First-in-human imaging using a MR-compatible e4D ultrasound probe for motion management of radiotherapy

PurposeRespiration-induced tumor or organ positional changes can impact the accuracy of external beam radiotherapy. Motion management strategies are used to account for these changes during treatment. The authors report on the development, testing, and first-in-human evaluation of an electronic 4D (e4D) MR-compatible ultrasound probe that was designed for hands-free operation in a MR and linear accelerator (LINAC) environment.MethodsUltrasound components were evaluated for MR compatibility. Electromagnetic interference (EMI) shielding was used to enclose the entire probe and a factory-fabricated cable shielded with copper braids was integrated into the probe. A series of simultaneous ultrasound and MR scans were acquired and analyzed in five healthy volunteers.ResultsThe ultrasound probe led to minor susceptibility artifacts in the MR images immediately proximal to the ultrasound probe at a depth of <10 mm. Ultrasound and MR-based motion traces that were derived by tracking the salient motion of endogenous target structures in the superior-inferior (SI) direction demonstrated good concordance (Pearson correlation coefficients of 0.95–0.98) between the ultrasound and MRI datasets.ConclusionWe have demonstrated that our hands-free, e4D probe can acquire ultrasound images during a MR acquisition at frame rates of approximately 4 frames per second (fps) without impacting either the MR or ultrasound image quality. This use of this technology for interventional procedures (e.g. biopsies and drug delivery) and motion compensation during imaging are also being explored.     

SBRT targets that move with respiration

The technology of treating SBRT targets that move with respiration has undergone profound changes over the last 20 years. This review article summarizes modern image guidance to localize the target in real-time to account for intra-fraction motion. The state-of-the art respiratory motion compensation techniques will be discussed, including the determination and application of appropriate margins. This includes compression, gating and breath-hold, including the use of audiovisual feedback to manage motion. Approaches to real-time tracking include the use of hybrid external-internal imaging to build a skin-to-tumor correlation, which can then be tracked with a mobile robot (CyberKnife Synchrony, clinical since 2003) as well as the use of non-ionizing electromagnetic tumor surrogate localization followed by real-time tracking with a moving MLC (in clinical trials in Europe and Australia). Lastly, the clinical application of real-time MRI soft-tissue imaging to deliver adaptive, iso-toxic treatments will be presented.     

Immobilization for carbon ion beam ablation of cardiac structures in a porcine model

IntroductionWhereas hadron therapy of static targets is clinically established, treatment of moving organs remains a challenge. One strategy is to minimize motion of surrounding tissue mechanically and to mitigate residual motion with an appropriate irradiation technique. In this technical note, we present and characterize such an immobilization technique for a novel noncancerous application: the irradiation of small targets in hearts with scanned carbon ion beams in a porcine model for elimination of arrhythmias.Material and methodsA device for immobilization was custom-built. Both for the treatment planning 4D-CT scan and for irradiation, breath-hold at end-exhale was enforced using a remotely-controlled respirator. Target motion was thus reduced to heartbeat only. Positioning was verified by orthogonal X-rays followed by couch shift if necessary. Reproducibility of bony anatomy, diaphragm, and heart position after repositioning and between repeated breath-hold maneuvers was evaluated on X-rays and cardiac-gated 4D-CTs. Treatment was post hoc simulated on sequential 4D-CTs for a subset of animals, after immediate repositioning and after a delay of one week, similar to the delay between imaging and irradiation.ResultsBreath-hold without repositioning was highly reproducible with an RMS deviation of at most one millimeter. 4D-CTs showed larger deformations in soft tissue, but treatment simulation on sequential images resulted in full target coverage (V95 >95%).ConclusionThe method of immobilization permitted reproducible positioning of mobile, thoracic targets for range-sensitive particle therapy. The presented immobilization strategy could be a reasonable approach for future animal investigations with the ultimate goal of translation to therapy in men.     

