[Gene diagnosis of four patients with protein C deficiency]

目的

探讨蛋白C缺陷症的分子发病机制。

方法

对4例蛋白C缺陷症患者进行常规诊断和基因分析。

结果

①例1，女，40岁。临床诊断：左下肢深静脉血栓形成。蛋白C活性（PC∶C）48%，蛋白S活性（PS∶C）26.3%，抗凝血酶活性（AT∶C) 75.6%。基因检测结果：蛋白C基因（PROC）启动子C5156T杂合突变、2号外显子区域存在A6578T杂合突变。给予抗凝、溶栓、滤器植入等治疗，症状好转出院。②例2，女，32岁。临床诊断：双下肢深静脉血栓，双上、下肢缺血，双下肢皮肤软组织感染。PC∶C 27%，PS∶C 22.9%，AT∶C 86.7%。基因检测结果：PROC基因启动子C5156T杂合突变、A5045T杂合突变。给予抗凝、抗感染等治疗，因呼吸衰竭、感染性休克、DIC死亡。③例3，女，28岁。临床诊断：右髂静脉及股深静脉血栓。PC∶C 58%，PS∶C 57.3%，AT∶C 80.8%。基因检测结果：PROC启动子C4867T杂合突变，7号外显子12702-12704 AGA (Arg192）或12705-12707 AGA（Arg193）杂合缺失，9号外显子G15240A杂合突变。给予抗凝、溶栓、滤器植入等治疗，症状好转出院。④例4，男，30岁。临床诊断：左下肢深静脉血栓，双下肺动脉栓塞伴双下肺梗死。PC∶C 50%，PS∶C 75.0%，AT∶C 89.1%。基因检测结果：PROC启动子C4867T纯合突变、G4880A纯合突变和A5045T杂合突变，2号外显子T6589C杂合突变。给予抗凝、溶栓、滤器植入等相关治疗，症状好转出院。⑤多态性分析：PROC基因启动子C4867T杂合突变、G4880A纯合突变、C5156T杂合突变为PROC启动子多态性位点。

结论

PROC启动子多态性位点G4880A、C4867T、C5156T，错义突变A5045T、A6578T、G15240A，缺失突变AGA12702-12704del或12705-12707del可能与蛋白C缺陷症有关。PROC启动子错义突变A5045T、A6578T、G15240A，缺失突变AGA12702-12704del或12705-12706del是国际首次报告。

Numerical observer for atherosclerotic plaque classification in spectral computed tomography

Spectral computed tomography (SCT) generates better image quality than conventional computed tomography (CT). It has overcome several limitations for imaging atherosclerotic plaque. However, the literature evaluating the performance of SCT based on objective image assessment is very limited for the task of discriminating plaques. We developed a numerical-observer method and used it to assess performance on discrimination vulnerable-plaque features and compared the performance among multienergy CT (MECT), dual-energy CT (DECT), and conventional CT methods. Our numerical observer was designed to incorporate all spectral information and comprised two-processing stages. First, each energy-window domain was preprocessed by a set of localized channelized Hotelling observers (CHO). In this step, the spectral image in each energy bin was decorrelated using localized prewhitening and matched filtering with a set of Laguerre-Gaussian channel functions. Second, the series of the intermediate scores computed from all the CHOs were integrated by a Hotelling observer with an additional prewhitening and matched filter. The overall signal-to-noise ratio (SNR) and the area under the receiver operating characteristic curve (AUC) were obtained, yielding an overall discrimination performance metric. The performance of our new observer was evaluated for the particular binary classification task of differentiating between alternative plaque characterizations in carotid arteries. A clinically realistic model of signal variability was also included in our simulation of the discrimination tasks. The inclusion of signal variation is a key to applying the proposed observer method to spectral CT data. Hence, the task-based approaches based on the signal-known-exactly/background-known-exactly (SKE/BKE) framework and the clinical-relevant signal-known-statistically/background-known-exactly (SKS/BKE) framework were applied for analytical computation of figures of merit (FOM). Simulated data of a carotid-atherosclerosis patient were used to validate our methods. We used an extended cardiac-torso anthropomorphic digital phantom and three simulated plaque types (i.e., calcified plaque, fatty-mixed plaque, and iodine-mixed blood). The images were reconstructed using a standard filtered backprojection (FBP) algorithm for all the acquisition methods and were applied to perform two different discrimination tasks of: (1) calcified plaque versus fatty-mixed plaque and (2) calcified plaque versus iodine-mixed blood. MECT outperformed DECT and conventional CT systems for all cases of the SKE/BKE and SKS/BKE tasks (all [Formula: see text]). On average of signal variability, MECT yielded the SNR improvements over other acquisition methods in the range of 46.8% to 65.3% (all [Formula: see text]) for FBP-Ramp images and 53.2% to 67.7% (all [Formula: see text]) for FBP-Hanning images for both identification tasks. This proposed numerical observer combined with our signal variability framework is promising for assessing material characterization obtained through the additional energy-dependent attenuation information of SCT. These methods can be further extended to other clinical tasks such as kidney or urinary stone identification applications.

