A method of 2D/3D registration of a statistical mouse atlas with a planar X-ray projection and an optical photo

The development of sophisticated and high throughput whole body small animal imaging technologies has created a need for improved image analysis and increased automation. The registration of a digital mouse atlas to individual images is a prerequisite for automated organ segmentation and uptake quantification. This paper presents a fully-automatic method for registering a statistical mouse atlas with individual subjects based on an anterior–posterior X-ray projection and a lateral optical photo of the mouse silhouette. The mouse atlas was trained as a statistical shape model based on 83 organ-segmented micro-CT images. For registration, a hierarchical approach is applied which first registers high contrast organs, and then estimates low contrast organs based on the registered high contrast organs. To register the high contrast organs, a 2D-registration-back-projection strategy is used that deforms the 3D atlas based on the 2D registrations of the atlas projections. For validation, this method was evaluated using 55 subjects of preclinical mouse studies. The results showed that this method can compensate for moderate variations of animal postures and organ anatomy. Two different metrics, the Dice coefficient and the average surface distance, were used to assess the registration accuracy of major organs. The Dice coefficients vary from 0.31 ± 0.16 for the spleen to 0.88 ± 0.03 for the whole body, and the average surface distance varies from 0.54 ± 0.06 mm for the lungs to 0.85 ± 0.10 mm for the skin. The method was compared with a direct 3D deformation optimization (without 2D-registration-back-projection) and a single-subject atlas registration (instead of using the statistical atlas). The comparison revealed that the 2D-registration-back-projection strategy significantly improved the registration accuracy, and the use of the statistical mouse atlas led to more plausible organ shapes than the single-subject atlas. This method was also tested with shoulder xenograft tumor-bearing mice, and the results showed that the registration accuracy of most organs was not significantly affected by the presence of shoulder tumors, except for the lungs and the spleen.     

Cortical surface shift estimation using stereovision and optical flow motion tracking via projection image registration

Stereovision is an important intraoperative imaging technique that captures the exposed parenchymal surface noninvasively during open cranial surgery. Estimating cortical surface shift efficiently and accurately is critical to compensate for brain deformation in the operating room (OR). In this study, we present an automatic and robust registration technique based on optical flow (OF) motion tracking to compensate for cortical surface displacement throughout surgery. Stereo images of the cortical surface were acquired at multiple time points after dural opening to reconstruct three-dimensional (3D) texture intensity-encoded cortical surfaces. A local coordinate system was established with its z-axis parallel to the average surface normal direction of the reconstructed cortical surface immediately after dural opening in order to produce two-dimensional (2D) projection images. A dense displacement field between the two projection images was determined directly from OF motion tracking without the need for feature identification or tracking. The starting and end points of the displacement vectors on the two cortical surfaces were then obtained following spatial mapping inversion to produce the full 3D displacement of the exposed cortical surface. We evaluated the technique with images obtained from digital phantoms and 18 surgical cases – 10 of which involved independent measurements of feature locations acquired with a tracked stylus for accuracy comparisons, and 8 others of which 4 involved stereo image acquisitions at three or more time points during surgery to illustrate utility throughout a procedure. Results from the digital phantom images were very accurate (0.05 pixels). In the 10 surgical cases with independently digitized point locations, the average agreement between feature coordinates derived from the cortical surface reconstructions was 1.7–2.1 mm relative to those determined with the tracked stylus probe. The agreement in feature displacement tracking was also comparable to tracked probe data (difference in displacement magnitude was <1 mm on average). The average magnitude of cortical surface displacement was 7.9 ± 5.7 mm (range 0.3–24.4 mm) in all patient cases with the displacement components along gravity being 5.2 ± 6.0 mm relative to the lateral movement of 2.4 ± 1.6 mm. Thus, our technique appears to be sufficiently accurate and computationally efficiency (typically ∼15 s), for applications in the OR.     

