Maximum Contrast-to-noise Ratio Research Articles

Optimizing dual-energy CT technique for iodine-based contrast-to-noise ratio, a theoretical study.

Dual-energy CT (DECT) systems provide valuable material-specific information by simultaneously acquiring two spectral measurements, resulting in superior image quality and contrast-to-noise ratio (CNR) while reducing radiation exposure and contrast agent usage. The selection of DECT scan parameters, including x-ray tube settings and fluence, is critical for the stability of the reconstruction process and hence the overall imagequality. The goal of this study is to propose a systematic theoretical method for determining the optimal DECT parameters for minimal noise and maximum CNR in virtual monochromatic images (VMIs) for fixed subject size and total radiationdose. The noise propagation in the process of projection based material estimation from DECT measurements is analyzed. The main components of the study are the mean pixel variances for the sinogram and monochromatic image and the CNR, which were shown to depend on the Jacobian matrix of the sinograms-to-DECT measurementsmap. Analytic estimates for the mean sinogram and monochromatic image pixel variances and the CNR as functions of tube potentials, fluence, and VMI energy are derived, and then used in a virtual phantom experiment as an objective function for optimizing the tube settings and VMI energy to minimize the image noise and maximize theCNR. It was shown that DECT measurements corresponding to kV settings that maximize the square of Jacobian determinant values over a domain of interest lead to improved stability of basis material reconstructions. Instances of non-uniqueness in DECT were addressed, focusing on scenarios where the Jacobian determinant becomes zero within the domain of interest despite significant spectral separation. The presence of non-uniqueness can lead to singular solutions during the inversion of sinograms-to-DECT measurements, underscoring the importance of considering uniqueness properties in parameter selection. Additionally, the optimal VMI energy and tube potentials for maximal CNR was determined. When the x-ray beam filter material was fixed at 2 mm of aluminum and the photon fluence for low and high kV scans were considered equal, the tube potential pair of 60/120 kV led to the maximal iodine CNR in the VMI at 53keV. Optimizing DECT scan parameters to maximize the CNR can be done in a systematic way. Also, choosing the parameters that maximize the Jacobian determinant over the set of expected line integrals leads to more stable reconstructions due to the reduced amplification of the measurement noise. Since the values of the Jacobian determinant depend strongly on the imaging task, careful consideration of all of the relevant factors is needed when implementing the proposedframework.

Imaging of intracranial hemorrhage in photon counting computed tomography using virtual monoenergetic images

PurposeTo determine the optimal virtual monoenergetic image (VMI) for detecting and assessing intracranial hemorrhage in unenhanced photon counting CT of the head based on the evaluation of quantitative and qualitative image quality parameters.MethodsSixty-three patients with acute intracranial hemorrhage and unenhanced CT of the head were retrospectively included. In these patients, 35 intraparenchymal, 39 intraventricular, 30 subarachnoidal, and 43 subdural hemorrhages were selected. VMIs were reconstructed using all available monoenergetic reconstruction levels (40–190 keV). Multiple regions of interest measurements were used for evaluation of the overall image quality, and signal, noise, signal-to-noise-ratio (SNR), and contrast-to-noise-ratio (CNR) of intracranial hemorrhage. Based on the results of the quantitative analysis, specific VMIs were rated by five radiologists on a 5-point Likert scale.ResultsSignal, noise, SNR, and CNR differed significantly between different VMIs (p < 0.001). Maximum CNR for intracranial hemorrhage was reached in VMI with keV levels > 120 keV (intraparenchymal 143 keV, intraventricular 164 keV, subarachnoidal 124 keV, and subdural hemorrhage 133 keV). In reading, no relevant superiority in the detection of hemorrhage could be demonstrated using VMIs above 66 keV.ConclusionFor the detection of hemorrhage in unenhanced CT of the head, the quantitative analysis of the present study on photon counting CT is generally consistent with the findings from dual-energy CT, suggesting keV levels just above 120 keV and higher depending on the location of the hemorrhage.However, on the basis of the qualitative analyses, no reliable statement can yet be made as to whether an additional VMI with higher keV is truly beneficial in everyday clinical practice.