多切面法联合彩色多普勒超声在胎儿先天性心脏病诊断中的应用

目的:探讨多切面法联合彩色多普勒超声在胎儿先天性心脏病(congenital heart diseases,CHD)诊断中的应用价值。方法:采用多切面法联合彩色多普勒超声对2015年5月~2016年7月300例胎儿进行CHD筛查,并与随访的产后超声或尸解结果作对照。结果:300例胎儿经产前超声联合多切面法检出CHD胎儿20例,检出率为6.7%,经产后超声或尸解确诊14例:三尖瓣下移畸形1例,室间隔完整型完全性大动脉转位1例,完全性房室间隔缺损1例,室间隔完整型肺动脉瓣闭锁1例,双流入型单心室1例,共同动脉干Ⅰ型2例,单纯室间隔缺损2例,法洛氏四联症2例,主动脉弓缩窄1例,肺动脉瓣轻度狭窄1例,二尖瓣闭锁并共同动脉干1例;误诊为单纯室间隔缺损1例,误诊为法洛氏四联症1例,病例流失4例。产前超声联合多切面法对有、无高危因素的检出率分别为3.79%、13.48%,比较有统计学意义(P0.05)。产前超声联合多切面法诊断CHD的灵敏度为100%、特异度为99.66%、阳性预测值为80.00%、阴性预测值为100%。结论:多切面法联合彩色多普勒超声在胎儿CHD诊断中具有较高的应用价值。     

Ultrasound tracking for intra-fractional motion compensation in radiation therapy

Modern techniques as ion beam therapy or 4D imaging require precise target position information. However, target motion particularly in the abdomen due to respiration or patient movement is still a challenge and demands methods that detect and compensate this motion. Ultrasound represents a non-invasive, dose-free and model-independent alternative to fluoroscopy, respiration belt or optical tracking of the patient surface. Thus, ultrasound based motion tracking was integrated into irradiation with actively scanned heavy ions. In a first in vitro experiment, the ultrasound tracking system was used to compensate diverse sinusoidal target motions in two dimensions. A time delay of ∼200 ms between target motion and reported position data was compensated by a prediction algorithm (artificial neural network). The irradiated films proved feasibility of the proposed method. Furthermore, a practicable and reliable calibration workflow was developed to enable the transformation of ultrasound tracking data to the coordinates of the treatment delivery or imaging system – even if the ultrasound probe moves due to respiration. A first proof of principle experiment was performed during time-resolved positron emission tomography (4DPET) to test the calibration workflow and to show the accuracy of an ultrasound based motion tracking in vitro. The results showed that optical ultrasound tracking can reach acceptable accuracies and encourage further research.     

Robustness of post-reconstruction and direct kinetic parameter estimates under rigid head motion in dynamic brain PET imaging

ObjectiveDynamic PET imaging is extensively used in brain imaging to estimate parametric maps. Inter-frame motion can substantially disrupt the voxel-wise time-activity curves (TACs), leading to erroneous maps during kinetic modelling. Therefore, it is important to characterize the robustness of kinetic parameters under various motion and kinetic model related factors.MethodsFully 4D brain simulations ([¹⁵O]H₂O and [¹⁸F]FDG dynamic datasets) were performed using a variety of clinically observed motion patterns. Increasing levels of head motion were investigated as well as varying temporal frames of motion initiation. Kinetic parameter estimation was performed using both post-reconstruction kinetic analysis and direct 4D image reconstruction to assess bias from inter-frame emission blurring and emission/attenuation mismatch.ResultsKinetic parameter bias heavily depends on the time point of motion initiation. Motion initiated towards the end of the scan results in the most biased parameters. For the [¹⁸F]FDG data, k₄ is the more sensitive parameter to positional changes, while K₁ and blood volume were proven to be relatively robust to motion. Direct 4D image reconstruction appeared more sensitive to changes in TACs due to motion, with parameter bias spatially propagating and depending on the level of motion.ConclusionKinetic parameter bias highly depends upon the time frame at which motion occurred, with late frame motion-induced TAC discontinuities resulting in the least accurate parameters. This is of importance during prolonged data acquisition as is often the case in neuro-receptor imaging studies. In the absence of a motion correction, use of TOF information within 4D image reconstruction could limit the error propagation.     