Impact of pedicle-lengthening osteotomy on spinal canal volume and neural foramen size in three types of lumbar spinal stenosis

Objectives

Pedicle-lengthening osteotomy is a novel surgery for lumbar spinal stenosis (LSS), which achieves substantial enlargement of the spinal canal by expansion of the bilateral pedicle osteotomy sites. Few studies have evaluated the impact of this new surgery on spinal canal volume (SCV) and neural foramen dimension (NFD) in three different types of LSS patients.

Methods

CT scans were performed on 36 LSS patients (12 central canal stenosis (CCS), 12 lateral recess stenosis (LRS), and 12 foraminal stenosis (FS)) at L4-L5, and on 12 normal (control) subjects. Mimics 14.01 workstation was used to reconstruct 3D models of the L4-L5 vertebrae and discs. SCV and NFD were measured after 1 mm, 2 mm, 3 mm, 4 mm, or 5 mm pedicle-lengthening osteotomies at L4 and/or L5. One-way analysis of variance was used to examine between-group differences.

Results

In the intact state, SVC and NFD were significantly larger in the control group compared with the LSS groups (P<0.05). After lengthening at L4, the percentage increase in SCV (per millimetre) was LRS>CCS>FS>Control. After lengthening at L5 and L4-L5, the percentage increase in SCV (per millimetre) was LRS>FS>CCS>Control. After lengthening at L4 and L4-L5, the percentage increase in NFD (per millimetre) was FS>CCS>LRS>Control. After lengthening at L5, the percentage increase in NFD (per millimetre) was CCS>LRS>control>FS.

Conclusions

LRS patients are the most suitable candidates for treatment with pedicle-lengthening osteotomy. Lengthening L4 pedicles produced larger percentage increases in NFD than lengthening L5 pedicles (p < 0.05). Lengthening L4 pedicles may be the most effective option for relieving foraminal compression in LSS patients.

Cite this article: P. Li, L. Qian, W. D. Wu, C. F. Wu, J. Ouyang. Impact of pedicle-lengthening osteotomy on spinal canal volume and neural foramen size in three types of lumbar spinal stenosis. Bone Joint Res 2016;5:239–246. DOI: 10.1302/2046-3758.56.2000469.

Investigation of cone-beam CT image quality trade-off for image-guided radiation therapy

It is well-known that projections acquired over an angular range slightly over 180° (so-called short scan) are sufficient for fan-beam reconstruction. However, due to practical imaging conditions (projection data and reconstruction image discretization, physical factors, and data noise), the short-scan reconstructions may have different appearances and properties from the full-scan (scans over 360°) reconstructions. Nevertheless, short-scan configurations have been used in applications such as cone-beam CT (CBCT) for head-neck-cancer image-guided radiation therapy (IGRT) that only requires a small field of view due to the potential reduced imaging time and dose. In this work, we studied the image quality trade-off for full, short, and full/short scan configurations with both conventional filtered-backprojection (FBP) reconstruction and iterative reconstruction algorithms based on total-variation (TV) minimization for head-neck-cancer IGRT. Anthropomorphic and Catphan phantoms were scanned at different exposure levels with a clinical scanner used in IGRT. Both visualization- and numerical-metric-based evaluation studies were performed. The results indicate that the optimal exposure level and number of views are in the middle range for both FBP and TV-based iterative algorithms and the optimization is object-dependent and task-dependent. The optimal view numbers decrease with the total exposure levels for both FBP and TV-based algorithms. The results also indicate there are slight differences between FBP and TV-based iterative algorithms for the image quality trade-off: FBP seems to be more in favor of larger number of views while the TV-based algorithm is more robust to different data conditions (number of views and exposure levels) than the FBP algorithm. The studies can provide a general guideline for image-quality optimization for CBCT used in IGRT and other applications.