Investigation of PET image quality with acquisition time/bed and enhancement of lesion quantification accuracy through deep progressive learning

ObjectiveTo improve the PET image quality by a deep progressive learning (DPL) reconstruction algorithm and evaluate the DPL performance in lesion quantification.MethodsWe reconstructed PET images from 48 oncological patients using ordered subset expectation maximization (OSEM) and deep progressive learning (DPL) methods. The patients were enrolled into three overlapped studies: 11 patients for image quality assessment (study 1), 34 patients for sub-centimeter lesion quantification (study 2), and 28 patients for imaging of overweight or obese individuals (study 3). In study 1, we evaluated the image quality visually based on four criteria: overall score, image sharpness, image noise, and diagnostic confidence. We also measured the image quality quantitatively using the signal-to-background ratio (SBR), signal-to-noise ratio (SNR), contrast-to-background ratio (CBR), and contrast-to-noise ratio (CNR). To evaluate the performance of the DPL algorithm in quantifying lesions, we compared the maximum standardized uptake values (SUVmax), SBR, CBR, SNR and CNR of 63 sub-centimeter lesions in study 2 and 44 lesions in study 3.ResultsDPL produced better PET image quality than OSEM did based on the visual evaluation methods when the acquisition time was 0.5, 1.0 and 1.5 min/bed. However, no discernible differences were found between the two methods when the acquisition time was 2.0, 2.5 and 3.0 min/bed. Quantitative results showed that DPL had significantly higher values of SBR, CBR, SNR, and CNR than OSEM did for each acquisition time. For sub-centimeter lesion quantification, the SUVmax, SBR, CBR, SNR, and CNR of DPL were significantly enhanced, compared with OSEM. Similarly, for lesion quantification in overweight and obese patients, DPL significantly increased these parameters compared with OSEM.ConclusionThe DPL algorithm dramatically enhanced the quality of PET images and enabled more accurate quantification of sub-centimeters lesions in patients and lesions in overweight or obese patients. This is particularly beneficial for overweight or obese patients who usually have lower image quality due to the increased attenuation.

Determining the Optimal Energy Level of Virtual Monoenergetic Images in Dual-Source CT for Diagnosis of Bowel Obstruction and Colitis

Images from 64 patients undergoing an enhanced abdominal-pelvis scan at portal phase in dual-energy CT mode for the diagnosis of colitis or bowel obstruction were retrospectively analyzed. Acquisitions were performed on a third-generation dual-source CT (DSCT) 100/Sn150 kVp. Mixed images were generated, as well as virtual monoenergetic images (VMIs) at 40/50/60/70 keV. Objective image quality was assessed on VMIs and mixed images by measuring contrast, noise and contrast-to-noise ratio (CNR). Noise, smoothing and overall image quality were subjectively analyzed by two radiologists using Likert scales. For both patient groups, the noise decreased significantly according to the energy level from 40 to 60 keV by −47.2 ± 24.0% for bowel obstruction and −50.4 ± 18.2% for colitis. It was similar between 60 and 70 keV (p = 0.475 and 0.059, respectively). Noise values were significantly higher in VMIs than in mixed images, except for 70 keV (p = 0.53 and 0.071, respectively). Similar results were observed for contrast values, with a decrease between 40 and 70 keV of −56.3 ± 7.9% for bowel obstruction −56.2 ± 10.9% for colitis. The maximum CNR value was found at 60 keV compared to other energy levels and mixed images, but there was no significant difference with the other energy levels apart from 70 keV (−9.7 ± 9.8%) for bowel obstruction and 40 keV (−6.6 ± 8.2%) and 70 keV (−5.8 ± 9.2%) for colitis. The VMIs at 60 keV presented higher scores for all criteria for bowel obstruction and colitis, with no significant difference in smoothing score compared to mixed images (p = 0.119 and p = 0.888, respectively).

Photon-Counting Detector CT for Femoral Stent Imaging in an Extracorporeally Perfused Human Cadaveric Model.