Measurement and Correction of Microscopic Head Motion during Magnetic Resonance Imaging of the Brain

Magnetic resonance imaging (MRI) is a widely used method for non-invasive study of the structure and function of the human brain. Increasing magnetic field strengths enable higher resolution imaging; however, long scan times and high motion sensitivity mean that image quality is often limited by the involuntary motion of the subject. Prospective motion correction is a technique that addresses this problem by tracking head motion and continuously updating the imaging pulse sequence, locking the imaging volume position and orientation relative to the moving brain. The accuracy and precision of current MR-compatible tracking systems and navigator methods allows the quantification and correction of large-scale motion, but not the correction of very small involuntary movements in six degrees of freedom. In this work, we present an MR-compatible tracking system comprising a single camera and a single 15 mm marker that provides tracking precision in the order of 10 m and 0.01 degrees. We show preliminary results, which indicate that when used for prospective motion correction, the system enables improvement in image quality at both 3 T and 7 T, even in experienced and cooperative subjects trained to remain motionless during imaging. We also report direct observation and quantification of the mechanical ballistocardiogram (BCG) during simultaneous MR imaging. This is particularly apparent in the head-feet direction, with a peak-to-peak displacement of 140 m.     

Experimental verification of a two-dimensional respiratory motion compensation system with ultrasound tracking technique in radiation therapy

This study proposed respiratory motion compensation system (RMCS) combined with an ultrasound image tracking algorithm (UITA) to compensate for respiration-induced tumor motion during radiotherapy, and to address the problem of inaccurate radiation dose delivery caused by respiratory movement.This study used an ultrasound imaging system to monitor respiratory movements combined with the proposed UITA and RMCS for tracking and compensation of the respiratory motion. Respiratory motion compensation was performed using prerecorded human respiratory motion signals and also sinusoidal signals. A linear accelerator was used to deliver radiation doses to GAFchromic EBT3 dosimetry film, and the conformity index (CI), root-mean-square error, compensation rate (CR), and planning target volume (PTV) were used to evaluate the tracking and compensation performance of the proposed system.Human respiratory pattern signals were captured using the UITA and compensated by the RMCS, which yielded CR values of 34–78%. In addition, the maximum coronal area of the PTV ranged from 85.53 mm² to 351.11 mm² (uncompensated), which reduced to from 17.72 mm² to 66.17 mm² after compensation, with an area reduction ratio of up to 90%. In real-time monitoring of the respiration compensation state, the CI values for 85% and 90% isodose areas increased to 0.7 and 0.68, respectively.The proposed UITA and RMCS can reduce the movement of the tracked target relative to the LINAC in radiation therapy, thereby reducing the required size of the PTV margin and increasing the effect of the radiation dose received by the treatment target.     

Introduction to rodent cardiac imaging

Imaging is a noninvasive complement to traditional methods (such as histology) in rodent cardiac studies. Assessments of structure and function are possible with ultrasound, microcomputed tomography (microCT), and magnetic resonance (MR) imaging. Cardiac imaging in the rodent poses a challenge because of the size of the animal and its rapid heart rate. Each aspect in the process of rodent cardiac imaging-animal preparation, choice of anesthetic, selection of gating method, image acquisition, and image interpretation and measurement-requires careful consideration to optimize image quality and to ensure accurate and reproducible data collection. Factors in animal preparation that can affect cardiac imaging are the choice of anesthesia regime (injected or inhaled), intubated or free-breathing animals, physiological monitoring (ECG, respiration, and temperature), and animal restraint. Each will vary depending on the method of imaging and the length of the study. Gating strategies, prospective or retrospective, reduce physiological motion artifacts and isolate specific time points in the cardiac cycle (i.e., end-diastole and end-systole) where measurements are taken. This article includes a simple explanation of the physics of ultrasound, microCT, and MR to describe how images are generated. Subsequent sections provide reviews of animal preparation, image acquisition, and measurement techniques in each modality specific to assessing cardiac functions such as ejection fraction, fractional shortening, stroke volume, cardiac output, and left ventricular mass. The discussion also includes the advantages and disadvantages of the different imaging modalities. With the use of ultrasound, microCT, and MR, it is possible to create 2-, 3-, and 4-dimensional views to characterize the structure and function of the rodent heart.     