Quercetin is an effective inhibitor of quorum sensing, biofilm formation and virulence factors in Pseudomonas aeruginosa

AIMS

The study aimed to perform a systematic investigation of the effects of quercetin on biofilm formation and virulence factors in Pseudomonas aeruginosa.

METHODS AND RESULTS

The Ps. aeruginosa strain PAO1 was selected as the test strain. The results indicated that quercetin did not impact the growth of PAO1 as determined by MIC and growth curve analysis. However, this compound significantly inhibited (P < 0·05) biofilm formation and production of virulence factors including pyocyanin, protease and elastase at a lower concentration than those for most previously reported plant extracts and substances. Considering the central role of quorum sensing (QS) in the regulation of biofilm and virulence factor, we further detected the transcriptional changes associated with QS and found that the expression levels of lasI, lasR, rhlI and rhlR were significantly reduced (P < 0·05) by 34, 68, 57 and 50%, respectively, in response to 16 μg ml(-1) quercetin.

CONCLUSIONS

This study indicated that quercetin is an effective inhibitor of biofilm formation and virulence factors in Ps. aeruginosa.

SIGNIFICANCE AND IMPACT OF THE STUDY

This is the first study to demonstrate that quercetin is an effective inhibitor of QS, biofilm formation and virulence factors in Ps. aeruginosa. Furthermore, quercetin might have potential in fighting biofilm-related infections.

Restoration of the spinal canal volume in stenosis dependent on pedicle-lengthening distance in pedicle-lengthening osteotomy: A three dimensional simulation

AIMS

This study aimed to determine the relationship between pedicle-lengthening distance and bulge-canal volume ratio in cases of lumbar spinal stenosis, to provide a theoretical basis for the extent of lengthening in pedicle-lengthening osteotomies.

METHODS

Three-dimensional reconstructions of CT images were performed for 69 patients (33 men and 36 women) (mean age 49.96 years; 24 to 81). Simulated pedicle-lengthening osteotomies and disc bulge and spinal canal volume calculations were performed using Mimics software.

RESULTS

The mean spinal canal volume of the two groups, L4 and L5, were 14 646.81 mm(3) (5918.60 to 22 717.77) and 16 408.47 mm(3) (8678.21 to 31 204.79), respectively. The mean lengthening distance was 2.17 mm (0.5 to 4.8) and the mean bulge-canal volume ratio was 0.23 (0.05 to 0.48). The pedicle-lengthening distance of the two groups were very strongly correlated with disc bulge volume and bulge-canal volume ratio (p < 0.001); the predictive equation was established as L = 0.06 + 9.06R (where L equals the pedicle-lengthening distance and R represents the bulge-canal volume ratio).

DISCUSSION

Our findings indicated that lumbar pedicle-lengthening distance strongly correlates with bulge-canal volume ratio, which can be estimated before surgery from CT images.

TAKE HOME MESSAGE

The predictive equation could help surgeons to decide the pedicle lengthening distance according to individual's condition and guide the surgery effectively.

Evaluation of Immune Profiles and MicroRNA Expression Profiles in Peripheral Blood Mononuclear Cells of Long-Term Stable Liver Transplant Recipients and Recipients With Acute Rejection Episodes

OBJECTIVE

This study aimed to document the difference of immunophenotypes in peripheral blood mononuclear cells (PBMCs) between long-term stable liver transplant recipients and recipients with acute rejection. We also sought to identify whether there is any correlation between microRNA (miRNA) expression profile and the differential immunoprofile in these 2 groups to establish a specific miRNA biomarker to identify potential liver transplant recipients.

METHODS

PBMCs were isolated from 53 stable liver transplant recipients (STA group) and 15 liver transplant recipients with repeated biopsy-proven rejection episodes admitted to our hospital. Immunoprofiles were analyzed by means of flow cytometry. Analysis of miRNA expression in the PBMCs was performed by means of real-time polymerase chain reaction.

