Percent Contrast Research Articles

Quantitative analysis of the effect of the magnetic field generated by a PET/MR scanner on positron range

Image quality in positron emission tomography (PET) is influenced by positron range. In this work, the effect of the magnetic field of a PET/MR Siemens Biograph mMR 3T on the quality of PET images was studied. Experimental measurements were conducted using18F and68Ga-filled phantoms to quantify image uniformity, recovery coefficients (RCs), spill-over ratios and percent contrast for spherical lesions. Tissue-equivalent phantoms (lung inhale and exhale, adipose, water, trabecular and cortical bone) were used together with a line source to quantify the impact of the magnetic field on the reconstructed PET images. A comparative analysis was made with images obtained with a PET/CT Biograph Vision 600, using the same radionuclides and phantoms. Higher RCs values were obtained when the image quality phantom was filled with68Ga and scanned with the PET/MR system compared to those obtained with the PET/CT scanner. Hot spheres in the lesion detectability phantom, appear contracted in the transverse direction in the PET/MR system, an effect more evident for68Ga compared to18F, but no elongation in the direction parallel to the magnetic field was observed. In the PET/CT scanner, radial profiles taken from axial slices of line sources, show longer distribution tails extending beyond 20 mm when filled with68Ga and placed inside lung-inhale tissue. In the PET/MR scanner the radial profiles of all materials collapsed into a single distribution with tails extending no more than 10 mm in the direction perpendicular to the magnetic field. Positron range depends on positron energy and material density in which they traverse. The results show an evident improvement in image quality in the transaxial direction only, particularly in phantoms filled with68Ga when using a PET/MR system as opposed to images acquired in the PET/CT system due to the presence of the magnetic field.

Feasibility of noise-reduction reconstruction technology based on non-local-mean principle in SiPM-PET/CT

Quantitative values of positron emission tomography (PET) images using non-local-mean in a silicon photomultiplier (SiPM)-PET/computed tomography (CT) system with phantom and clinical images.The evaluation was conducted on a National Electrical Manufacturers Association body phantom with micro-spheres (4, 5, 6, 8, 10, 13 mm) and clinical images using the SiPM-PET/CT system.The signal-to-background ratio of the phantom was set to 4, and all PET image data was obtained and reconstructed using three-dimensional ordered subset expectation maximization, time-of-flight, point-spread function, and a 4-mm Gaussian filter (GF) and clear adaptive low-noise method (CaLM) in mild, standard, and strong intensities.The evaluation included the standardized uptake value (SUV), percent contrast (QH), coefficient of variation of the background area (CVbackground) clinical imaging for SUV of lung nodules, liver signal-to-noise ratio (SNR), and visual evaluation.SUVmax for 8-mm sphere in phantom images at 2 min for GF and CaLM (mild, standard, strong) were 2.11, 2.32, 2.02, and 1.72; the QH, 8 mm was 27.33 %, 27.47 %, 21.81 %, and 16.09 %; and CVbackground was 12.78, 11.35, 7.86, and 4.71, respectively.CaLM demonstrated higher SUVmax in clinical images than GF for all lung nodule sizes. The average SUVmax for nodules with a diameter of ≤ 1 cm were 5.9 ± 2.4, 9.9 ± 4.9, 9.9 ± 5.0, and 9.9 ± 5.0 for GF and CaLM-mild, standard, and strong intensities, respectively.Liver SNRs were higher for CaLM (mild, standard, strong) compared to GF, with increasing CaLM intensity causing higher liver SNR. CaLM-mild and standard demonstrated suitability for diagnosis in visual evaluation.

Altered gray-to-white matter tissue contrast in preterm-born adults.

