sequence which is routinely used for angiography and the heavily T2-weighted turbo spin echo sequence which is employed for lymphatic imaging. Data on demographics and time interval between contrast administration and imaging were collected. Statistical analyses were performed using t-tests for continuous variables and chi-squared tests for categorical variables. One hundred nineteen consecutive patients with a mean age of 12.46 years±7.7 years were included. Of these, 45 cases underwent both T1-weighted and T2-weighted imaging; the other 74 underwent only T1-weighted imaging. Of the 45 patients, 20 had thoracic duct enhancement on T1-weighted imaging; among the 26 sedated, only 2 showed enhancement, while 18 of 19 non-sedated patients showed enhancement (P<0.001), indicating a strong association between sedation and reduced thoracic duct visibility. If T2-weighted imaging was performed after contrast administration, the thoracic duct was not visible on those images. For all 45 cases of visible thoracic duct in the entire cohort, the time from contrast administration to imaging ranged from 8 min up to 75 min. The enhancement of the thoracic lymphatic duct on T1-weighted imaging, coupled with degradation observed on T2-weighted imaging, suggests that intravenously administered ferumoxytol rapidly enters the lymphatic fluid. To prevent T2 shortening from degrading the imaging results, T2-weighted imaging for lymphatic evaluation should be performed prior to the administration of ferumoxytol. Sedation and, by inference, fasting may influence this property and warrant further investigation in future studies.

375: Comparison of set up error in SBRT lung between AlignRT and Respiratory Gating (RPM) by using CBCT

375: Comparison of set up error in SBRT lung between AlignRT and Respiratory Gating (RPM) by using CBCT

2634: Quality Assurance of respiratory gating with Hexamotion system

2634: Quality Assurance of respiratory gating with Hexamotion system

Feasibility of a deep-inspiration breath-hold [18F]AlF-NOTA-LM3 PET/CT imaging on upper-abdominal lesions in NET patients: in comparison with respiratory-gated PET/CT

PurposesTo explore the clinical feasibility and efficacy of a deep inspiration breath-hold (BH) PET/CT using [18F]AlF-NOTA-LM3 on upper abdominal lesions in patients with neuroendocrine tumors (NETs).MethodsTwenty-three patients underwent a free-breath (FB) whole-body PET/CT, including a 10 min/bed scan for the upper abdomen with a vital signal monitoring for respiratory gating (RG) followed by a 20-second BH PET/CT covering the same axial range. For the upper abdomen bed, the following PET series was reconstructed: a 2-min FB PET; RG PET (6 bins); a 20-second and 15-second BH PET (BH_15 and BH_20). Semi-quantitative analysis was performed to compare liver SUVmean, lesion SUVmax, MTV, its percentage difference and target-to-background ratio (TBR) between both BH PET and RG PET images. Subgroup analysis considered lesion location, MTV and SUVmax. A 5-point Likert scale was used to perform visual analysis and any missed or additional lesions were identified compared with RG PET.ResultsQuantitative analysis on overall lesions (n = 78) revealed higher SUVmax and TBR, and smaller MTV for both BH PET compared to FB and RG PET, with lesion location-specific variations. Neither significant difference was observed in all metrics between RG and FB PET in larger lesions, nor in MTV in lower-uptake lesions. However, both BH PET significantly enhanced these measurements. In the visual analysis, both BH PET showed noninferior performance to RG PET, and were evaluated clinically acceptable. Additional and missed lesions were observed in FB and both BH PET compared with RG PET, but didn’t alter the clinical management. The BH_15 PET showed comparable performance to BH_20 PET in any comparison.ConclusionThe BH PET/CT using [18F]AlF-NOTA-LM3 is effective in detecting upper abdominal lesions, offering more accurate quantitative measurements. Using a novel PET/CT scanner, a 15-second BH PET can provide comparable and superior performance to RG PET, indicating potential feasibility in clinical routines.

High-speed bioimpedance-based gating system for radiotherapy: Prototype and proof of principle.