Interpolated Compressed Sensing for 2D Multiple Slice Fast MR Imaging

Sparse MRI has been introduced to reduce the acquisition time and raw data size by undersampling the k-space data. However, the image quality, particularly the contrast to noise ratio (CNR), decreases with the undersampling rate. In this work, we proposed an interpolated Compressed Sensing (iCS) method to further enhance the imaging speed or reduce data size without significant sacrifice of image quality and CNR for multi-slice two-dimensional sparse MR imaging in humans. This method utilizes the k-space data of the neighboring slice in the multi-slice acquisition. The missing k-space data of a highly undersampled slice are estimated by using the raw data of its neighboring slice multiplied by a weighting function generated from low resolution full k-space reference images. In-vivo MR imaging in human feet has been used to investigate the feasibility and the performance of the proposed iCS method. The results show that by using the proposed iCS reconstruction method, the average image error can be reduced and the average CNR can be improved, compared with the conventional sparse MRI reconstruction at the same undersampling rate.     

Towards Active Tracking of Beating Heart Motion in the Presence of Arrhythmia for Robotic Assisted Beating Heart Surgery

In robotic assisted beating heart surgery, the control architecture for heart motion tracking has stringent requirements in terms of bandwidth of the motion that needs to be tracked. In order to achieve sufficient tracking accuracy, feed-forward control algorithms, which rely on estimations of upcoming heart motion, have been proposed in the literature. However, performance of these feed-forward motion control algorithms under heart rhythm variations is an important concern. In their past work, the authors have demonstrated the effectiveness of a receding horizon model predictive control-based algorithm, which used generalized adaptive predictors, under constant and slowly varying heart rate conditions. This paper extends these studies to the case when the heart motion statistics change abruptly and significantly, such as during arrhythmias. A feasibility study is carried out to assess the motion tracking capabilities of the adaptive algorithms in the occurrence of arrhythmia during beating heart surgery. Specifically, the tracking performance of the algorithms is evaluated on prerecorded motion data, which is collected in vivo and includes heart rhythm irregularities. The algorithms are tested using both simulations and bench experiments on a three degree-of-freedom robotic test bed. They are also compared with a position-plus-derivative controller as well as a receding horizon model predictive controller that employs an extended Kalman filter algorithm for predicting future heart motion.     

Influence of Thin Slice Reconstruction on CT Brain Perfusion Analysis

Objectives

Although CT scanners generally allow dynamic acquisition of thin slices (1 mm), thick slice (≥5 mm) reconstruction is commonly used for stroke imaging to reduce data, processing time, and noise level. Thin slice CT perfusion (CTP) reconstruction may suffer less from partial volume effects, and thus yield more accurate quantitative results with increased resolution. Before thin slice protocols are to be introduced clinically, it needs to be ensured that this does not affect overall CTP constancy. We studied the influence of thin slice reconstruction on average perfusion values by comparing it with standard thick slice reconstruction.

Materials and Methods

From 50 patient studies, absolute and relative hemisphere averaged estimates of cerebral blood volume (CBV), cerebral blood flow (CBF), mean transit time (MTT), and permeability-surface area product (PS) were analyzed using 0.8, 2.4, 4.8, and 9.6 mm slice reconstructions. Specifically, the influence of Gaussian and bilateral filtering, the arterial input function (AIF), and motion correction on the perfusion values was investigated.