RESULTS

The immune profiling analysis showed increased frequency of peripheral natural killer cells and regulatory T cells in stable liver transplant recipients compared with the acute rejection recipients and healthy volunteers (P < .05). There was no significant difference in the immune cell levels (CD19(+) B cells, CD4(+) T cells, and CD8(+) T cells) in PBMCs among the transplant recipient groups and healthy control subjects. Three miRNAs, miR-18b, miR-340, and miR-106b, were up-regulated in the PBMCs of the STA recipients compared with recipients with acute rejection.

CONCLUSIONS

These results suggest that miR-18b, miR-340, and miR-106b, which regulate the expression of specific immunophenotypes, can be used as potential biomarkers to identify long-term stable liver transplant recipients from recipients with acute rejection.

National Electrical Manufacturers Association and Clinical Evaluation of a Novel Brain PET/CT Scanner

The aim of this study was to determine the performance of a novel mobile human brain/small-animal PET/CT system. The scanner has a 35.7-cm-diameter bore and a 22-cm axial extent. The detector ring has 7 modules each with 3 × 4 cerium-doped lutetium yttrium orthosilicate crystal blocks, each consisting of 22 × 22 outer-layer and 21 × 21 inner-layer crystals, each layer 1-cm thick. Light is collected by 12 × 12 silicon photomultipliers. The integrated CT can be used for attenuation correction and anatomic localization. The scanner was designed as a low-cost device that nevertheless produces high-quality PET images with the unique capability of battery-powered propulsion, enabling use in many settings.

METHODS

Spatial resolution, sensitivity, and noise-equivalent counting rate were measured based on the National Electrical Manufacturers Association NU2-2012 procedures. Reconstruction was done with tight energy and timing cuts-400-650 keV and 7 ns-and loose cuts-350-700 keV and 10 ns. Additional image quality measurements were made from phantom, human, and animal studies. Performance was compared with a reference scanner with comparable imaging properties.

RESULTS

The full width at half maximum transverse resolution at a 1-cm (10-cm) radius was 3.2 mm (5.2-mm radial, 3.1-mm tangential), and the axial resolution was 3.5 mm (4.0 mm). A sensitivity of 7.5 and 11.7 kcps/MBq at the center for tight and loose cuts, respectively, increased to 8.8 and 13.9 kcps/MBq, respectively, at a 10-cm radial offset. The maximum noise-equivalent counting rate of 19.5 and 22.7 kcps for tight and loose cuts, respectively, was achieved for an activity concentration of 2.9 kBq/mL. Contrast recovery for 4:1 hot cylinder to warm background was 76% for the 25-mm-diameter cylinder but decreased with decreasing cylinder size. The quantitation agreed within 2% of the known activity distribution and concentration. Brain phantom and human scans have shown agreement in SUVs and image quality with the reference scanner.

CONCLUSION

We characterized the performance of the NeuroPET/CT and showed images from the first human studies. The study shows that this scanner achieves good performance when spatial resolution, sensitivity, counting rate, and image quality along with a low cost and unique mobile capabilities are considered.

Continuous MR bone density measurement using water- and fat-suppressed projection imaging (WASPI) for PET attenuation correction in PET-MR

Due to the lack of signal from solid bone in normal MR sequences for the purpose of MR-based attenuation correction, investigators have proposed using the ultrashort echo time (UTE) pulse sequence, which yields signal from bone. However, the UTE-based segmentation approach might not fully capture the intra- and inter-subject bone density variation, which will inevitably lead to bias in reconstructed PET images. In this work, we investigated using the water- and fat-suppressed proton projection imaging (WASPI) sequence to obtain accurate and continuous attenuation for bones. This approach is capable of accounting for intra- and inter-subject bone attenuation variations. Using data acquired from a phantom, we have found that that attenuation correction based on the WASPI sequence is more accurate and precise when compared to either conventional MR attenuation correction or UTE-based segmentation approaches.