To investigate a novel bioimpedance-based respiratory gating system (BRGS) designed for external beam radiotherapy and to evaluate its technical characteristics in comparison with existing similar systems. The BRGS was tested on three healthy volunteers in free breathing and breath-hold patterns under laboratory conditions. Its parameters, including the time delay (TD) between the actual impedance change and the gating signal, temperature drift, root mean square (RMS) noise, and signal-to-noise ratio (SNR), were measured and analyzed. The gate-on TD and the gate-off TD were found to be 9.0±2.0ms [mean±standard deviation (M±SD)] and 7.2±1.3ms, respectively. The temperature drift of the BRGS output signal was 0.02 Ω after 30 min of operation. RMS noise averaged 0.14±0.05 Ω (M±SD) for all subjects and varied from 0.08 to 0.20 Ω with repeated measurements. A significant difference in SNR (p<0.001) was observed between subjects, ranging from 4 to 15. The evaluated bioimpedance-based gating system showed a high performance in real-time respiratory monitoring and may potentially be used as an external surrogate guidance for respiratory-gated external beam radiotherapy. Direct comparison with commercially available systems, 4D correlation studies, and expansion of the patient sample are goals for future preclinical studies.

Data driven surrogate signal extraction for dynamic PET using selective PCA: time windows versus the combination of components

Objective. Respiratory motion correction is beneficial in positron emission tomography (PET), as it can reduce artefacts caused by motion and improve quantitative accuracy. Methods of motion correction are commonly based on a respiratory trace obtained through an external device (like the real time position management system) or a data driven method, such as those based on dimensionality reduction techniques (for instance principal component analysis (PCA)). PCA itself being a linear transformation to the axis of greatest variation. Data driven methods have the advantage of being non-invasive, and can be performed post-acquisition. However, their main downside being that they are adversely affected by the tracer kinetics of the dynamic PET acquisition. Therefore, they are mostly limited to static PET acquisitions. This work seeks to extend on existing PCA-based data-driven motion correction methods, to allow for their applicability to dynamic PET imaging. Approach. The methods explored in this work include; a moving window approach (similar to the Kinetic Respiratory Gating method from Schleyer et al (2014)), extrapolation of the principal component from later time points to earlier time points, and a method to score, select, and combine multiple respiratory components. The resulting respiratory traces were evaluated on 22 data sets from a dynamic [18F]-FDG study on patients with idiopathic pulmonary fibrosis. This was achieved by calculating their correlation with a surrogate signal acquired using a real time position management system. Main results. The results indicate that all methods produce better surrogate signals than when applying conventional PCA to dynamic data (for instance, a higher correlation with a gold standard respiratory trace). Extrapolating a late time point principal component produced more promising results than using a moving window. Scoring, selecting, and combining components held benefits over all other methods. Significance. This work allows for the extraction of a surrogate signal from dynamic PET data earlier in the acquisition and with a greater accuracy than previous work. This potentially allows for numerous other methods (for instance, respiratory motion correction) to be applied to this data (when they otherwise could not be previously used).

Stationary prospective cardiac gated computed tomography—dynamic study in phantoms and in vivo

Objective. This study explores the feasibility of a stationary gantry cardiac gated computed tomography (CT) with carbon nanotube (CNT) linear x-ray source arrays. Approach. We developed a stationary gantry CT system utilizing multipixel CNT x-ray sources. Given the advantages of straightforward x-ray pulse control with these sources, we investigated the potential for gated prospective imaging. We implemented prospective respiratory and cardiac gating control and evaluated the system through dynamic phantom imaging studies followed by imaging of a porcine model. Main Results. The findings revealed minimal anatomical motion artifacts in the heart and lungs, confirming successful physiologic gated acquisition in stationary gantry cardiac CT. This indicates the potential of this imaging approach for reducing artifacts and improving image quality. Significance. This study demonstrates the feasibility of prospective physiological gating with CNT x-ray sources in a stationary gantry setup for cardiac imaging. This approach could potentially alleviate the need for beta blocker administration during cardiac CT scans, thereby increasing the flexibility of the imaging system and enabling the imaging of a wider variety of patient cardiac conditions.

