Change In Contrast-to-noise Ratio Research Articles

Eigenbin compression for reducing photon-counting CT data size.

Photon-counting CT (PCCT) systems acquire multiple spectral measurements at high spatial resolution, providing numerous image quality benefits while also increasing the amount of data that must be transferred through the gantry slip ring. This study proposes a lossy method to compress photon-counting CT data using eigenvector analysis, with the goal of providing image quality sufficient for applications that require a rapid initial reconstruction, such as to confirm anatomical coverage, scan quality, and to support automated advanced applications. The eigenbin compression method was experimentally evaluated on a clinical silicon PCCT prototype system. The proposed eigenbin method performs principal component analysis (PCA) on a set of PCCT calibration measurements. PCA finds the orthogonal axes or eigenvectors, which capture the maximum variance in the N dimensional photon-count data space, where N is the number of acquired energy bins. To reduce the dimensionality of the PCCT data, the data are linearly transformed into a lower dimensional space spanned by the M<N eigenvectors with highest eigenvalues (i.e., the vectors that account for most of the information in the data). Only M coefficients are then transferred per measurement, which we term eigenbin values. After transmission, the original N energy-bin measurements are estimated as a linear combination of the M eigenvectors. Two versions of the eigenbin method were investigated: pixel-specific and pixel-general. The pixel-specific eigenbin method determines eigenvectors for each individual detector pixel, while the more practically realizable pixel-general eigenbin method finds one set of eigenvectors for the entire detector array. The eigenbin method was experimentally evaluated by scanning a 20cm diameter Gammex Multienergy phantom with different material inserts on a clinical silicon-based PCCT prototype. The method was evaluated with the number of eigenbins varied between two and four. In each case, the eigenbins were used to estimate the original 8-bin data, after which material decomposition was performed. The mean, standard deviation, and contrast-to-noise ratio (CNR) of values in the reconstructed basis and virtual monoenergetic images (VMI) were compared for the original 8-bin data and for the eigenbin data. The pixel-specific eigenbin method reduced photon-counting CT data size by a factor of four with<5% change in mean values and a small noise penalty (mean change in noise of<12%, maximum change in noise of 20% for basis images). The pixel-general eigenbin compression method reduced data size by a factor of 2.67 with<5% change in mean values and a less than 10% noise penalty in the basis images (average noise penalty≤5%). The noise penalty and errors were less for the VMIs than for the basis images, resulting in<5% change in CNR in the VMIs. The eigenbin compression method reduced photon-counting CT data size by a factor of two to four with less than 5% change in mean values, noise penalty of less than 10%-20%, and change in CNR ranging from 15% decrease to 24% increase. Eigenbin compression reduces the data transfer time and storage space of photon-counting CT data for applications that require rapid initial reconstructions.

Can magnetic resonance imaging after cranioplasty using titanium mesh detect brain tumors?

This study determined the dependence of the concentration and position of contrast-enhanced tumors on the radio frequency (RF)-shielding effect of titanium mesh using the contrast-to-noise ratio (CNR) in magnetic resonance imaging (MRI). A phantom was constructed by filling a plastic container with manganese chloride tetrahydrate and agar. Four cellophane cylindrical containers were arranged from the end of the plastic container, and the brain tumor model was filled with gadobutrol diluted with NaCl, with molarity values of 0.2-1.0mmol/L. The titanium mesh board was set on the left side of the phantom. Images were acquired using a 1.5-T MRI as well as two-dimensional spin-echo (2D SE) and three-dimensional fast spoiled gradient echo (3D FSPGR) sequences. CNR was calculated using the signal intensity values of the tumor model, surrounding area of the brain model, and background noise. Furthermore, the fractional change in CNR was calculated using values of CNR with and without the mesh. Moreover, a profile of CNR was created. The fractional change in CNR decreased at the brain tumor positions present near the mesh and at a contrast medium concentration of approximately ≤ 0.5mmol/L in 2D SE and ≤ 0.25mmol/L in 3D FSPGR. According to the CNR profiles, directly under the mesh, almost all contrast concentrations in 2D SE was unrecognizable; however, at a concentration of ≥ 0.5 mmol/L in 3D FSPGR was recognizable.

Image Quality of Submillimeter High-Spatial-Resolution 2D Late Gadolinium-enhanced Images in Cardiac MRI: A Feasibility Study.