This study aims to compare the performance of first-generation dual-source photon-counting detector computed tomography (PCD-CT) to third-generation dual-source energy-integrating detector (EID-CT) regarding stent imaging in the femoral arterial runoff. Continuous extracorporeal perfusion was established in 1 human cadaver using an inguinal and infragenicular access and peristaltic pump. Seven peripheral stents were implanted into both superior femoral arteries by means of percutaneous angioplasty. Radiation dose-equivalent CT angiographies (high-/medium-/low-dose: 10/5/3 mGy) with constant tube voltage of 120 kVp, matching iterative reconstruction algorithm levels, and convolution kernels were used both with PCD-CT and EID-CT. In-stent lumen visibility, luminal and in-stent attenuation as well as contrast-to-noise ratio (CNR) were assessed via region of interest and diameter measurements. Results were compared using analyses of variance and regression analyses. Maximum in-stent lumen visibility achieved with PCD-CT was 94.48% ± 2.62%. The PCD-CT protocol with the lowest lumen visibility (BV40: 78.93% ± 4.67%) performed equal to the EID-CT protocol with the best lumen visibility (BV59: 79.49% ± 2.64%, P > 0.999). Photon-counting detector CT yielded superior CNR compared with EID-CT regardless of kernel and dose level ( P < 0.001). Maximum CNR was 48.8 ± 17.4 in PCD-CT versus 31.28 ± 5.7 in EID-CT (both BV40, high-dose). The theoretical dose reduction potential of PCD-CT over EID-CT was established at 88% (BV40), 83% (BV48/49), and 73% (BV59/60), respectively. In-stent attenuation was not significantly different from luminal attenuation outside stents in any protocol. With superior lumen visibility and CNR, PCD-CT allowed for noticeable dose reduction over EID-CT while maintaining image quality in a continuously perfused human cadaveric model.

Monte Carlo simulation study to explore optimum conditions for Astatine-211 SPECT.

211At is a promising nuclide for targeted radioisotope therapy. Direct imaging of this nuclide is important for in vivo evaluation of its distribution. We investigated suitable conditions for single-photon emission computed tomography (SPECT) imaging of 211At and assessed their feasibility using a homemade Monte Carlo simulation code, MCEP-SPECT. Radioactivity concentrations of 5, 10, or 20kBq/mL were distributed in six spheres in a National Electrical Manufactures Association (NEMA) body phantom with a background of 1kBq/mL. The energy window, projection number, and acquisition time were 71-88keV, 60, and 60s, respectively, per projection. A medium-energy collimator and three low-energy collimators were tested. SPECT images were reconstructed using the ordered subset expectation maximization (OSEM) method with attenuation correction (Chang method) and scatter correction (triple-energy-windows method). Image quality was evaluated using the contrast-to-noise ratio (CNR) for detectability and the contrast recovery coefficient (CRC) for quantitavity. The low-energy, high-sensitivity collimator exhibited the best detectability among the four types of collimators, with a maximum CNR value of 43. In contrast, the low-energy, high-resolution collimator exhibited excellent quantitavity, with a maximum CRC value of 102%. Scatter correction improved the image quality. In particular, the CRC value almost doubled after scatter correction. The detection of spheres smaller than 20mm in diameter was difficult. In summary, low-energy collimators were suitable for the SPECT imaging of 211At. In addition, scatter correction was extremely effective in improving the image quality. The feasibility of 211At SPECT was demonstrated for lesions larger than 20mm.

Imaging properties of Fe3O4@Au and Fe3O4@Bi hybrid nanocomposites as contrast agents in spectral X-ray computed tomography: A Monte Carlo simulation study

Objective(s) In this paper, we evaluated some imaging properties of Fe3O4@Au and Fe3O4@Bi hybrid nanocomposites as contrast agents in spectral CT. For this purpose, we simulated a spectral CT scanner with photon-counting detectors (PCDs) in 6 energy bins by a Monte Carlo simulator.Materials and Methods A cylindrical phantom was designed with a diameter of 8 cm and a height of 10 cm. Fe3O4@Au and Fe3O4@Bi hybrid nanocomposites were designed as a core-shell with a diameter of 80 nm. Simulation results were utilized to reconstruct cross-sectional images through the filtered back-projection (FBP) algorithm in MATLAB software. Signal intensity and contrast to noise ratio (CNR) of tested contrast agents were calculated in spectral CT images. Results The results indicated a comparable image quality for Fe3O4@Au and Fe3O4@Bi hybrid nanocomposites at different energy bins. However, in the energy range of 80 to 120 keV (bin 4 and 5), the difference in signal intensity and CNR between these two nanocomposites increased. The maximum signal intensity and CNR for Fe3O4@Au and Fe3O4@Bi were acquired at the highest concentration. The maximum signal intensity for Fe3O4@Au was 144±10 (HU) in the 4th energy bin and for Fe3O4@Bi 162±19 (HU) in the 5th energy bin. Besides, the maximum CNRs of 74±6 and 67.5±9 for Fe3O4@Au in bin 4, while for Fe3O4@Bi in bin 5 were obtained respectively. Conclusion Based on our results, Fe3O4@Au and Fe3O4@Bi hybrid nanocomposites have provided promising results as contrast agents in spectral CT. Fe3O4@Bi nanocomposites are recommended due to their lower price and availability.