MRI retrospective respiratory gating and cardiac sensing by CW Doppler radar: A feasibility study.

This study investigates the feasibility of non-contact retrospective respiratory gating and cardiac sensing using continuous wave Doppler radar deployed in an MRI system. The proposed technique can complement existing sensors which are difficult to apply for certain patient populations. We leverage a software-defined radio for continuous wave radar at 2.4 GHz to detect in-vivo respiratory and cardiac timescrolled signals. In-bore radar signal demodulation is verified with full electromagnetic simulations, and its functionality is validated on a test bench and within the MR bore with four normal subjects. Radar sensing was compared against well-known references: electrocardiography on a test bench, system bellows, and pulsed plethysmography sensors with in the MRI bore. The feasibility of noncontact cardiac rate sensing, dynamic breathing sequence synchronization, and in-bore motion correction for retrospective respiratory gating applications was demonstrated. Optimal radar front-end system arrangement, along with spectral isolation and narrow bandwidth of operation, enable MRI-compatible and interference-free motion sensing. The signal-to-noise-ratio degradation by the radar integration was within 4.5% on phantom images. We confirmed that in-bore retrospective motion correction using CW Doppler radar is feasible without MRI system constraints. Non-contact motion correction sensing in MRI may provide better patient handling and through put by complementing existing system sensors and motion correction algorithms.

T1-weighted Motion Mitigation in Abdominal MRI: Technical Principles, Clinical Applications, Current Limitations, and Future Prospects.

T1-weighted (T1W) pulse sequences are an indispensable component of clinical protocols in abdominal MRI but usually require multiple breath holds (BHs) during the examination, which not all patients can sustain. Patient motion can affect the quality of T1W imaging so that key diagnostic information, such as intrinsic signal intensity and contrast enhancement image patterns, cannot be determined. Patient motion also has a negative impact on examination efficiency, as multiple acquisition attempts prolong the duration of the examination and often remain noncontributory. Techniques for mitigation of motion-related artifacts at T1W imaging include multiple arterial acquisitions within one BH; free breathing with respiratory gating or respiratory triggering; and radial imaging acquisition techniques, such as golden-angle radial k-space acquisition (stack-of-stars). While each of these techniques has inherent strengths and limitations, the selection of a specific motion-mitigation technique is based on several factors, including the clinical task under investigation, downstream technical ramifications, patient condition, and user preference. The authors review the technical principles of free-breathing motion mitigation techniques in abdominal MRI with T1W sequences, offer an overview of the established clinical applications, and outline the existing limitations of these techniques. In addition, practical guidance for abdominal MRI protocol strategies commonly encountered in clinical scenarios involving patients with limited BH abilities is rendered. Future prospects of free-breathing T1W imaging in abdominal MRI are also discussed. ©RSNA, 2024 See the invited commentary by Fraum and An in this issue.

Comparison of the variability and diagnostic efficacy of respiratory-gated PET/CT based radiomics features with ungated PET/CT in lung lesions