Results

Bilateral filtering gave noise levels comparable to isotropic Gaussian filtering, with less partial volume effects. Absolute CBF, CBV and PS were 22%, 14% and 46% lower with 0.8 mm than with 4.8 mm slices. If the AIF and motion correction were based on thin slices prior to reconstruction of thicker slices, these differences reduced to 3%, 4% and 3%. The effect of slice thickness on relative values was very small.

Conclusions

This study shows that thin slice reconstruction for CTP with unaltered acquisition protocol gives relative perfusion values without clinically relevant bias. It does however affect absolute perfusion values, of which CBF and CBV are most sensitive. Partial volume effects in large arteries and veins lead to overestimation of these values. The effects of reconstruction slice thickness should be taken into account when absolute perfusion values are used for clinical decision making.     

The feasibility of an approximate irregular field dose distribution simulation program applied to a respiratory motion compensation system

PurposeThis study optimized our previously proposed simulation program for the approximate irregular field dose distribution (SPAD) and applied it to a respiratory motion compensation system (RMCS) and respiratory motion simulation system (RMSS). The main purpose was to rapidly analyze the two-dimensional dose distribution and evaluate the compensation effect of the RMCS during radiotherapy.MethodsThis study modified the SPAD to improve the rapid analysis of the dose distribution. In the experimental setup, four different respiratory signal patterns were input to the RMSS for actuation, and an ultrasound image tracking algorithm was used to capture the real-time respiratory displacement, which was input to the RMCS for actuation. A linear accelerator simultaneously irradiated the EBT3 film. The gamma passing rate was used to verify the dose similarity between the EBT3 film and the SPAD, and conformity index (CI) and compensation rate (CR) were used to quantify the compensation effect.ResultsThe Gamma passing rates were 70.48–81.39% (2%/2mm) and 88.23–96.23% (5%/3mm) for various collimator opening patterns. However, the passing rates of the SPAD and EBT3 film ranged from 61.85% to 99.85% at each treatment time point. Under the four different respiratory signal patterns, CR ranged between 21% and 75%. After compensation, the CI for 85%, 90%, and 95% isodose constraints were 0.78, 0.57, and 0.12, respectively.ConclusionsThis study has demonstrated that the dose change during each stage of the treatment process can be analyzed rapidly using the improved SPAD. After compensation, applying the RMCS can reduce the treatment errors caused by respiratory movements.     

A three dimensional drive system for use with fillable emission phantoms for SPECT and PET imaging

Respiratory motion artefacts pose significant challenges for imaging of the lung and thorax. Dynamic phantoms have previously been applied to the study of respiratory motion, however, most moving platforms have been capable of movement in either one or two dimensions only. We describe a moving platform suitable for SPECT-CT and PET-CT imaging. The platform allows a fillable emission phantom to simulate rigid motion in three dimensions. Elliptical periodical motion of 1.5 cm in all three orthogonal planes was simulated using a series of cams moving a baseplate up and across a slope of 45°. The frequency of movement can be varied manually between 5 and 25 cycles per minute in a known calibrated and reproducible manner (This encompasses the range of physiological respiratory motion). Preliminary studies demonstrated that the phantom can be used to identify motion parameters and for the qualitative assessment of motion blurring in reconstructed images.     