To investigate cortical organization in brain magnetic resonance imaging (MRI) of preterm-born adults using percent contrast of gray-to-white matter signal intensities (GWPC), which is an in vivo proxy measure for cortical microstructure. Using structural MRI, we analyzed GWPC at different percentile fractions across the cortex (0%, 10%, 20%, 30%, 40%, 50%, and 60%) in a large and prospectively collected cohort of 86 very preterm-born (<32 weeks of gestation and/or birth weight <1500 g, VP/VLBW) adults and 103 full-term controls at 26 years of age. Cognitive performance was assessed by full-scale intelligence quotient (IQ) using the Wechsler Adult Intelligence Scale. GWPC was significantly decreased in VP/VLBW adults in frontal, parietal, and temporal associative cortices, predominantly in the right hemisphere. Differences were pronounced at 20%, 30%, and 40%, hence, in middle cortical layers. GWPC was significantly increased in right paracentral lobule in VP/VLBW adults. GWPC in frontal and temporal cortices was positively correlated with birth weight, and negatively with duration of ventilation (p < 0.05). Furthermore, GWPC in right paracentral lobule was negatively correlated with IQ (p < 0.05). Widespread aberrant gray-to-white matter contrast suggests lastingly altered cortical microstructure after preterm birth, mainly in middle cortical layers, with differential effects on associative and primary cortices.

Evaluation of data-driven respiratory gating for subcentimeter lesions using digital PET/CT system and three-axis motion phantom

Introduction. The application of data-driven respiratory gating (DDG) for subcentimeter lesions with respiratory movement remains poorly understood. Hence, this study aimed to clarify DDG application for subcentimeter lesions and the ability of digital Positron emission tomography/computed tomography (PET/CT) system combined with DDG to detect these lesions under three-axis respiration. Methods. Discovery MI PET/CT system and National Electrical Manufacturers Association (NEMA) body phantom with Micro Hollow Sphere (4, 5, 6, 8, 10, and 13 mm) were used. The NEMA phantom was filled with 18F-FDG solutions of 42.4 and 5.3 kBq/ml for each hot sphere and background region. The 3.6 s cycles of three-axis respiratory motion were reproduced using the motion platform UniTraQ. The PET data acquisition was performed in stationary and respiratory-moving states. The data were reconstructed in three PET groups: stationary (NM-PET), no gating with respiratory movement (NG-PET), and DDG gating with respiratory movement (DDG-PET) groups. For image quality, percent contrast (QH); maximum, peak, and mean standardized uptake value (SUV); background region; and detectability index (DI) were evaluated in each PET group. Visual assessment was also conducted. Results. The groups with respiratory movement had deteriorated QH and SUVs compared with NM-PET. Compared with NG-PET, DDG-PET has significantly improved QH and SUVs in spheres above 6 mm. The background region showed no significant difference between groups. The SUVmax, SUVpeak, and QH values of 8 mm sphere were highest in NM-PET, followed by DDG-PET and NG-PET. In visual assessment, the spheres above 6 mm were detected in all PET groups. DDG application did not detect new lesions, but it increased DI and visual score. Conclusions. The application of principal component analysis (PCA)-based DDG algorithm improves both image quality and quantitative SUVs in subcentimeter lesions measuring above 6 mm. Although DDG application cannot detect new subcentimeter lesions, it increases the visual indices.

Evaluation of the performance of a high-resolution time-of-flight PET system dedicated to the head and breast according to NEMA NU 2-2012 standard

BackgroundThis study evaluated the physical performance of a positron emission tomography (PET) system dedicated to the head and breast according to the National Electrical Manufacturers Association (NEMA) NU2-2012 standard.MethodsThe spatial resolution, sensitivity, scatter fraction, count rate characteristics, corrections for count losses and randoms, and image quality of the system were determined. All measurements were performed according to the NEMA NU2-2012 acquisition protocols, but image quality was assessed using a brain-sized phantom. Furthermore, scans of the three-dimensional (3D) Hoffmann brain phantom and mini-Derenzo phantom were acquired to allow visual evaluation of the imaging performance for small structures.ResultsThe tangential, radial, and axial full width at half maximum (FWHM) at a 10-mm offset in half the axial field of view were measured as 2.3, 2.5, and 2.9 mm, respectively. The average system sensitivity at the center of the field of view and at a 10-cm radial offset was 7.18 and 8.65 cps/kBq, respectively. The peak noise-equivalent counting rate was 35.2 kcps at 4.8 kBq/ml. The corresponding scatter fraction at the peak noise-equivalent counting rate was 46.8%. The peak true rate and scatter fraction at 8.6 kBq/ml were 127.8 kcps and 54.3%, respectively. The percent contrast value for a 10-mm sphere was approximately 50%. On the 3D Hoffman brain phantom image, the structures of the thin layers composing the phantom were visualized on the sagittal and coronal images. On the mini-Derenzo phantom, each of the 1.6-mm rods was clearly visualized.ConclusionTaken together, these results indicate that the head- and breast-dedicated PET system has high resolution and is well suited for clinical PET imaging.