Ferumoxytol-enhanced ultrashort TE MRA and quantitative morphometry of the human kidney vasculature

To evaluate the feasibility of Quantitative Ultrashort-Time-to-Echo Contrast-Enhanced (QUTE-CE) MRA using ferumoxytol as a contrast agent for abdominal angiography in the kidney. Four subjects underwent ferumoxytol-enhanced MRA with the 3D UTE Spiral VIBE WIP sequence at 3T. Image quality metrics were quantified, specifically the blood Signal-to-Noise Ratio (SNR), blood-tissue Contrast-to-Noise Ratio (CNR) and Intraluminal Signal Heterogeneity (ISH) from both the aorta and inferior vena cava (IVC). Morphometric analysis of the vessels was performed using manual approach and semi-automatic approach using Vascular Modeling ToolKit (VMTK). Image quality and branching order were compared between QUTE-CE MRA and the Gadolinium (Gd) CEMRA reference image. QUTE-CE MRA provides a bright blood snapshot that delineates arteries and veins equally in the same scan. The maximum SNR and CNR values were 3,282 ± 1,218 and 1,295 ± 580, respectively - significantly higher than available literature values using other CEMRA techniques. QUTE-CE MRA had lower ISH and depicted higher vessel branching order (7th vs 3rd) within the kidney compared to a standard dynamic clinical Gd CEMRA scan. Morphometric analysis yielded quantitative results for the total kidney volume, total cyst volume and for diameters of the branching arterial network down to the 7th branch. Vessel curvature was significantly increased (p < 0.001) in the presence of a renal cyst compared to equivalent vessels in normal kidney regions. QUTE-CE MRA is feasible for kidney angiography, providing greater detail of kidney vasculature, enabling quantitative morphometric analysis of the abdominal and intra-renal vessels and yielding metrics relevant to vascular diseases while using a contrast agent ferumoxytol that is safe for CKD patients.

Combined gadoxetic acid and gadobenate dimeglumine enhanced liver MRI: a parameter optimization study.

To demonstrate the feasibility of combined delayed-phase gadoxetic acid (GA) and gadobenate dimeglumine (GD) enhanced liver MRI for improved detection of liver metastases, and to optimize contrast agent dose, timing, and flip angle (FA). Fourteen healthy volunteers underwent liver MRI at 3.0T at two visits during which they received two consecutive injections: 1. GA (Visit1 = 0.025mmol/kg; Visit 2 = 0.05mmol/kg) and 2. GD (both visits = 0.1mmol/kg) 20min after GA administration. Two sub-studies were performed: Experiment-1 Eight subjects underwent multi-phase breath-held 3D-fat-saturated T1-weighted spoiled gradient echo (SGRE) imaging to determine the optimal imaging window for the combined GA + GD protocol to create a homogeneously hyperintense liver and vasculature ("plain-white-liver") with maximum contrast to muscle which served as a surrogate for metastatic lesions in both experiments. Experiment-2 Six subjects underwent breath-held 3D-fat-saturated T1-weighted SGRE imaging at three different FA to determine the optimal FA for best image contrast. Signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were evaluated. Experiment-1 The combined GA + GD protocol created a homogeneously hyperintense liver and vasculature with maximum CNR liver/muscle at approximately 60-120s after automatic GD-bolus detection. Experiment-2 Flip angles between 25° and 35° at a dose of 0.025mmol/kg GA provided the best combination that minimized liver/vasculature CNR, while maximizing liver/muscle CNR. CNR performance to achieve a "plain-white-liver" was superior with 0.025mmol/kg GA compared to 0.05mmol/kg. Combined GA + GD enhanced T1-weighted MRI is feasible to achieve a homogeneously "plain-white-liver". Future studies need to confirm that this protocol can improve sensitivity of liver lesion detection in patients with metastatic liver disease.