冠状动脉磁共振血管成像和CT对可疑冠心病患者心脏事件的预测价值的比较研究

摘要 目的：探讨与比较冠状动脉核磁共振(MR)血管成像和CT对可疑冠心病患者心脏事件的预测价值。方法：2018年4月到2020年10月选择在本院诊治的103例可疑冠心病患者作为研究对象,所有患者都给予冠状动脉MRI血管成像与64层螺旋CT冠状动脉成像检查,记录影像学特征。随访患者的预后并进行预测价值分析。结果：103例可疑冠心病患者随访到2021年4月1日,发生心血管不良终点事件23例(不良事件组),发生率为22.3%。不良事件组的MRI血管成像显示右冠状动脉血管长度与内径都低于非不良事件组(P<0.05)。不良事件组的CT显示斑块率、斑块性质等与非不良事件组对比差异有统计学意义(P<0.05),两组斑块位置对比差异无统计学意义(P>0.05)。多因素Cox回归分析显示斑块性质、斑块率、右冠状动脉血管长度与内径都为导致心血管不良终点事件的重要因素(P<0.05)。结论：冠状动脉MRI血管成像和CT都可有效预测可疑冠心病患者心脏事件发生情况,能满足临床诊断可疑冠心病与预测预后的要求。     

Abdominal magnetic resonance imaging in small rodents using a clinical 1.5 T MR scanner

Because of superior soft-tissue contrast compared to other imaging techniques, non-invasive abdominal magnetic resonance imaging (MRI) is ideal for monitoring organ regeneration, tissue repair, cancer stage, and treatment effects in a wide variety of experimental animal models. Currently, sophisticated MR protocols, including technically demanding procedures for motion artefact compensation, achieve an MRI resolution limit of < 100 microm under ideal conditions. However, such a high spatial resolution is not required for most experimental rodent studies. This article describes both a detailed imaging protocol for MR data acquisition in a ubiquitously and commercially available 1.5 T MR unit and 3-dimensional volumetry of organs, tissue components, or tumors. Future developments in MR technology will allow in vivo investigation of physiological and pathological processes at the cellular and even the molecular levels. Experimental MRI is crucial for non-invasive monitoring of a broad range of biological processes and will further our general understanding of physiology and disease.     

Whole Heart Coronary Imaging with Flexible Acquisition Window and Trigger Delay

Coronary magnetic resonance imaging (MRI) requires a correctly timed trigger delay derived from a scout cine scan to synchronize k-space acquisition with the quiescent period of the cardiac cycle. However, heart rate changes between breath-held cine and free-breathing coronary imaging may result in inaccurate timing errors. Additionally, the determined trigger delay may not reflect the period of minimal motion for both left and right coronary arteries or different segments. In this work, we present a whole-heart coronary imaging approach that allows flexible selection of the trigger delay timings by performing k-space sampling over an enlarged acquisition window. Our approach addresses coronary motion in an interactive manner by allowing the operator to determine the temporal window with minimal cardiac motion for each artery region. An electrocardiogram-gated, k-space segmented 3D radial stack-of-stars sequence that employs a custom rotation angle is developed. An interactive reconstruction and visualization platform is then employed to determine the subset of the enlarged acquisition window for minimal coronary motion. Coronary MRI was acquired on eight healthy subjects (5 male, mean age = 37 ± 18 years), where an enlarged acquisition window of 166–220 ms was set 50 ms prior to the scout-derived trigger delay. Coronary visualization and sharpness scores were compared between the standard 120 ms window set at the trigger delay, and those reconstructed using a manually adjusted window. The proposed method using manual adjustment was able to recover delineation of five mid and distal right coronary artery regions that were otherwise not visible from the standard window, and the sharpness scores improved in all coronary regions using the proposed method. This paper demonstrates the feasibility of a whole-heart coronary imaging approach that allows interactive selection of any subset of the enlarged acquisition window for a tailored reconstruction for each branch region.     