Computed tomography in the differential diagnosis of adrenal tumors

Background. Modern methods of topical diagnostics have high accuracy and can determine the morphological structure of the adrenal tumor with high probability before surgery, but none of them has 100% sensitivity and specificity. Contrast-enhanced computed tomography is most commonly used by clinicians. The criteria for the malignancy of an adrenal tumor determined by this method continue to be discussed.The aim is to evaluate the effectiveness of contrast-enhanced computed tomography in the preoperative diagnosis of adrenal tumors and to analyze errors.Materials and methods. Contrast-enhanced computed tomography was performed in 69 patients with adrenal tumors. After morphological examination of the removed tumors, the effectiveness of preoperative diagnostics was evaluated with the determination of sensitivity and specificity of the method. If the pre- and postoperative diagnosis did not match, the causes of errors were analyzed.Results. The attenuation on unenhanced CT in adenomas ranged from 5 to 36 HU, in adrenocortical cancer — from 26 to 80 HU, in pheochromocytomas — from 25 to 99 HU. The attenuation of adenomas on unenhanced CT was significantly less than with pheochromocytomas (p=0.005) and adrenocortical cancer (p=0.012). In the venous phase, no significant differences were found, and in the delayed phase, the attenuation of adenomas was also significantly less than in malignant tumors (p=0.008, p=0.008). The median of absolute percent contrast washout in adenomas was 85%, in pheochromocytes — 59%, in adrenocortical cancer — 57%. When comparing the diagnosis before and after surgery, its non-coincidence was found in 8 cases (10.39%). Two patients (2.59%) with small tumors (diameter of 15 mm) were diagnosed with adenoma in ­combination with pheochromocytoma and adenoma before surgery. After morphological examination, the diagnosis was changed to adrenocortical cancer in combination with adenoma and «mute» pheochromocytoma.Conclusion. The sensitivity and specificity of contrast-enhanced CT in the diagnosis of adenomas was 95.61% and 94.82%, pheochromocytomas — 95% and 95.08%, adrenocortical cancer — 92.31 and 98.48%. Diagnostic errors of «mute» pheochromocytoma and adrenocortical cancer occurred with small sizes (15 mm) of adrenal tumors.

Optimizing 3D Rotational Angiography for Congenital Cardiac Catheterization.

The aim of the study was to determine the variables associated with high-quality (HQ) versus low-quality (LQ) three-dimensional rotational angiography (3DRA) and create guides for optimization of approach to 3DRA in congenital cardiac catheterization (CCC). CCC has adopted 3DRA as a mainstay, but there has not been systematic analysis of approach to and factors associated with HQ 3DRA. This was a single-center, retrospective study of 3DRAs using Canon Infinix-I platform. Reconstructions were graded by 3 interventionalists. Quality was dichotomized into HQ and LQ. Univariable analyses and multivariable logistic regression models were performed. From 8/2016 to 12/2018, 208 3DRAs were performed in 195 CCCs; median age 7 years (2, 16), weight 23kg (12, 57). The majority of 3DRAs were performed in patients with biventricular physiology (N = 137, 66%) and in pulsatile sites (N = 144, 69%). HQ 3DRA (N = 182, 88%) was associated with greater total injection volume [2.20mL/kg (1.44, 3.29) vs. 1.62mL/kg (1.10, 1.98), p = 0.005] and more dilute contrast solution [60% (50, 100) vs. 100% (60, 100), p = 0.007], but not with contrast volume administered (p = 0.2) on univariable analysis. On multivariable logistic regression, HQ 3DRA was significantly associated with patient weight [OR 0.97 (95% CI (0.94, 0.99), p = 0.018], total injection volume [OR 1.04 (95% CI 1.01, 1.07) p = 0.011], and percent contrast solution [OR 0.97 (95% CI 0.95, 1.00), p = 0.022]. These data resulted in creation of scatter plots and a novel 3DRA Nomogram for estimating the probability of HQ 3DRA. This is the first study to create evidence-basedcontrast dose guides and nomogram for 3DRA in CCC. HQ 3DRA was associated with lower weight, higher total injection volumes, and more dilute contrast solution.