Tailored optical vector fields for ultrashort-pulse laser induced complex surface plasmon structuring

Precise tailoring of optical vector beams is demonstrated, shaping their focal electric fields and used to create complex laser micro-patterning on a metal surface. A Spatial Light Modulator (SLM) and a micro-structured S-waveplate were integrated with a picosecond laser system and employed to structure the vector fields into radial and azimuthal polarizations with and without a vortex phase wavefront as well as superposition states. Imprinting Laser Induced Periodic Surface Structures (LIPSS) elucidates the detailed vector fields around the focal region. In addition to clear azimuthal and radial plasmon surface structures, unique, variable logarithmic spiral micro-structures with a pitch Λ ∼1μm, not observed previously, were imprinted on the surface, confirming unambiguously the complex 2D focal electric fields. We show clearly also how the Orbital Angular Momentum(OAM) associated with a helical wavefront induces rotation of vector fields along the optic axis of a focusing lens and confirmed by the observed surface micro-structures.

Spectral CT using multiple balanced K-edge filters

Our goal is to validate a spectral computed tomography (CT) system design that uses a conventional X-ray source with multiple balanced K-edge filters. By performing a simultaneously synthetic reconstruction in multiple energy bins, we obtained a good agreement between measurements and model expectations for a reasonably complex phantom. We performed simulation and data acquisition on a phantom containing multiple rods of different materials using a NeuroLogica CT scanner. Five balanced K-edge filters including Molybdenum, Cerium, Dysprosium, Erbium, and Tungsten were used separately proximal to the X-ray tube. For each sinogram bin, measured filtered vector can be defined as a product of a transmission matrix, which is determined by the filters and is independent of the imaging object, and energy-binned intensity vector. The energy-binned sinograms were then obtained by inverting the transmission matrix followed by a multiplication of the filter measurement vector. For each energy bin defined by two consecutive K-edges, a synthesized energy-binned attenuation image was obtained using filtered back-projection reconstruction. The reconstructed attenuation coefficients for each rod obtained from the experiment was in good agreement with the corresponding simulated results. Furthermore, the reconstructed attenuation coefficients for a given energy bin, agreed with National Institute of Standards and Technology reference values when beam hardening within the energy bin is small. The proposed cost-effective system design using multiple balanced K-edge filters can be used to perform spectral CT imaging at clinically relevant flux rates using conventional detectors and integrating electronics.

Sparse-view spectral CT reconstruction using spectral patch-based low-rank penalty

Spectral computed tomography (CT) is a promising technique with the potential for improving lesion detection, tissue characterization, and material decomposition. In this paper, we are interested in kVp switching-based spectral CT that alternates distinct kVp X-ray transmissions during gantry rotation. This system can acquire multiple X-ray energy transmissions without additional radiation dose. However, only sparse views are generated for each spectral measurement; and the spectra themselves are limited in number. To address these limitations, we propose a penalized maximum likelihood method using spectral patch-based low-rank penalty, which exploits the self-similarity of patches that are collected at the same position in spectral images. The main advantage is that the relatively small number of materials within each patch allows us to employ the low-rank penalty that is less sensitive to intensity changes while preserving edge directions. In our optimization formulation, the cost function consists of the Poisson log-likelihood for X-ray transmission and the nonconvex patch-based low-rank penalty. Since the original cost function is difficult to minimize directly, we propose an optimization method using separable quadratic surrogate and concave convex procedure algorithms for the log-likelihood and penalty terms, which results in an alternating minimization that provides a computational advantage because each subproblem can be solved independently. We performed computer simulations and a real experiment using a kVp switching-based spectral CT with sparse-view measurements, and compared the proposed method with conventional algorithms. We confirmed that the proposed method improves spectral images both qualitatively and quantitatively. Furthermore, our GPU implementation significantly reduces the computational cost.

Accelerated acquisition of tagged MRI for cardiac motion correction in simultaneous PET-MR: phantom and patient studies

PURPOSE

Degradation of image quality caused by cardiac and respiratory motions hampers the diagnostic quality of cardiac PET. It has been shown that improved diagnostic accuracy of myocardial defect can be achieved by tagged MR (tMR) based PET motion correction using simultaneous PET-MR. However, one major hurdle for the adoption of tMR-based PET motion correction in the PET-MR routine is the long acquisition time needed for the collection of fully sampled tMR data. In this work, the authors propose an accelerated tMR acquisition strategy using parallel imaging and/or compressed sensing and assess the impact on the tMR-based motion corrected PET using phantom and patient data.