P045] Neonatal brain: Contrast to noise ratio (CNR) optimization of T1-weighted (T1W) and T2-weighted (T2W) sequences at multiple 1.5T MRI systems, utilizing a neonatal brain tissue mimicking phantom

Purpose To optimize clinical T1w and T2w sequences at multiple 1.5T MRI systems of different vendors, using an in house developed phantom simulating neonatal brain relaxometric characteristics. Materials Methods A neonatal brain phantom, fabricated from paramagnetically doped agarose gel solutions, underwent quantitative MR relaxometry utilizing an Inversion Recovery Spin Echo (IRTSE) method to estimate T1 relaxation times and a Car-Purcell-Meiboom-Gill (CPMG) method to estimate T2 relaxation times at multiple 1.5T MRI systems. Multi-TI turbo spin-echo and multi-TE spin-echo sequences were utilized for direct T1 and T2 relaxation time measurements. Results Signal data S(TR, TE) were reproduced mathematically according to the standard SE signal acquisition equation: S(TR, TE) = PD*(1-exp(-TR/T1)*(exp(-TE/T2). Consequently, TR and TE values at which the maximum CNR between neonatal gray and white matter was recorded were used for the final optimization of T1w and T2w clinical sequences respectively. Based on the above values, TR and TE parameters were modified resulting in an optimized T1wSE sequence TR/TE = 1200 ms/10 ms and an optimized T2wTSE sequence TR/TE = 9500 ms/280 ms as estimated on a clinical MAGNETOM Sonata 1.5T system. Clinical MRI inter-equipment variability for T1 and T2 measurements remained TR and TE parameter variation in optimized T1w and T2w sequences remained less than 7% amongst the selected MRI systems included in this study. Conclusions CNR optimization of T1w and T2w sequences for neonatal brain imaging at multiple 1.5T clinical MRI systems was accomplished with the aid of an in house developed tissue-mimicking phantom.

Cardiac balanced steady-state free precession MRI at 0.35 T: a comparison study with 1.5 T.

While low-field MRI is disadvantaged by a reduced signal-to-noise ratio (SNR) compared to higher fields, it has a number of useful features such as decreased SAR and shorter T1, and has shown promise for diagnostic imaging. This study demonstrates the feasibility of cardiac balanced steady-state free precession (bSSFP) MRI at 0.35 T and compares cardiac bSSFP MRI images at 0.35 T with those at 1.5 T. Cardiac images were acquired in 7 healthy volunteers using an ECG-gated bSSFP cine sequence on a 0.35 T superconducting MR system as well as a clinical 1.5 T system. Blood and myocardium SNR and contrast-to-noise ratio (CNR) were computed. Subjective image scoring was used to compare the image quality between 0.35 and 1.5 T. Cardiac images at 0.35 T were successfully acquired in all volunteers. While the 0.35 T images were noisier than those at 1.5 T, blood, myocardium and papillary muscles could be clearly delineated. At 0.35 T, bSSFP images were acquired at flip angles as high as 150°. Maximum CNR was achieved at 130°. Image quality scoring showed that while at lower flip angles, the 0.35 T images had poorer quality than the 1.5 T, but with flip angles of 110 and 130, the image quality at 0.35 T had scores similar to those at 1.5 T. This study demonstrates that cardiac bSSFP imaging is highly feasible at 0.35 T.

OA017] Fabrication of an anthropomorphic neonatal 3D printed head phantom, to be utilized as a quality assurance means for the optimization of the neonatal brain T1 and T2 weighted sequences on a 1.5T clinical MRI system

Purpose To develop an anthropomorphic neonatal 3D printed head phantom which could be used as a quality assurance means for the overall optimization of the neonatal brain clinical T1-weighted (T1w) and T2-weighted (T2w) MRI pulse sequences. Materials and Methods Tissue-mimicking materials simulating the MR relaxation times of gray and white matter of the neonatal brain were fabricated and enclosed in five glass tube vials. A 3D printed neonatal head anthropomorphic phantom, with radiologically bone-equivalent material was fabricated using anonymized CT scans of a specific neonatal subject. The aforementioned tube vials were encapsidated inside the neonatal head phantom cavity. The anthropomorphic phantom with the encapsidated neonatal brain tissue mimicking glass vials underwent quantitative MR relaxometry utilizing an Inversion Recovery Turbo Spin Echo (IRTSE) sequence to estimate T1 relaxation times and a Car-Purcell-Meiboom-Gill (CPMG) sequence to estimate T2 relaxation times on a clinical 1.5T MRI system. Based on the relaxometric T1 and T2 measurements, the optimal TR and TE values at which the maximum Contrast to Noise Ratio (CNR) between neonatal gray and white matter was recorded were used for the final optimization of the clinical T1w and T2w clinical sequences respectively. Results T1 and T2 relaxation times of the tissue mimicking materials were in concordance with the relaxation times of a real neonatal brain subject. Clinical MRI system’s reproducibility for T1 and T2 measurements remained The anthropomorphic neonatal 3D printed head phantom served as an excellent means for the general optimization of the geometrical, MR signaling and RF safety characteristics, as well as the optimal acquisition times of the clinical neonatal T1w and T2w MRI pulse sequences. Optimal values for the TR and TE MRI parameters were assessed in reference to the maximum CNR between neonatal brain gray and white matter. These were: (TR/TE = 1200 ms/10 ms) for the T1wSE and (TR/TE = 9500 ms/280 ms) for the (T2wTSE) sequences respectively. Conclusion Overall clinical T1w and T2w sequence optimization for neonatal brain imaging at a 1.5T clinical MRI system was accomplished with the aid of an anthropomorphic neonatal 3D printed head phantom encapsidated with neonatal brain tissue mimicking materials.