Respiratory motion compensation by model-based catheter tracking during EP procedures

In many cases, radio-frequency catheter ablation of the pulmonary veins attached to the left atrium still involves fluoroscopic image guidance. Two-dimensional X-ray navigation may also take advantage of overlay images derived from static pre-operative 3D volumetric data to add anatomical details otherwise not visible under X-ray. Unfortunately, respiratory motion may impair the utility of static overlay images for catheter navigation. We developed a novel approach for image-based 3D motion estimation and compensation as a solution to this problem. It is based on 3D catheter tracking which, in turn, relies on 2D/3D registration. To this end, a bi-plane C-arm system is used to take X-ray images of a special circumferential mapping catheter from two directions. In the first step of the method, a 3D model of the device is reconstructed. Three-dimensional respiratory motion at the site of ablation is then estimated by tracking the reconstructed catheter model in 3D based on bi-plane fluoroscopy. Phantom data and clinical data were used to assess model-based catheter tracking. Our phantom experiments yielded an average 2D tracking error of 1.4 mm and an average 3D tracking error of 1.1 mm. Our evaluation of clinical data sets comprised 469 bi-plane fluoroscopy frames (938 monoplane fluoroscopy frames). We observed an average 2D tracking error of 1.0 ± 0.4 mm and an average 3D tracking error of 0.8 ± 0.5 mm. These results demonstrate that model-based motion-compensation based on 2D/3D registration is both feasible and accurate.     

MP2RAGE,a self bias-field corrected sequence for improved segmentation and T1-mapping at high field

The large spatial inhomogeneity in transmit B₁ field (B₁⁺) observable in human MR images at high static magnetic fields (B₀) severely impairs image quality. To overcome this effect in brain T₁-weighted images, the MPRAGE sequence was modified to generate two different images at different inversion times, MP2RAGE. By combining the two images in a novel fashion, it was possible to create T₁-weigthed images where the result image was free of proton density contrast, T₂? contrast, reception bias field, and, to first order, transmit field inhomogeneity.MP2RAGE sequence parameters were optimized using Bloch equations to maximize contrast-to-noise ratio per unit of time between brain tissues and minimize the effect of B₁⁺ variations through space. Images of high anatomical quality and excellent brain tissue differentiation suitable for applications such as segmentation and voxel-based morphometry were obtained at 3 and 7 T.From such T₁-weighted images, acquired within 12 min, high-resolution 3D T₁ maps were routinely calculated at 7 T with sub-millimeter voxel resolution (0.65–0.85 mm isotropic). T₁ maps were validated in phantom experiments. In humans, the T₁ values obtained at 7 T were 1.15 ± 0.06 s for white matter (WM) and 1.92 ± 0.16 s for grey matter (GM), in good agreement with literature values obtained at lower spatial resolution. At 3 T, where whole-brain acquisitions with 1 mm isotropic voxels were acquired in 8 min, the T₁ values obtained (0.81 ± 0.03 s for WM and 1.35 ± 0.05 for GM) were once again found to be in very good agreement with values in the literature.     

Association between irisin and homocysteine in euglycemic and diabetic subjects

ObjectivesThe aim of study was to explore whether a relationship exists between homocysteine and irisin in type 2 diabetes (T2D) patients—a population with a high risk of developing cardiovascular disease—and euglycemic controls.Design and methods69 T2D patients and 75 control subjects (adjusted by body mass index (BMI)) were included in the study. Irisin and homocysteine concentrations and anthropometric and biochemical variables were determined.ResultsLevels of homocysteine were significantly higher (11.0 ± 3.0 vs 12.4 ± 4.2 μmol/l) and levels of irisin were lower (279 ± 58 vs 263 ± 38 ng/ml) in T2D patients. When both T2D and controls were considered, irisin was found to correlate only with homocysteine (r = − 0.215; p = 0.011). Moreover, a decreasing trend in irisin levels was observed according to homocysteine tertile (p = 0.034).ConclusionsOur results provide evidence of an association between irisin and homocysteine, which may be due to nicotinamide metabolism. The clinical significance of this relationship is unclear, but our findings may prompt further mechanistic research to investigate the role played by irisin in vascular disorders.     