Physical performance of adaptive axial FOV PET scanners with a sparse detector block rings or a checkerboard configuration

Objective. Using Monte-Carlo simulations, we evaluated the physical performance of a hypothetical state-of-the-art clinical PET scanner with adaptive axial field-of-view (AFOV) based on the validated GATE model of the Siemens Biograph VisionTM PET/CT scanner. Approach. Vision consists of 16 compact PET rings, each consisting of 152 mini-blocks of 5 × 5 Lutetium Oxyorthosilicate crystals (3.2 × 3.2 × 20 mm3). The Vision 25.6 cm AFOV was extended by adopting (i) a sparse mini-block ring (SBR) configuration of 49.6 cm AFOV, with all mini-block rings interleaved with 16 mm axial gaps, or (ii) a sparse mini-block checkerboard (SCB) configuration of 51.2 cm AFOV, with all mini-blocks interleaved with gaps of 16 mm (transaxial) × 16 mm (axial) width in checkerboard pattern. For sparse configurations, a ‘limited’ continuous bed motion (limited-CBM) acquisition was employed to extend AFOVs by 2.9 cm. Spatial resolution, sensitivity, image quality (IQ), NECR and scatter fraction were assessed per NEMA NU2-2012. Main Results. All IQ phantom spheres were distinguishable with all configurations. SBR and SCB percent contrast recovery (% CR) and background variability (% BV) were similar (p-value > 0.05). Compared to Vision, SBR and SCB %CRs were similar (p-values > 0.05). However, SBR and SCB %BVs were deteriorated by 30% and 26% respectively (p-values < 0.05). SBR, SCB and Vision exhibited system sensitivities of 16.6, 16.8, and 15.8 kcps MBq−1, NECRs of 311 kcps @35 kBq cc−1, 266 kcps @25.8 kBq cc−1, and 260 kcps @27.8 kBq cc−1, and scatter fractions of 31.2%, 32.4%, and 32.6%, respectively. SBR and SCB exhibited a smoother sensitivity reduction and noise enhancement rate from AFOV center to its edges. SBR and SCB attained comparable spatial resolution in all directions (p-value > 0.05), yet, up to 1.5 mm worse than Vision (p-values < 0.05). Significance. The proposed sparse configurations may offer a clinically adoptable solution for cost-effective adaptive AFOV PET with either highly-sensitive or long-AFOV acquisitions.

Application of a Flexible PET Scanner Combined with 3T MRI Using Non-local Means Reconstruction: Qualitative and Quantitative Comparison with Whole-Body PET/CT.

Flexible positron emission tomography (fxPET) employing a non-local means reconstruction algorithm was designed to fit existing magnetic resonance imaging (MRI) systems. We aimed to compare the qualitative and quantitative performance of fxPET among fxPET with MR-based attenuation correction (MRAC), fxPET with CT-based attenuation correction (CTAC) using CT as a part of WB PET/CT, and whole-body (WB) PET/CT. Sixteen patients with suspected head and neck cancer underwent 2-deoxy-2-[18F]fluoro-D-glucose WB PET/CT scans, followed by fxPET and 3T MRI scans. Phantom data were compared among the three datasets. For registration accuracy, we measured the distance between the center of the tumor determined by fxPET and that in MRI. We compared image quality, detection rates, and quantitative values including maximal standardized uptake value (SUVmax), metabolic tumor volume (MTV), total lesion glycolysis (TLG), and tumor-to-muscle ratio (TMR) among the three datasets. The phantom data in fxPET, except the percent contrast recoveries of 17-mm and 22-mm hot spheres, were inferior to those in WB PET/CT. The mean registration accuracy was 4.4mm between fxPET using MRAC and MRI. The image quality was comparable between two fxPET datasets, but significantly inferior to WB PET/CT (p < 0.0001). In contrast, detection rates were comparable among the three datasets. SUVmax was significantly higher, and MTV and TLG were significantly lower in the two fxPET datasets compared with the WB PET/CT dataset (p < 0.005). There were no significant differences in SUVmax, MTV, and TLG between the two fxPET datasets or in TMR among the three datasets. All quantitative values had significantly positive correlations. Compared with WB PET/CT, the phantom data and image quality were inferior in fxPET. However, the results of the detection rates and quantitative values suggested the clinical feasibility of fxPET.