Using Correlative Properties of Neighboring Pixels to Enhance Contrast-to-Noise Ratio of Abnormal Hippocampus in Patients With Intractable Epilepsy and Mesial Temporal Sclerosis

To test whether an image-processing algorithm can aid in visualization of mesial temporal sclerosis on magnetic resonance imaging by selectively increasing contrast-to-noise ratio (CNR) between abnormal hippocampus and normal brain. In this Institutional Review Board-approved and Health Insurance Portability and Accountability Act-compliant study, baseline coronal fluid-attenuated inversion recovery images of 18 adults (10 females, eight males; mean age 41.2 years) with proven mesial temporal sclerosis were processed using a custom algorithm to produce corresponding enhanced images. Average (Hmean) and maximum (Hmax) CNR for abnormal hippocampus were calculated relative to normal ipsilateral white matter. CNR values for normal gray matter (GM) were similarly calculated using ipsilateral cingulate gyrus as the internal control. To evaluate effect of image processing on visual conspicuity of hippocampal signal alteration, a neuroradiologist masked to the side of hippocampal abnormality rated signal intensity (SI) of hippocampi on baseline and enhanced images using a five-point scale (definitely abnormal to definitely normal). Differences in Hmean, Hmax, GM, and SI ratings for abnormal hippocampi on baseline and enhanced images were assessed for statistical significance. Both Hmean and Hmax were significantly higher in enhanced images as compared to baseline images (p < 0.0001 for both). There was no significant difference in the GM between baseline and enhanced images (p = 0.9375). SI ratings showed a more confident identification of abnormality on enhanced images (p = 0.0001). Image-processing resulted in increased CNR of abnormal hippocampus without affecting the CNR of normal gray matter. This selective increase in conspicuity of abnormal hippocampus was associated with more confident identification of hippocampal signal alteration.

Effect of slice excitation profile on ungated steady state cardiac perfusion imaging

In cardiac perfusion imaging, choice of flip angle is an important factor for steady state acquisition. This work focuses on presenting an analytical framework for understanding how non-ideal slice excitation profiles affect contrast in ungated 2D steady state cardiac perfusion studies, and to study a technique for estimating flip angle that maximizes enhanced/unenhanced myocardial contrast-to-noise ratio (CNR) in single slice and multi-slice acquisitions. A numerical simulation of ungated 2D golden ratio radial spoiled gradient echo (SPGR) was created that takes into consideration the actual (Bloch simulated) slice excitation profile. The effect of slice excitation profile on myocardial CNR as a function of flip angle was assessed in phantoms and in vivo. For fast RF pulses, the flip angle that yields maximum CNR (considering the actual slice excitation profile) was considerably higher than expected, assuming an ideal excitation. The simulation framework presented accurately predicts the flip angle yielding maximum CNR when the actual slice excitation profile is taken into consideration. The prescribed flip angle for optimal contrast in ungated 2D steady-state SPGR cardiac perfusion studies can vary significantly from that calculated when an ideal slice excitation profile is assumed. Consideration of the actual slice excitation can yield a more optimal flip angle estimate in both the single slice and multi-slice cases.