Evaluation of a Kalman-based block matching method to assess the bi-dimensional motion of the carotid artery wall in B-mode ultrasound sequences

We aim at investigating arterial diseases at early stage, by assessing the longitudinal (i.e. in the same direction as the blood flow) motion of the intima-media complex. This recently evidenced phenomenon has been shown to provide relevant and complementary information about vascular health.Our method assesses the longitudinal and radial motion from clinical in vivo B-mode ultrasound sequences. To estimate the trajectory of a selected point during the cardiac cycle, we introduce a block matching method that involves a temporal update of the reference block using a pixel-wise Kalman filter. The filter uses the initial gray-level of the pixel as control signal to avoid divergence due to cumulating errors. The block and search-window sizes are adapted to the tissue of interest.The method was evaluated on image sequences of the common carotid artery, acquired in 57 healthy volunteers and in 25 patients at high cardiovascular risk. Reference trajectories were generated for each sequence by averaging the tracings performed by three observers. Six different computerized techniques were also compared to our method.With a pixel size of 30 μm, the average absolute motion estimation errors were 84 ± 107 μm and 20 ± 19 μm for the longitudinal and radial directions, respectively. This accuracy was of the same order of magnitude as the inter- and intra-observers variability, and smaller than for the other methods. The estimated longitudinal motion amplitude was significantly reduced in at-risk patients compared with healthy volunteers (408 ± 281 μm vs. 643 ± 274 μm, p < 0.0001).Our method can constitute a reliable and time-saving technique to investigate the arterial stiffness in clinical studies, in the objective to detect early-stage atherosclerosis.     

Comparison of blood component preparation methods from whole blood bags based on buffy coat extraction

We compared the data of our quality control laboratory of the blood components according to the blood component preparation method that we used. We prepared blood components from top and top whole blood (WB) bags and manual pooling of buffy coats (BCs) (method I) or from top and bottom WB bags and automated pooling of BCs with OrbiSac (method II). Pooled platelet concentrates (PC) obtained with method II had higher platelet content when compared with pooled PCs obtained with method I (3.5 ± 0.7 × 10¹¹ vs. 2.6 ± 0.8 × 10¹¹; p < 0.001). The hemoglobin content in the RBCs obtained with method I was higher when compared with method II (55 ± 7 g vs. 52.5 ± 6.6 g; p < 0.001).     

Role of NF-E2-related factor 2 in neuroprotective effect of l-carnitine against high glucose-induced oxidative stress in the retinal ganglion cells

l-Carnitine (LC) has protective effects on high glucose-induced oxidative stress in the retinal ganglion cells (RGCs). The aim of this study was to investigate the role of NF-E2-related factor 2 (Nrf2), Kelch like-ECH-associated protein 1 (Keap1), haemoxygenase-1 (HO-1) and γ-glutamyl cysteine synthetase (γ-GCS) in the protective effect of LC on RGCs. RGCs were first processed with high concentrations of glucose. LC treatment at three concentrations (50 μM, 100 μM and 200 μM) was applied to high glucose stimulated RGCs. The expression of Nrf2, Keap1, haemoxygenase-1 (HO-1) and γ-glutamyl cysteine synthetase (γ-GCS) was quantified by Western blot in the treatment and control (high glucose stimulation) groups. In the three LC groups (50 μM, 100 μM and 200 μM), Nrf-2 (0.71 ± 0.04, 0.89 ± 0.05, 1.24 ± 0.05 vs 0.56 ± 0.03, p < 0.05), HO-1 (0.58 ± 0.04, 0.76 ± 0.06, 0.89 ± 0.07 vs 0.25 ± 0.03, p < 0.01), and γ-GCS protein expression (0.66 ± 0.03, 0.79 ± 0.05, 0.84 ± 0.08 vs 0.84 ± 0.08, p < 0.01) was higher than in the control group. The levels of Keap1 protein were in the LC groups were lower than in the control group (0.50 ± 0.03, 0.45 ± 0.02, 0.53 ± 0.03 vs 0.86 ± 0.05, p < 0.01). In conclusion, in high glucose stimulated RGCs, LC treatment was associated with an increased level of Nrf2, HO-1and γ-GCS. LC treatment was also associated with a reduced expression of Keap1 protein. These results suggest that the protective effect of LC treatment on RGCs may be related to Nrf2-Keap1 pathway.     