METHODS

Fully sampled tMR data were acquired simultaneously with PET list-mode data on two simultaneous PET-MR scanners for a cardiac phantom and a patient. Parallel imaging and compressed sensing were retrospectively performed by GRAPPA and kt-FOCUSS algorithms with various acceleration factors. Motion fields were estimated using nonrigid B-spline image registration from both the accelerated and fully sampled tMR images. The motion fields were incorporated into a motion corrected ordered subset expectation maximization reconstruction algorithm with motion-dependent attenuation correction.

RESULTS

Although tMR acceleration introduced image artifacts into the tMR images for both phantom and patient data, motion corrected PET images yielded similar image quality as those obtained using the fully sampled tMR images for low to moderate acceleration factors (<4). Quantitative analysis of myocardial defect contrast over ten independent noise realizations showed similar results. It was further observed that although the image quality of the motion corrected PET images deteriorates for high acceleration factors, the images were still superior to the images reconstructed without motion correction.

CONCLUSIONS

Accelerated tMR images obtained with more than 4 times acceleration can still provide relatively accurate motion fields and yield tMR-based motion corrected PET images with similar image quality as those reconstructed using fully sampled tMR data. The reduction of tMR acquisition time makes it more compatible with routine clinical cardiac PET-MR studies.

Effect of time-of-flight and point spread function modeling on detectability of myocardial defects in PET

PURPOSE

A study was designed to investigate the impact of time-of-flight (TOF) and point spread function (PSF) modeling on the detectability of myocardial defects.

METHODS

Clinical FDG-PET data were used to generate populations of defect-present and defect-absent images. Defects were incorporated at three contrast levels, and images were reconstructed by ordered subset expectation maximization (OSEM) iterative methods including ordinary Poisson, alone and with PSF, TOF, and PSF+TOF. Channelized Hotelling observer signal-to-noise ratio (SNR) was the surrogate for human observer performance.

RESULTS

For three iterations, 12 subsets, and no postreconstruction smoothing, TOF improved overall defect detection SNR by 8.6% as compared to its non-TOF counterpart for all the defect contrasts. Due to the slow convergence of PSF reconstruction, PSF yielded 4.4% less SNR than non-PSF. For reconstruction parameters (iteration number and postreconstruction smoothing kernel size) optimizing observer SNR, PSF showed larger improvement for faint defects. The combination of TOF and PSF improved mean detection SNR as compared to non-TOF and non-PSF counterparts by 3.0% and 3.2%, respectively.

CONCLUSIONS

For typical reconstruction protocol used in clinical practice, i.e., less than five iterations, TOF improved defect detectability. In contrast, PSF generally yielded less detectability. For large number of iterations, TOF+PSF yields the best observer performance.

MR-based motion correction for PET imaging using wired active MR microcoils in simultaneous PET-MR: phantom study

PURPOSE

Artifacts caused by head motion present a major challenge in brain positron emission tomography (PET) imaging. The authors investigated the feasibility of using wired active MR microcoils to track head motion and incorporate the measured rigid motion fields into iterative PET reconstruction.

METHODS

Several wired active MR microcoils and a dedicated MR coil-tracking sequence were developed. The microcoils were attached to the outer surface of an anthropomorphic(18)F-filled Hoffman phantom to mimic a brain PET scan. Complex rotation/translation motion of the phantom was induced by a balloon, which was connected to a ventilator. PET list-mode and MR tracking data were acquired simultaneously on a PET-MR scanner. The acquired dynamic PET data were reconstructed iteratively with and without motion correction. Additionally, static phantom data were acquired and used as the gold standard.

RESULTS

Motion artifacts in PET images were effectively removed by wired active MR microcoil based motion correction. Motion correction yielded an activity concentration bias ranging from -0.6% to 3.4% as compared to a bias ranging from -25.0% to 16.6% if no motion correction was applied. The contrast recovery values were improved by 37%-156% with motion correction as compared to no motion correction. The image correlation (mean ± standard deviation) between the motion corrected (uncorrected) images of 20 independent noise realizations and static reference was R(2) = 0.978 ± 0.007 (0.588 ± 0.010, respectively).

CONCLUSIONS

Wired active MR microcoil based motion correction significantly improves brain PET quantitative accuracy and image contrast.