A study on the imaging characteristics of Gold nanoparticles as a contrast agent in X-ray computed tomography

Abstract Aim: In the current study, some imaging characteristics of AuNPs were quantitatively analyzed and compared with two conventional contrast media (CM) including Iodine and Gadolinium by using of a cylindrical phantom. Methods: AuNPs were synthesized with the mean diameter of 16 nm and were equalized to the concentration of 0.5, 1, 2 and 4 mg/mL in the same volumes. A cylindrical phantom resembling the head and neck was fabricated and drilled to contain small tubes filled with Iodine, Gadolinium, and AuNPs as contrast media. The phantom was scanned in different exposure techniques and CT numbers of three studied contrast media inside test tubes were measured in terms of Hounsfield Unit (HU). The imaging parameters of the noise and contrast to noise ratios (CNR) were calculated for all studied CMs. Results: AuNPs showed 128% and 166% higher CT number in comparison with Iodine and Gadolinium respectively. Also, Iodine had a greater CT number than Gadolinium for the same exposure techniques and concentration. The maximum CT number for AuNPs and studied contrast materials was obtained at the highest mAs and the lowest tube potential. The maximum CT number were 1033±11 (HU) for AuNP, 565±10 (HU) for Iodine, 458±11 for Gadolinium. Moreover, the maximum CNRs of 433±117, 203±53, 145±37 were found for AuNPs, Iodine and Gadolinium respectively. Conclusion: The contrast agent based on AuNPs showed higher imaging quality in terms of contrast and noise relative to other iodine and gadolinium based contrast media in X-ray computed tomography. Application of the AuNPs as a contrast medium in x-ray CT is recommended.

Multiple arterial phase MRI of arterial hypervascular hepatic lesions: improved arterial phase capture and lesion enhancement.

To establish if triple-phase arterial imaging improves the detection of arterial phase hyperintense lesions based on arterial phase capture, motion artifact degradation, and lesion enhancement when compared to single-phase imaging. Patients at risk for hepatocellular carcinoma were imaged at 3.0T. Seventy-three consecutive patients with a standard single-phase MRI and eighty-five consecutive patients were imaged using extracellular contrast with triple arterial phase MRI using three sequential accelerated acquisitions of 8s. Arterial phase capture and image quality were qualitatively categorized. Forty single-phase and forty-four triple-phase studies contained arterially enhancing lesions>1cm with washout appearance. The contrast-to-noise ratio (CNR) of the lesions was calculated. We compared the differences in means with Student t-tests and those in arterial phase capture with a Chi squared test with Yates correction. The triple-phase acquisitions captured the early or late arterial phases more frequently than did the single-phase acquisition (99% vs 86%; P value=0.006). Triple-phase also provided greater number of patients with early or late arterial phase imaging without motion artifact (92% vs 79%, P-value=0.05). The lesion analysis revealed increased maximum CNR in the triple-phase imaging (704.4) vs. single-phase imaging (517.2), P-value<0.001. Triple-phase acquisition provides more robust arterial phase imaging for hepatic lesions, with increased lesion CNR, compared to standard single-phase arterial phase imaging.

Contrast Enhanced Superharmonic Imaging for Acoustic Angiography Using Reduced Form-Factor Lateral Mode Transmitters for Intravascular and Intracavity Applications

Techniques to image the microvasculature may play an important role in imaging tumor-related angiogenesis and vasa vasorum associated with vulnerable atherosclerotic plaques. However, the microvasculature associated with these pathologies is difficult to detect using traditional B-mode ultrasound or even harmonic imaging due to small vessel size and poor differentiation from surrounding tissue. Acoustic angiography, a microvascular imaging technique that utilizes superharmonic imaging (detection of higher order harmonics of microbubble response), can yield a much higher contrast-to-tissue ratio than second harmonic imaging methods. In this paper, two dual-frequency transducers using lateral mode transmitters were developed for superharmonic detection and acoustic angiography imaging in intracavity applications. A single element dual-frequency intravascular ultrasound transducer was developed for concept validation, which achieved larger signal amplitude, better contrast-to-noise ratio (CNR), and pulselength compared to the previous work. A dual-frequency [Pb(Mg1/3Nb2/3)O3]-x[PbTiO3] array transducer was then developed for superharmonic imaging with dynamic focusing. The axial and lateral sizes of the microbubbles in a 200- [Formula: see text] tube were measured to be 269 and [Formula: see text], respectively. The maximum CNR was calculated to be 22 dB. These results show that superharmonic imaging with a low frequency lateral mode transmitter is a feasible alternative to thickness mode transmitters when the final transducer size requirements dictate design choices.