Tilting for perfusion: Head-up position during cardiopulmonary resuscitation improves brain flow in a porcine model of cardiac arrest

IntroductionCerebral perfusion is compromised during cardiopulmonary resuscitation (CPR). We hypothesized that beneficial effects of gravity on the venous circulation during CPR performed in the head-up tilt (HUT) position would improve cerebral perfusion compared with supine or head-down tilt (HDT).MethodsTwenty-two pigs were sedated, intubated, anesthetized, paralyzed and placed on a tilt table. After 6 min of untreated ventricular fibrillation (VF) CPR was performed on 14 pigs for 3 min with an automated CPR device called LUCAS (L) plus an impedance threshold device (ITD), followed by 5 min of L-CPR + ITD at 0° supine, 5 min at 30° HUT, and then 5 min at 30° HDT. Microspheres were used to measure organ blood flow in 8 pigs. L-CPR + ITD was performed on 8 additional pigs at 0°, 20°, 30°, 40°, and 50° HUT.ResultsCoronary perfusion pressure was 19 ± 2 mmHg at 0° vs. 30 ± 3 at 30° HUT (p < 0.001) and 10 ± 3 at 30° HDT (p < 0.001). Cerebral perfusion pressure was 19 ± 3 at 0° vs. 35 ± 3 at 30° HUT (p < 0.001) and 4 ± 4 at 30° HDT (p < 0.001). Brain–blood flow was 0.19 ± 0.04 ml min⁻¹ g⁻¹ at 0° vs. 0.27 ± 0.04 at 30° HUT (p = 0.01) and 0.14 ± 0.06 at 30° HDT (p = 0.16). Heart blood flow was not significantly different between interventions. With 0, 10, 20, 30, 40 and 50° HUT, ICP values were 21 ± 2, 16 ± 2, 10 ± 2, 5 ± 2, 0 ± 2, −5 ± 2 respectively, (p < 0.001), CerPP increased linearly (p = 0.001), and CPP remained constant.ConclusionDuring CPR, HDT decreased brain flow whereas HUT significantly lowered ICP and improved cerebral perfusion. Further studies are warranted to explore this new resuscitation concept.     

Chest wall segmentation in automated 3D breast ultrasound scans

In this paper, we present an automatic method to segment the chest wall in automated 3D breast ultrasound images. Determining the location of the chest wall in automated 3D breast ultrasound images is necessary in computer-aided detection systems to remove automatically detected cancer candidates beyond the chest wall and it can be of great help for inter- and intra-modal image registration. We show that the visible part of the chest wall in an automated 3D breast ultrasound image can be accurately modeled by a cylinder. We fit the surface of our cylinder model to a set of automatically detected rib-surface points. The detection of the rib-surface points is done by a classifier using features representing local image intensity patterns and presence of rib shadows. Due to attenuation of the ultrasound signal, a clear shadow is visible behind the ribs. Evaluation of our segmentation method is done by computing the distance of manually annotated rib points to the surface of the automatically detected chest wall. We examined the performance on images obtained with the two most common 3D breast ultrasound devices in the market. In a dataset of 142 images, the average mean distance of the annotated points to the segmented chest wall was 5.59 ± 3.08 mm.     

Endoluminal surface registration for CT colonography using haustral fold matching

Computed Tomographic (CT) colonography is a technique used for the detection of bowel cancer or potentially precancerous polyps. The procedure is performed routinely with the patient both prone and supine to differentiate fixed colonic pathology from mobile faecal residue. Matching corresponding locations is difficult and time consuming for radiologists due to colonic deformations that occur during patient repositioning.We propose a novel method to establish correspondence between the two acquisitions automatically. The problem is first simplified by detecting haustral folds using a graph cut method applied to a curvature-based metric applied to a surface mesh generated from segmentation of the colonic lumen. A virtual camera is used to create a set of images that provide a metric for matching pairs of folds between the prone and supine acquisitions. Image patches are generated at the fold positions using depth map renderings of the endoluminal surface and optimised by performing a virtual camera registration over a restricted set of degrees of freedom. The intensity difference between image pairs, along with additional neighbourhood information to enforce geometric constraints over a 2D parameterisation of the 3D space, are used as unary and pair-wise costs respectively, and included in a Markov Random Field (MRF) model to estimate the maximum a posteriori fold labelling assignment.The method achieved fold matching accuracy of 96.0% and 96.1% in patient cases with and without local colonic collapse. Moreover, it improved upon an existing surface-based registration algorithm by providing an initialisation. The set of landmark correspondences is used to non-rigidly transform a 2D source image derived from a conformal mapping process on the 3D endoluminal surface mesh. This achieves full surface correspondence between prone and supine views and can be further refined with an intensity based registration showing a statistically significant improvement (p < 0.001), and decreasing mean error from 11.9 mm to 6.0 mm measured at 1743 reference points from 17 CTC datasets.     