Comparison of Image Quality According to Phantom Fluid Material in MR-based Attenuation Correction PET Imaging in PET/MR

Integrated positron emission tomography (PET)/magnetic resonance (MR) imaging is gradually being used to improve the rate of cancer lesion detection in the medical field. To enhance the quality of PET/MR images, attenuation correction (AC) techniques are used by applying MR pulse sequences of the controlled aliasing in parallel imaging results in higher acceleration (CAIPI; MR ACSUBDixon-Caipi/SUB) and the generation autocalibrating partially parallel acquisition (GRAPPA; MR ACSUBDixon-Grappa/SUB), based on the T1-weighted two-point Dixon pulse sequence. In addition, quality control using a Jaszczak phantom filled with water and radioisotopes is frequently performed when scanning the patient. When acquiring MR-based AC PET images in the phantom study, artifacts are caused by high permittivity in water, and there is a limitation in the acquisition of uniform image quality. Therefore, the purpose of this study was to compare the image quality using phantom fluids with lower permittivity than water (sodium chloride (NaCl) NaCl+nickel sulfate (NiSO₄)) according to MR ACSUBDixon-Caipi/SUB and MR ACSUBDixon-Grappa/SUB pulse sequences using various quantitative analysis parameters: percent of non-uniformity (PNU), percent contrast recovery (PCR), signal to noise ratio (SNR), and coefficient of variation (COV). The results indicated that the image quality with NaCl+NiSO₄ fluid based on the results was 1.2-, 1.6-, 1.4-, and 1.1 times superior to that of NaCl fluid, respectively. In conclusion, NaCl+NiSO₄ fluid is suitable as a phantom fluid material in PET/MR images.

Tumor volume-adapted SUVN as an alternative to SUVpeak for quantification of small lesions in PET/CT imaging: a proof-of-concept study.

SUVpeak is a recommended quantification metric except for small lesions. We aimed to assess the averaged standard uptake value (SUVN) as an alternative to SUVpeak for small-lesion quantification. NEMA-like phantom images were reconstructed using OSEM, OSEM + PSF, OSEM + TOF and OSEM + TOF + PSF with two post-smoothing Gaussian filters for different background activity levels. SUVmax, SUVN (N = 5, 10, 15, 20, 25, 30, 35 or 40 hottest voxels), and SUVpeak, relative percent error, contrast recovery, and volume recovery coefficients were quantified and assessed. SUVN did not have the limitations of SUVpeak for smaller lesions. In the smallest insert at 2.68kBq/ml, optimum N values for OSEM, OSEM + PSF, OSEM + TOF and OSEM + TOF + PSF were 10, 5, 15, and 10 for SUVN, respectively. The same N values were obtained for metabolic tumor volumes (MTVs) for all reconstruction algorithms. At 5.30kBq/ml, N=5 was optimum for SUVN and MTVs. For the larger inserts, the optimum N increased and tended towards the maximum (similar to SUVpeak). SUVN is more accurate than SUVmax or SUVpeak for small lesions, while being as accurate in larger ones. This harmonizing capacity of SUVN can be beneficial for the quantitative analysis of small tumor volumes.

Optimization of scatter estimation window setting for quantitative analysis in 111 In-pentetreotide single photon emission computed tomography imaging.