Deformation of the human brain induced by mild angular head acceleration

Deformation of the human brain was measured in tagged magnetic resonance images (MRI) obtained dynamically during angular acceleration of the head. This study was undertaken to provide quantitative experimental data to illuminate the mechanics of traumatic brain injury (TBI). Mild angular acceleration was imparted to the skull of a human volunteer inside an MR scanner, using a custom MR-compatible device to constrain motion. A grid of MR "tag" lines was applied to the MR images via spatial modulation of magnetization (SPAMM) in a fast gradient echo imaging sequence. Images of the moving brain were obtained dynamically by synchronizing the imaging process with the motion of the head. Deformation of the brain was characterized quantitatively via Lagrangian strain. Consistent patterns of radial-circumferential shear strain occur in the brain, similar to those observed in models of a viscoelastic gel cylinder subjected to angular acceleration. Strain fields in the brain, however, are clearly mediated by the effects of heterogeneity, divisions between regions of the brain (such as the central fissure and central sulcus) and the brain's tethering and suspension system, including the dura mater, falx cerebri, and tentorium membranes.     

Spatial and Temporal Control of Hyperthermia Using Real Time Ultrasonic Thermal Strain Imaging with Motion Compensation,Phantom Study

Mild hyperthermia has been successfully employed to induce reversible physiological changes that can directly treat cancer and enhance local drug delivery. In this approach, temperature monitoring is essential to avoid undesirable biological effects that result from thermal damage. For thermal therapies, Magnetic Resonance Imaging (MRI) has been employed to control real-time Focused Ultrasound (FUS) therapies. However, combined ultrasound imaging and therapy systems offer the benefits of simple, low-cost devices that can be broadly applied. To facilitate such technology, ultrasound thermometry has potential to reliably monitor temperature. Control of mild hyperthermia was previously achieved using a proportional-integral-derivative (PID) controller based on thermocouple measurements. Despite accurate temporal control of heating, this method is limited by the single position at which the temperature is measured. Ultrasound thermometry techniques based on exploiting the thermal dependence of acoustic parameters (such as longitudinal velocity) can be extended to create thermal maps and allow an accurate monitoring of temperature with good spatial resolution. However, in vivo applications of this technique have not been fully developed due to the high sensitivity to tissue motion. Here, we propose a motion compensation method based on the acquisition of multiple reference frames prior to treatment. The technique was tested in the presence of 2-D and 3-D physiological-scale motion and was found to provide effective real-time temperature monitoring. PID control of mild hyperthermia in presence of motion was then tested with ultrasound thermometry as feedback and temperature was maintained within 0.3°C of the requested value.     

Quantization accuracy of short-duration respiratory-gated PET/CT acquisitions

PurposePET/CT acquisitions are affected by physiological motion, which lowers the quantization accuracy. Respiratory-gated PET/CT methods require a long acquisition time, which may not be compatible with the clinical schedule. The objective of the present study was to assess the quantization accuracy of short-duration, respiratory-gated PET acquisitions and processing with the “CT-based” methodology developed in our laboratory.MethodsQuantization accuracy was first assessed in a phantom study. A standard (“Ungated”) PET/CT acquisition was followed by a 10-minute list-mode acquisition with simultaneous respiratory signal recording and a short breath-hold CT scan (BH-CT). These acquisitions were repeated 10 times. For the CT-based images, we reconstructed (i) 10 full-duration (FD-CT-based) volumes that took account of all events recorded in the position defined by BH-CT and (ii) 10 short-duration (SD-CT-based) volumes based on only 30 seconds of selected events. Using these volumes, we performed a bias–variance analysis to assess the effects of respiration-motion reduction and the counting statistics on the quantization accuracy. We also applied Ungated, FD- and SD-CT-based methods to 16 patients (21 pulmonary lesions) and measured the maximum standardized uptake (SUVmax) values.ResultsThe bias values were 71%, 40% and 44% for Ungated, FD- and SD-CT-based images, respectively. In the clinical study, there was a statistically significant difference in SUVmax between Ungated images and both the CT-Based images (p < 0.02) but not between the FD-CT-Based and SD-CT-Based images (p = 0.42).ConclusionOur findings demonstrated that the additional acquisition time required by the CT-based method can be reduced without altering quantitative accuracy.