Model driven quantification of left ventricular function from sparse single-beat 3D echocardiography

This paper presents a novel model based segmentation technique for quantification of left ventricular (LV) function from sparse single-beat 3D echocardiographic data acquired with a fast rotating ultrasound (FRU) transducer. This transducer captures cardiac anatomy in a sparse set of radially sampled, curved cross-sections within a single cardiac cycle. The method employs a 3D Active Shape Model of the left ventricle (LV) in combination with local appearance models as prior knowledge to steer the segmentation. A set of local appearance patches generate the model update points for fitting the model to the LV in the curved FRU cross-sections. Updates are then propagated over the dense 3D model mesh to overcome correspondence problems due to the data sparsity, whereas the 3D Active Shape Model serves to retain the plausibility of the generated shape.Leave-one-out cross-validation was carried out on single-beat FRU data from 28 patients suffering from various cardiac pathologies. Detection succeeded in 24 cases, and failed in 4 cases due to large dropouts in echo signal. For the successful 24 cases, detection yielded Point to Point errors of 3.1 ± 1.1 mm, Point to Surface errors of 1.7 ± 0.9 mm and an EF error of 7.3 ± 4.9%. Comparison of fitting on single-beat versus denser multi-beat data showed a similar performance for both types of data irrespective of frame angles of the intersections. Robustness tests with respect to different model initializations showed acceptable performance for initial positions within a range of 26 mm for displacement and 12° for orientation. Furthermore, a comparison study between the proposed method and global LV function measured from MR studies of the same patients showed an underestimation of volumes estimated from echocardiographic data compared to MR derived volumes, similar to other results reported in literature. All experiments demonstrate that the proposed method combines robustness with respect to initialization with an acceptable accuracy, while using sparse single-beat FRU data.     

A ventilation technique for oxygenation and carbon dioxide elimination in CPR: Continuous insufflation of oxygen at three levels of pressure in a pig model

AimPulmonary ventilation remains an important part of cardiopulmonary resuscitation, affecting gas exchange and haemodynamics. We designed and studied an improved method of ventilation for CPR, constructed specifically to support both gas exchange and haemodynamics. This method uses continuous insufflation of oxygen at three levels of pressure, resulting in tri-level pressure ventilation (TLPV). We hypothesized that TLPV improves gas exchange and haemodynamics compared to manual gold standard ventilation (GSV).MethodsIn 14 pigs, ventricular fibrillation was induced and automated CPR performed for 10 min with either TLPV or GSV. After defibrillation, CPR was repeated with the other ventilation method. Gas exchange and haemodynamics were monitored. Data are presented as mean ± standard error of the mean.ResultsTLPV was superior to GSV for PaO₂ (163 ± 36 mmHg difference; P = 0.001), and peak AWP (−20 ± 2 cmH₂O difference; P = 0.000) and higher for mean AWP (8 ± 0.2 cmH₂O difference; P = 0.000). TLPV was comparable to GSV for CPP (5 ± 3 mmHg difference; P = 0.012), VCO₂ (0.07 ± 0.3 mL/min/kg difference; P = 0.001), SvO₂ (4 ± 3%-point; P = 0.001), mean carotid flow (−0.5 ± 4 mL/min difference; P = 0.016), and pH_a (0.00 ± 0.03 difference; P = 0.002). The PaCO₂ data do not provide a conclusive result (4 ± 4 mmHg difference).ConclusionWe conclude that the ventilation strategy with a tri-level pressure cycle performs comparable to an expert, manual ventilator in an automated-CPR swine model.     