The aim of this study was to validate the optimal scatter correction method and scatter estimation window setting in terms of image quality and quantitative accuracy for quantitative indium-111 (111In)-pentetreotide SPECT imaging. We used a positron emission tomography/computed tomography (PET/CT) phantom to validate image quality and quantitative accuracy, and the SPECT images were acquired by the multi-energy window (MEW) method. The scatter estimation was performed using four kinds of energy windows (MEW1, MEW2, MEW3, and MEW4). Scatter correction was also performed using a dual-energy window (DEW) for comparison with MEWs. Image quality was assessed using percent contrast (% contrast) and background variability, and quantitative accuracy was assessed using the mean standardized uptake value (SUVmean) with hot spheres. In the quantification, all MEW settings approached the theoretical SUVmean (MEW1, 0.99±0.06; MEW2, 0.99±0.05; MEW3, 1.00±0.08; MEW4, 0.97±0.12) in contrast to DEW (0.88±0.05). The SUVmean value for scatter correction of both photopeaks for a 28 mm sphere showed the smallest difference from the theoretical value. The scatter correction method that gave optimal image quality and quantitative accuracy was MEW3 with two 20% energy windows (one over each photopeak) and four adjacent 3% scatter estimation windows (one on each side of the two photopeaks).

A dedicated phantom design for positron emission mammography performance evaluation

A standard protocol for performance evaluation of positron emission mammography (PEM) systems has not yet been established. In this work we propose a methodology based on the design of specific phantoms for this imaging modality with component dimensions in accordance with typical breast lesion sizes together with the adaptation of current international protocols designed for clinical and preclinical positron emission tomographs (PET) systems. This methodology was used to evaluate the performance of the Flex Solo II PEM scanner in terms of spatial resolution, uniformity and contrast lesion detectability, recovery coefficients and spill-over ratios. Positron range effects were studied with 18F and 68Ga, which have very different energy spectra. Our results indicate that in-plane spatial resolution of the system is around 3.0 mm and 4.4 mm for 18F and 68Ga, respectively. Lesion detectability tests with sphere diameters between 4 and 10 mm confirmed that the PEM system can resolve all the spheres (hot or cold). Percent contrast values for 18F lie between 6%–38% and 34%–51% for hot- and cold- spheres, respectively; the corresponding intervals for 68Ga are lower, 4%–25% and 32%–44%. Regarding uniformity quantification, the system shows percentage standard deviations within 4.9%–5.7%, while the percent background variability measurements ranged between 6.7% and 10.9% for both radionuclides. Recovery coefficients measured with hot rod diameters between 1.5 and 9 mm, have values between 0.2–1.05 and 0.17–0.69 for 18F and 68Ga, respectively. Spill-over ratios have large values (0.22 in average) for both radionuclides. Our results indicate that the phantoms and the methodology developed in this work can serve as the basis for establishing an image quality protocol for the systematic evaluation of PEM systems, with a potential extension for performance evaluation of dedicated breastPET scanners.

Technical Note: Development of an ischemic defect model insert attachable to a commercially available myocardial phantom.

The purpose of this study was to develop a novel myocardial phantom insert model that attaches to commercially available myocardial phantoms and simulates an ischemic area, using three-dimensional printing technology. Ischemic inserts were designed to give four levels of absolute percent contrast (Low; 10%, Medium; 20%, High; 35%, and Defect; 100%) using CT images and computer-aided design software. The ischemic insert was composed of multiple slit structures to replicate myocardial ischemia. Myocardial phantom images with developed ischemic inserts were acquired using a SPECT/CT system and were then reconstructed using filtered back projection (FBP) and iterative reconstruction (IR) with various cutoff frequencies of a Butterworth filter. The performance and utility of ischemic inserts were evaluated according to percent contrast and 5-point scoring. The percent contrast and scoring results changed according to the ischemic insert type, cutoff frequency, and reconstruction method. The percent contrast of each insert obtained by FBP with 0.4 cycles/cm was 4.1% (Low), 15.7% (Medium), 17.4% (High), and 36.1% (Defect). Similarly, the percent contrast of each insert obtained by IR with 0.4 cycles/cm was 5.0% (Low), 17.0% (Medium), 21.9% (High), and 47.7% (Defect). We successfully developed an ischemic insert that attaches to a commercially available myocardial phantom by using CT imaging and 3D printing technology. Our proposed ischemic insert provided several abnormal perfusion patterns on myocardial SPECT images and may be useful for evaluating SPECT image quality.

Utility of the 10 Hounsfield unit threshold for identifying adrenal adenomas: Can we improve?