Relative role of motion and PSF compensation in whole-body oncologic PET-MR imaging

PURPOSE

Respiratory motion and partial-volume effects are the two main sources of image degradation in whole-body PET imaging. Simultaneous PET-MR allows measurement of respiratory motion using MRI while collecting PET events. Improved PET images may be obtained by modeling respiratory motion and point spread function (PSF) within the PET iterative reconstruction process. In this study, the authors assessed the relative impact of PSF modeling and MR-based respiratory motion correction in phantoms and patient studies using a whole-body PET-MR scanner.

METHODS

An asymmetric exponential PSF model accounting for radially varying and axial detector blurring effects was obtained from point source acquisitions performed in the PET-MR scanner. A dedicated MRI acquisition protocol using single-slice steady state free-precession MR acquisitions interleaved with pencil-beam navigator echoes was developed to track respiratory motion during PET-MR studies. An iterative ordinary Poisson fully 3D OSEM PET reconstruction algorithm modeling all the physical effects of the acquisition (attenuation, scatters, random events, detectors efficiencies, PSF), as well as MR-based nonrigid respiratory deformations of tissues (in both emission and attenuation maps) was developed. Phantom and(18)F-FDG PET-MR patient studies were performed to evaluate the proposed quantitative PET-MR methods.

RESULTS

The phantom experiment results showed that PSF modeling significantly improved contrast recovery while limiting noise propagation in the reconstruction process. In patients with soft-tissue static lesions, PSF modeling improved lesion contrast by 19.7%-109%, enhancing the detectability and assessment of small tumor foci. In a patient study with small moving hepatic lesions, the proposed reconstruction technique improved lesion contrast by 54.4%-98.1% and reduced apparent lesion size by 21.8%-34.2%. Improvements were particularly important for the smallest lesion undergoing large motion at the lung-liver interface. Heterogeneous tumor structures delineation was substantially improved. Enhancements offered by PSF modeling were more important when correcting for motion at the same time.

CONCLUSIONS

The results suggest that the proposed quantitative PET-MR methods can significantly enhance the performance of tumor diagnosis and staging as compared to conventional methods. This approach may enable utilization of the full potential of the scanner in oncologic studies of both the lower abdomen, with moving lesions, as well as other parts of the body unaffected by motion.

Quantitative simultaneous positron emission tomography and magnetic resonance imaging

Simultaneous positron emission tomography and magnetic resonance imaging (PET-MR) is an innovative and promising imaging modality that is generating substantial interest in the medical imaging community, while offering many challenges and opportunities. In this study, we investigated whether MR surface coils need to be accounted for in PET attenuation correction. Furthermore, we integrated motion correction, attenuation correction, and point spread function modeling into a single PET reconstruction framework. We applied our reconstruction framework to in vivo animal and patient PET-MR studies. We have demonstrated that our approach greatly improved PET image quality.

4D numerical observer for lesion detection in respiratory-gated PET

PURPOSE

Respiratory-gated positron emission tomography (PET)/computed tomography protocols reduce lesion smearing and improve lesion detection through a synchronized acquisition of emission data. However, an objective assessment of image quality of the improvement gained from respiratory-gated PET is mainly limited to a three-dimensional (3D) approach. This work proposes a 4D numerical observer that incorporates both spatial and temporal informations for detection tasks in pulmonary oncology.

METHODS

The authors propose a 4D numerical observer constructed with a 3D channelized Hotelling observer for the spatial domain followed by a Hotelling observer for the temporal domain. Realistic (18)F-fluorodeoxyglucose activity distributions were simulated using a 4D extended cardiac torso anthropomorphic phantom including 12 spherical lesions at different anatomical locations (lower, upper, anterior, and posterior) within the lungs. Simulated data based on Monte Carlo simulation were obtained using geant4 application for tomographic emission (GATE). Fifty noise realizations of six respiratory-gated PET frames were simulated by GATE using a model of the Siemens Biograph mMR scanner geometry. PET sinograms of the thorax background and pulmonary lesions that were simulated separately were merged to generate different conditions of the lesions to the background (e.g., lesion contrast and motion). A conventional ordered subset expectation maximization (OSEM) reconstruction (5 iterations and 6 subsets) was used to obtain: (1) gated, (2) nongated, and (3) motion-corrected image volumes (a total of 3200 subimage volumes: 2400 gated, 400 nongated, and 400 motion-corrected). Lesion-detection signal-to-noise ratios (SNRs) were measured in different lesion-to-background contrast levels (3.5, 8.0, 9.0, and 20.0), lesion diameters (10.0, 13.0, and 16.0 mm), and respiratory motion displacements (17.6-31.3 mm). The proposed 4D numerical observer applied on multiple-gated images was compared to the conventional 3D approach applied on the nongated and motion-corrected images.