The Role of a Low-Dose Ketamine-Midazolam Regimen in the Management of Severe Painful Crisis in Patients With Sickle Cell Disease

ContextAcute pain is one of the main causes of hospital admission in sickle cell disease, with variable intensity and unpredictable onset and duration.ObjectivesWe studied the role of a low-dose intravenous (IV) ketamine-midazolam combination in the management of severe painful sickle cell crisis.MethodsA retrospective analysis was performed with data from nine adult patients who were admitted to the intensive care unit with severe painful sickle cell crises not responding to high doses of IV morphine and other adjuvant analgesics. A ketamine-midazolam regimen was added to the ongoing opioids as an initial bolus of ketamine 0.25 mg/kg, followed by infusion of 0.2–0.25 mg/kg/h. A midazolam bolus of 1 mg followed by infusion of 0.5–1 mg/h was added to reduce ketamine emergence reactions. Reduction in morphine daily requirements and improvement in pain scores were the determinants of ketamine-midazolam effect. The t-tests were used for statistical analysis.ResultsNine patients were assessed, with mean age of 27 ± 11 years. Morphine requirement was significantly lower after adding the IV ketamine-midazolam regimen. The mean ± SD IV morphine requirement (milligram/day) in the pre-ketamine day (D0) was 145.6 ± 16.5, and it was 112 ± 12.2 on Day 1 (D1) of ketamine treatment (P = 0.007). The Numeric Rating Scale scores on D0 ranged from eight to ten (mean 9.1), but improved to range from five to seven (mean 5.7) on D1. There was a significant improvement in pain scores after adding ketamine-midazolam regimen (P = 0.01).ConclusionLow-dose ketamine-midazolam IV infusion might be effective in reducing pain and opioid requirements in patients with sickle cell disease with severe painful crisis. Further controlled studies are required to prove this effect.     

Decúbito prono en paciente portador de dispositivo de extracción extracorpórea de CO2 Novalung®

ObjectiveTo describe the course of a patient with the extracorporeal CO2 removal device and discover the effect of Novalung on ventilation, considering the patient's prone position and its influence on the device's blood flow. To develop a protocol of managing and specific care of a patient with Novalung.Material and methodsA case report of a patient with Novalung in a tertiary hospital ICU unit is reported. Parameters considered are hemodynamic, respiratory, pharmacological, analytical, neuromonitoring, managing of the Novalung and length of decubitus prone cycles. Anova Test, Student's T test, Wilcoxon-Mann Whitney and Spearman correlation. Significance p <0.05.ResultsA 46-year old women with nosocomial pneumonia and acute respiratory failure with indication of Novalung to decrease hypercapnia and optimize ventilatory management of refractory hypoxemia. ICU Stay 26days, MBP 82 ± 9 mmHg, HR 110 ± 6 lpm during the admission, monitoring PICCO 5 days CI 3.2 ± 0.8 l/min/m2, ELWI 33 ± 4 ml, continuous hemofiltration 13.2days with a median removal 50 cc/h. Norepinephrine dose 0.68 ± 0.79 μ/kg/min for 15days. Respiratory parameters during the admission: PO2 59 ± 13 mmHg, PCO2 68 ± 35 mmHg, SatO2 85 ± 12%, PO2/FIO2 69 ± 35, tidal volume 389 ± 141 cc. Novalung® 13days, heparin dose 181.42 ± 145 mIU/Kg/min, Cephalin time 57.56 ± 16.41 sec, O2 flow 7 ± 3 l/min, median blood flow 1030 cc/h, interquartile range 1447-612 cc/h. Prone cycles 4, duration 53 ± 27 hours. With Novalung® PCO2 decreased regardless of position 66 ± 21:56 ± 9, p = 0.005. Tidal volume 512 ± 67:267 ± 72, p = 0.0001. Blood flow on supine-prone position 1053 ± 82:113 ± 112, p = 0.001. There was no link between blood flow and PCO2 (p = 0.2) and between O2 and PO2 flow (p = 0.05). Specific care: pedal and tibial pulse monitoring, keep circuit safe to prevent and detect signs of bleeding, femoral arterial and venous catheter care, coagulation monitoring.CommentsDuring the use of Novalung protective, ventilation, low tidal volumes, decreased pressure plateau, PEEP and hypercapnia were achieved. Blood flow decreased in prone position, but the PCO2 did not increase. The device did not coagulate.     