BackgroundCurrent recommendations using Hounsfield units (HU) ≤ 10 to identify adrenal adenomas on unenhanced computed tomography (CT) miss 10–40% of benign adenomas. We sought to determine if changing HU threshold and adding absolute percent contrast washout (APW) criteria would identify adrenal adenomas better than current recommendations. MethodsImaging characteristics were compared between patients with adenomas (n = 128) and those with non-adenomas (n = 54) after unilateral adrenalectomy. Sensitivity, specificity, positive and negative predictive values (PPV, NPV) were calculated. ResultsUsing HU ≤ 10 to identify adenomas had a sensitivity of 47.6%, specificity of 93.3% (AUC = 0.71, p < 0.001), PPV of 95.3%, and NPV of 58.1% for identifying adrenal adenomas. Applying HU ≤ 16 improved sensitivity (65.4%) without reducing specificity (93.3%) (AUC = 0.79, p < 0.001), PPV increased to 96.3%, and NPV decreased to 47.6%. Applying HU ≤ 16 as the initial criterion followed by APW > 60% for lesions exceeding 16 HU, sensitivity increased to 93.4%, specificity was 93.3% and PPV 96.6%, and NPV improved to 85.7% (AUC = 0.96, p < 0.001). ConclusionsCriteria of initial threshold of HU ≤ 16 followed by APW > 60% for lesions exceeding 16 HU yielded improved sensitivity and specificity in identification of adrenal adenomas.

Physical performance of a long axial field-of-view PET scanner prototype with sparse rings configuration: A Monte Carlo simulation study.

There is a growing interest in extending the axial fields-of-view (AFOV) of PET scanners. One major limitation for the widespread clinical adoption of such systems is the multifold increase in the associated material costs. In this study, we propose a cost-effective solution to extend the PET AFOV using a sparse detector rings configuration. The corresponding physical performance was validated using Monte Carlo simulations. Monte Carlo model of the Siemens BiographTM mCT PET/CT, with a 21.8cm AFOV and a set of compact rings of LSO crystals was developed as a gold standard. The mCT configuration was then modified by interleaving the LSO crystals in the axial direction within each detector block with 4mm physical gaps (equivalent to the LSO crystal axial dimension) thus extending the AFOV to 43.6cm (Ex-mCT). The physical performances of the two MC models were assessed and then compared using NEMA NU 2-2007 standards. Ex-mCT showed <0.2mm difference in transaxial spatial resolution, and, 0.8mm and 0.3mm deterioration in axial spatial resolution, compared to the mCT, at 1 and 10cm off-center of the transaxial field-of-view respectively. The system sensitivities for the mCT and Ex-mCT models were 9.4±0.2 and 10.75±0.2cps/kBq respectively. The higher sensitivity of Ex-mCT was due to four additional detector rings required to double the mCT AFOV. PET images of the NEMA Image Quality (IQ) phantom showed no artifacts due to detector rings sparsity, and all spheres were visible in both configurations. Ex-mCT achieved percent contrast recoveries within 5.6% of those of the mCT for all spheres and a maximum of 36% higher background variability at the center of the AFOV. The Ex-mCT, however, showed a more uniform noise distribution over an axial range of almost twice the length of the mCT AFOV. Using the proposed sparse detector-ring configuration, the AFOV of current generation PET systems can be doubled while maintaining the original number and volume of detector crystal elements, and without jeopardizing the system's overall physical performance. Despite an increase in the noise level, the Ex-mCT exhibited an improved noise uniformity.

Whole body MRI in multiple myeloma: Optimising image acquisition and read times.