Effect of a Noise-Optimized Second-Generation Monoenergetic Algorithm on Image Noise and Conspicuity of Hypervascular Liver Tumors: An In Vitro and In Vivo Study.

The purpose of this study is to investigate whether the reduction in noise using a second-generation monoenergetic algorithm can improve the conspicuity of hypervascular liver tumors on dual-energy CT (DECT) images of the liver. An anthropomorphic liver phantom in three body sizes and iodine-containing inserts simulating hypervascular lesions was imaged with DECT and single-energy CT at various energy levels (80-140 kV). In addition, a retrospective clinical study was performed in 31 patients with 66 hypervascular liver tumors who underwent DECT during the late hepatic arterial phase. Datasets at energy levels ranging from 40 to 80 keV were reconstructed using first- and second-generation monoenergetic algorithms. Noise, tumor-to-liver contrast-to-noise ratio (CNR), and CNR with a noise constraint (CNRNC) set with a maximum noise increase of 50% were calculated and compared among the different reconstructed datasets. The maximum CNR for the second-generation monoenergetic algorithm, which was attained at 40 keV in both phantom and clinical datasets, was statistically significantly higher than the maximum CNR for the first-generation monoenergetic algorithm (p < 0.001) or single-energy CT acquisitions across a wide range of kilovoltage values. With the second-generation monoenergetic algorithm, the optimal CNRNC occurred at 55 keV, corresponding to lower energy levels compared with first-generation algorithm (predominantly at 70 keV). Patient body size did not substantially affect the selection of the optimal energy level to attain maximal CNR and CNRNC using the second-generation monoenergetic algorithm. A noise-optimized second-generation monoenergetic algorithm significantly improves the conspicuity of hypervascular liver tumors.

Contrast Optimization for an Animal Model of Prostate Cancer MRI at 3T

Purpose: To optimize contrast to noise ratio (CNR) in magnetic resonance imaging (MRI) of prostate cancer using at 3T. Methods: CNR was expressed as a difference in MR signals of two samples. Amulti-echo spin-echo (MESE) pulse sequence was used. The theoretical value of the maximum CNR was obtained using the derivative of CNR with echo time (TE) as a variable. The T1 relaxation time was ignored as repetition time (TR) was assumed to be very long (TR >> T1). The theoretical calculations were confirmed with in vitro and in vivo experiments. For in vitro experiments we used samples with different T2 values using various concentrations of super paramagnetic iron oxide (SPIO) and for in vivo experiments we used an animal model of prostate cancer. Results: CNR was maximized by selecting the optimum TE for a multi-echo spin-echo (MESE) pulse sequence based on theoretical predictions. MR images of prostate cancer at 3T were obtained and showed maximum CNR at the predicted TE. Conclusions: It was possible to maximize CNR of prostate tumour by selecting the optimal TE based on simple theoretical calculations. The proposed method can be applied to other pulse sequences and tissues. It can be applied to any MRI system at any magnetic field. However the method requires knowledge of T2 relaxation times.

Computed high b-value diffusion-weighted imaging improves lesion contrast and conspicuity in prostate cancer.

To evaluate whether very high b-value computed diffusion-weighted imaging (cDWI) is able to provide better contrast between the foci of prostate cancer and background tissue than the standard apparent diffusion coefficient (ADC) map, and whether this improved contrast could be used to improve the tumor detection. Very high b-value cDWI series up to b4000 were created for 14 patients with high-grade prostate cancer. Contrast-to-noise ratios (CNRs) and CNR-to-ADC ratios were calculated. Three blinded readers also assessed the tumor conspicuity on a standard five-point scale. The tumor CNR increased with increasing b-values in all the patients up to a maximum average CNR of 75.1 for a b-value of 4000 (average CNR for the ADC maps: 10.0). CNR/ADC ratios were higher than 1 (indicating higher CNR than respective ADC) for cDWI of 1500 and higher, with a maximum of 6.5 for cDWI4000. The average subjective tumor conspicuity scores for cDWI2000, 3000 and 4000 were significantly higher than that of the ADC (4.0): 4.5 (P=0.018), 4.5 (P=0.017) and 4.6 (P=0.012). cDWI is able to provide better contrast between the foci of prostate cancer and background tissue compared with a standard ADC map. This resulted in improved subjective tumor conspicuity.