Effect of different calcineurin inhibitors on AOPP and TAS after kidney transplantation

ObjectivesLittle is known about the influence of calcineurin inhibitors on advanced oxidation protein products (AOPP) and total antioxidant status (TAS) after renal transplantation.Design and methodsAOPP and TAS were evaluated in transplanted patients on different calcineurin inhibitors. Thirty-five patients were treated with cyclosporine A (group A) and 33 with tacrolimus (group B).ResultsOver 6 months, the mean levels of AOPP in group A decreased from 205.9 ± 125.7 to 140.9 ± 78.9 µmol/L and TAS from 1.89 ± 0.30 to 1.75 ± 0.27 mmol/L. In group B, the mean levels of AOPP decreased from 196.5 ± 123.9 to 129.6 ± 63.8 µmol/L and TAS from 1.80 ± 0.39 to 1.78 ± 0.23 mmol/L.ConclusionNo significant differences in AOPP and TAS were found with respect to treatment. The only exception was the higher mean concentration of AOPP at month 1 in group A (p = 0.026).     

Magnetic resonance imaging-guided attenuation correction in whole-body PET/MRI using a sorted atlas approach

Quantitative whole-body PET/MR imaging is challenged by the lack of accurate and robust strategies for attenuation correction. In this work, a new pseudo-CT generation approach, referred to as sorted atlas pseudo-CT (SAP), is proposed for accurate extraction of bones and estimation of lung attenuation properties. This approach improves the Gaussian process regression (GPR) kernel proposed by Hofmann et al. which relies on the information provided by a co-registered atlas (CT and MRI) using a GPR kernel to predict the distribution of attenuation coefficients. Our approach uses two separate GPR kernels for lung and non-lung tissues. For non-lung tissues, the co-registered atlas dataset was sorted on the basis of local normalized cross-correlation similarity to the target MR image to select the most similar image in the atlas for each voxel. For lung tissue, the lung volume was incorporated in the GPR kernel taking advantage of the correlation between lung volume and corresponding attenuation properties to predict the attenuation coefficients of the lung. In the presence of pathological tissues in the lungs, the lesions are segmented on PET images corrected for attenuation using MRI-derived three-class attenuation map followed by assignment of soft-tissue attenuation coefficient. The proposed algorithm was compared to other techniques reported in the literature including Hofmann's approach and the three-class attenuation correction technique implemented on the Philips Ingenuity TF PET/MR where CT-based attenuation correction served as reference. Fourteen patients with head and neck cancer undergoing PET/CT and PET/MR examinations were used for quantitative analysis. SUV measurements were performed on 12 normal uptake regions as well as high uptake malignant regions. Moreover, a number of similarity measures were used to evaluate the accuracy of extracted bones. The Dice similarity metric revealed that the extracted bone improved from 0.58 ± 0.09 to 0.65 ± 0.07 when using the SAP technique compared to Hofmann's approach. This enabled to reduce the SUV_mean bias in bony structures for the SAP approach to -1.7 ± 4.8% as compared to -7.3 ± 6.0% and -27.4 ± 10.1% when using Hofmann's approach and the three-class attenuation map, respectively. Likewise, the three-class attenuation map produces a relative absolute error of 21.7 ± 11.8% in the lungs. This was reduced on average to 15.8 ± 8.6% and 8.0 ± 3.8% when using Hofmann's and SAP techniques, respectively. The SAP technique resulted in better overall PET quantification accuracy than both Hofmann's and the three-class approaches owing to the more accurate extraction of bones and better prediction of lung attenuation coefficients. Further improvement of the technique and reduction of the computational time are still required.