To identify the whole-body MRI (WB-MRI) image type(s) with the highest value for assessment of multiple myeloma, in order to optimise acquisition protocols and read times. Thirty patients with clinically-suspected MM underwent WB-MRI at 3 Tesla. Unenhanced Dixon images [fat-only (FO) and water-only (WO)], post contrast Dixon [fat-only plus contrast (FOC) and water-only plus contrast (WOC)] and diffusion weighted images (DWI) of the pelvis from all 30 patients were randomised and read by three experienced readers. For each image type, each reader identified and labelled all visible myeloma lesions. Each identified lesion was compared with a composite reference standard achieved by review of a complete imaging dataset by a further experienced consultant radiologist to determine truly positive lesions. Lesion count, true positives, sensitivity, and positive predictive value were determined. Time to read each scan set was recorded. Confidence for a diagnosis of myeloma was scored using a Likert scale. Conspicuity of focal lesions was assessed in terms of percent contrast and contrast to noise ratio (CNR). Lesion count, true positives, sensitivity and confidence scores were significantly higher when compared to other image types for DWI (P<0.0001 to 0.003), followed by WOC (significant for sensitivity (P<0.0001 to 0.004), true positives (P = 0.003 to 0.049) and positive predictive value (P< 0.0001 to 0.006)). There was no statistically significant difference in these metrics between FO and FOC. Percent contrast was highest for WOC (P = 0.001 to 0.005) and contrast to noise ratio (CNR) was highest for DWI (P = 0.03 to 0.05). Reading times were fastest for DWI across all observers (P< 0.0001 to 0.014). Observers detected more myeloma lesions on DWI images and WOC images when compared to other image types. We suggest that these image types should be read preferentially by radiologists to improve diagnostic accuracy and reporting efficiency.

The visual quality of annual growth increments in fish otoliths increases with latitude

This study evaluated the latitudinal influence on otolith readability through average percent error (APE) assessments and contrast ratios evaluations of the opaque and translucent incremental zones in Micropogonias furnieri otoliths (n = 83) sampled along the Southwestern Atlantic Ocean. Otolith images show well-structured increments in high latitudes. Contrast ratios increased and APE decreased significantly with latitude, respectively, therefore suggesting that M. furnieri otolith visual quality and growth increment readability increase with latitude.

Comparison of PET image quality using simultaneous PET/MR by attenuation correction with various MR pulse sequences

Abstract Positron emission tomography (PET)/magnetic resonance (MR) scanning has the advantage of less additional exposure to radiation than does PET/computed tomography (CT). In particular, MR based attenuation correction (MR AC) can greatly affect the image quality of PET and is frequently obtained using various MR sequences. Thus, the purpose of the current study was to quantitatively compare the image quality between MR non-AC (MR NAC) and MR AC in PET images with three MR sequences. Percent image uniformity (PIU), percent contrast recovery (PCR), and percent background variability (PBV) were estimated to evaluate the quality of PET images with MR AC. Based on the results of PIU, 15.2% increase in the average quality was observed for PET images with MR AC than for PET images with MR NAC. In addition, 28.6% and 71.1% improvement in the average results of PCR and PBV respectively, was observed for PET images with MR AC compared with that with MR NAC. Moreover, no significant difference was observed among the average values using three MR sequences. In conclusion, the current study demonstrated that PET with MR AC improved the image quality and can be help diagnosis in all MR sequence cases.

Deep learning-based stenosis quantification from coronary CT Angiography.

Coronary computed tomography angiography (CTA) allows quantification of stenosis. However, such quantitative analysis is not part of clinical routine. We evaluated the feasibility of utilizing deep learning for quantifying coronary artery disease from CTA. A total of 716 diseased segments in 156 patients (66 ± 10 years) who underwent CTA were analyzed. Minimal luminal area (MLA), percent diameter stenosis (DS), and percent contrast density difference (CDD) were measured using semi-automated software (Autoplaque) by an expert reader. Using the expert annotations, deep learning was performed with convolutional neural networks using 10-fold cross-validation to segment CTA lumen and calcified plaque. MLA, DS and CDD computed using deep-learning-based approach was compared to expert reader measurements. There was excellent correlation between the expert reader and deep learning for all quantitative measures (r=0.984 for MLA; r=0.957 for DS; and r=0.975 for CDD, p<0.001 for all). The expert reader and deep learning method was not significantly different for MLA (median 4.3 mm2 for both, p=0.68) and CDD (11.6 vs 11.1%, p=0.30), and was significantly different for DS (26.0 vs 26.6%, p<0.05); however, the ranges of all the quantitative measures were within inter-observer variability between 2 expert readers. Our deep learning-based method allows quantitative measurement of coronary artery disease segments accurately from CTA and may enhance clinical reporting.