ObjectivesTo investigate the variability and diagnostic efficacy of respiratory-gated (RG) PET/CT based radiomics features compared to ungated (UG) PET/CT in the differentiation of non-small cell lung cancer (NSCLC) and benign lesions. Methods117 patients with suspected lung lesions from March 2020 to May 2021 and consent to undergo UG PET/CT and chest RG PET/CT (including phase-based quiescent period gating, pQPG and phase-matched 4D PET/CT, 4DRG) were prospectively included. 377 radiomics features were extracted from PET images of each scan. Paired t test was used to compare UG and RG features for inter-scan variability analysis. We developed three radiomics models with UG and RG features (i.e. UGModel, pQPGModel and 4DRGModel). ROC curves were used to compare diagnostic efficiencies, and the model-level comparison of diagnostic value was performed by five-fold cross-validation. A P value < 0.05 was considered as statistically significant. ResultsA total of 111 patients (average age ± standard deviation was 59.1 ± 11.6 y, range, 29 – 88 y, and 63 were males) with 209 lung lesions were analyzed for features variability and the subgroup of 126 non-metastasis lesions in 91 patients without treatment before PET/CT were included for diagnosis analysis. 101/377 (26.8 %) 4DRG features and 82/377 (21.8 %) pQPG features showed significant difference compared to UG features (both P<0.05). 61/377 (16.2 %) and 59/377 (15.6 %) of them showed significantly better discriminant ability (ΔAUC% (i.e. (AUCRG – AUCUG) / AUCUG×100 %) > 0 and P<0.05) in malignant recognition, respectively. For the model-level comparison, 4DRGModel achieved the highest diagnostic efficacy (sen 73.2 %, spe 87.3 %) compared with UGModel (sen 57.7 %, spe 76.4 %) and pQPGModel (sen 63.4 %, spe 81.8 %). ConclusionRG PET/CT performs better in the quantitative assessment of metabolic heterogeneity for lung lesions and the subsequent diagnosis in patients with NSCLC compared with UG PET/CT.

Motion-induced dose perturbations in photon radiotherapy and proton therapy measured by deformable liver-shaped 3D dosimeters in an anthropomorphic phantom

Background and purposeThe impact of intrafractional motion and deformations on clinical radiotherapy delivery has so far only been investigated by simulations as well as point and planar dose measurements. The aim of this study was to combine anthropomorphic 3D dosimetry with a deformable abdominal phantom to measure the influence of intra-fractional motion and gating in photon radiotherapy and evaluate the applicability in proton therapy. Material and methodsAn abdominal phantom was modified to hold a deformable anthropomorphic 3D dosimeter shaped as a human liver. A liver-specific photon radiotherapy and a proton pencil beam scanning therapy plan were delivered to the phantom without motion as well as with 12 mm sinusoidal motion while using either no respiratory gating or respiratory gating. ResultsUsing the stationary irradiation as reference the local 3 %/2 mm 3D gamma index pass rate of the motion experiments in the planning target volume (PTV) was above 97 % (photon) and 78 % (proton) with gating whereas it was below 74 % (photon) and 45 % (proton) without gating. ConclusionsFor the first time a high-resolution deformable anthropomorphic 3D dosimeter embedded in a deformable abdominal phantom was applied for experimental validation of both photon and proton treatments of targets exhibiting respiratory motion. It was experimentally shown that gating improves dose coverage and the geometrical accuracy for both photon radiotherapy and proton therapy.

Evaluating Danish Breast Cancer Group locoregional radiotherapy guideline adherence in clinical treatment data 2008–2016: The DBCG RT Nation study

Background and purposeGuideline adherence in radiotherapy is crucial for maintaining treatment quality and consistency, particularly in non-trial patient settings where most treatments occur. The study aimed to assess the impact of guideline changes on treatment planning practices and compare manual registry data accuracy with treatment planning data. Materials and methodsThis study utilised the DBCG RT Nation cohort, a collection of breast cancer radiotherapy data in Denmark, to evaluate adherence to guidelines from 2008 to 2016. The cohort included 7448 high-risk breast cancer patients. National guideline changes included, fractionation, introduction of respiratory gating, irradiation of the internal mammary lymph nodes, use of the simultaneous integrated boost technique and inclusion of the Left Anterior Descending coronary artery in delineation practice. Methods for structure name mapping, laterality detection, detection of temporal changes in population mean lung volume, and dose evaluation were presented and applied. Manually registered treatment characteristic data was obtained from the Danish Breast Cancer Database for comparison. ResultsThe study found immediate and consistent adherence to guideline changes across Danish radiotherapy centres. Treatment practices before guideline implementation were documented and showed a variation among centres. Discrepancies between manual registry data and actual treatment planning data were as high as 10% for some measures. ConclusionNational guideline changes could be detected in the routine treatment data, with a high degree of compliance and short implementation time. Data extracted from treatment planning data files provides a more accurate and detailed characterisation of treatments and guideline adherence than medical register data.