RESULTS

On average, the proposed 4D numerical observer improved the detection SNR by 48.6% (p < 0.005), whereas the 3D methods on motion-corrected images improved by 31.0% (p < 0.005) as compared to the nongated method. For all different conditions of the lesions, the relative SNR measurement (Gain = SNRObserved/SNRNongated) of the 4D method was significantly higher than one from the motion-corrected 3D method by 13.8% (p < 0.02), where Gain4D was 1.49 ± 0.21 and Gain3D was 1.31 ± 0.15. For the lesion with the highest amplitude of motion, the 4D numerical observer yielded the highest observer-performance improvement (176%). For the lesion undergoing the smallest motion amplitude, the 4D method provided superior lesion detectability compared with the 3D method, which provided a detection SNR close to the nongated method. The investigation on a structure of the 4D numerical observer showed that a Laguerre-Gaussian channel matrix with a volumetric 3D function yielded higher lesion-detection performance than one with a 2D-stack-channelized function, whereas a different kind of channels that have the ability to mimic the human visual system, i.e., difference-of-Gaussian, showed similar performance in detecting uniform and spherical lesions. The investigation of the detection performance when increasing noise levels yielded decreasing detection SNR by 27.6% and 41.5% for the nongated and gated methods, respectively. The investigation of lesion contrast and diameter showed that the proposed 4D observer preserved the linearity property of an optimal-linear observer while the motion was present. Furthermore, the investigation of the iteration and subset numbers of the OSEM algorithm demonstrated that these parameters had impact on the lesion detectability and the selection of the optimal parameters could provide the maximum lesion-detection performance. The proposed 4D numerical observer outperformed the other observers for the lesion-detection task in various lesion conditions and motions.

CONCLUSIONS

The 4D numerical observer shows substantial improvement in lesion detectability over the 3D observer method. The proposed 4D approach could potentially provide a more reliable objective assessment of the impact of respiratory-gated PET improvement for lesion-detection tasks. On the other hand, the 4D approach may be used as an upper bound to investigate the performance of the motion correction method. In future work, the authors will validate the proposed 4D approach on clinical data for detection tasks in pulmonary oncology.

Direct reconstruction of cardiac PET kinetic parametric images using a preconditioned conjugate gradient approach

PURPOSE

Our research goal is to develop an algorithm to reconstruct cardiac positron emission tomography (PET) kinetic parametric images directly from sinograms and compare its performance with the conventional indirect approach.

METHODS

Time activity curves of a NCAT phantom were computed according to a one-tissue compartmental kinetic model with realistic kinetic parameters. The sinograms at each time frame were simulated using the activity distribution for the time frame. The authors reconstructed the parametric images directly from the sinograms by optimizing a cost function, which included the Poisson log-likelihood and a spatial regularization terms, using the preconditioned conjugate gradient (PCG) algorithm with the proposed preconditioner. The proposed preconditioner is a diagonal matrix whose diagonal entries are the ratio of the parameter and the sensitivity of the radioactivity associated with parameter. The authors compared the reconstructed parametric images using the direct approach with those reconstructed using the conventional indirect approach.

RESULTS

At the same bias, the direct approach yielded significant relative reduction in standard deviation by 12%-29% and 32%-70% for 50 × 10(6) and 10 × 10(6) detected coincidences counts, respectively. Also, the PCG method effectively reached a constant value after only 10 iterations (with numerical convergence achieved after 40-50 iterations), while more than 500 iterations were needed for CG.

CONCLUSIONS

The authors have developed a novel approach based on the PCG algorithm to directly reconstruct cardiac PET parametric images from sinograms, and yield better estimation of kinetic parameters than the conventional indirect approach, i.e., curve fitting of reconstructed images. The PCG method increases the convergence rate of reconstruction significantly as compared to the conventional CG method.