To evaluate the image quality of high-spatial-resolution two-dimensional (2D) late gadolinium enhancement (LGE) cardiac MRI compared with conventional normal-resolution LGE MRI. This prospective study included participants suspected of having cardiomyopathy who underwent cardiac MRI between March 2021 and December 2021. Normal-resolution and high-resolution 2D LGE sequences (inversion recovery [IR] and phase-sensitive inversion recovery [PSIR]) were performed at 3 T. Resolution was compared between normal-resolution and high-resolution images obtained in a quality assurance phantom. In vivo image quality and resolution were evaluated qualitatively using a five-point scoring system. Receiver operating characteristic curve analysis was used for LGE detection performance. Border sharpness was assessed with profile curve measurement. The contrast-to-noise ratio (CNR) between hyperenhancement and remote myocardium and LGE detection performance were calculated using normal-resolution IR images as the reference. In total, 120 participants were evaluated (mean age, 56 years ± 17 [SD]; 72 men). Features smaller than 1 mm were detectable only on high-resolution images of the phantom. In vivo, the image resolution score with high-resolution LGE was 4.14-4.24, which was higher than the normal-resolution LGE reference score of 2.99 (P < .05). Border sharpness was higher in high-resolution images (P < .001). Receiver operating characteristic curve analysis revealed no evidence of a difference in LGE detection between normal-resolution and high-resolution images. There was also no evidence of a change in CNR of LGE in IR and PSIR magnitude compared with reference images. Comparison of image quality in 2D high-resolution and normal-resolution LGE cardiac MRI demonstrated the highest resolution for high-resolution IR and high-resolution PSIR magnitude sequences.Keywords: Cartilage Imaging, MRI, Cardiac, Heart, Imaging Sequences, Comparative Studies Supplemental material is available for this article. © RSNA, 2022.

Abstract 2454: Imaging pancreatic ductal adenocarcinoma using a zinc-sensitive MRI contrast agent: A novel method to detect early-stage PDAC lesions

Abstract Background: Zinc content and its flux from the exocrine pancreas are both novel candidates for molecular imaging of pancreatic ductal adenocarcinoma (PDAC) due to the markedly dysregulated homeostasis in PDAC lesions. Here, we introduce the use of a Gd-based zinc probe (GdL) to monitor stimulated exocrine function in the healthy and PDAC bearing mouse pancreas by MRI. Methods: Male adult mice were implanted with syngeneic PDAC cells into the pancreas and allowed to form PDAC for 1 and 2 weeks. Healthy mice were used as controls. Mice were fasted overnight and imaged in a 4.7 T scanner. Two 2D T1-weighted gradient echo scans were obtained as baseline (TE/TR = 2.9/125 ms, Avg = 4). Mice then received either 1) 0.07mmol/kg GdL (i.v.) plus 10 ug/kg caerulein (i.p.), 2) 0.07mmol/kg GdL (i.v.) plus Saline (i.p.), or 3) 0.01 mmol/kg Gd-DOTA (i.v.). Immediately following injections, serial 2D T1-weighted gradient echo scans were obtained for 25 minutes. PDAC mice receiving saline were considered as negative controls. Change in contrast to-noise ratio (CNR) of tumor and pancreas was quantified and reported as a function of time. Tumor and pancreas tissue were then fixed, and histological analysis was done to characterize the expression of zinc transporters in healthy pancreas and PDAC tissues. Results: Secretagogue-stimulated zinc secretion (SSZS) MRI of the exocrine pancreas relies on evoking zinc release from intracellular stores from acinar and ductal cells. After i.p. injection of the secretagogue caerulein in fasted healthy animals, we observed only a small enhancement in the pancreas. However, both groups of animals carrying orthotopically implanted PDAC cells (1-wk and 2-wks) responded in hyper-secretory fashion. Negative controls (saline group) did not show significant pancreatic or tumor enhancement. Importantly, the effect of caerulein in PDAC animals and the increase in overall pancreatic enhancement were only found in PDAC tumor bearing animals. Dysregulation of zinc trafficking was confirmed by immunohistochemistry staining for the zinc import transporters ZIP3 and ZIP4. These transporters were upregulated only in PDAC-bearing pancreas and the positive staining was concentrated mostly in the tumor parenchyma and gradually dissipated in the surrounding pancreatic tissue. Conclusions: Zinc flux is markedly upregulated in PDAC. By stimulating the natural zinc secretion from exocrine pancreatic cells using an exogenous secretagogue, caerulein, we can non-invasively monitor early malignant transformations in pancreatic parenchyma and tumor cells by MRI with a Gd-based zinc sensitive probe. Citation Format: Mozhdeh Sojoodi, Ian Ramsay, Eric Gale, Stephen C. Barrett, Motaz Qadan, Peter Caravan, Kenneth K. Tanabe, Veronica Clavijo Jordan. Imaging pancreatic ductal adenocarcinoma using a zinc-sensitive MRI contrast agent: A novel method to detect early-stage PDAC lesions [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2454.

Treatment effect of mTOR-inhibition on tissue composition of renal angiomyolipomas in tuberous sclerosis complex (TSC).

PurposeTuberous sclerosis complex (TSC)-associated renal angiomyolipoma (AML) have a high lifetime risk of acute bleeding. MTOR-inhibitors are a promising novel treatment for TSC-AML, however adequate response to therapy can be difficult to assess. Early changes in MRI signal may serve as a novel early indicator for a satisfactory response to mTOR-inhibitor therapy of AML.Materials and methodsThirty-eight patients with the definite diagnosis of tuberous sclerosis receiving everolimus therapy and n = 19 patients without specific therapy were included. 1.5 Tesla MRI was performed including sequences with a selective fat suppression. Patients were investigated prior to the initiation of therapy (baseline) and after <3 months (n = 21 patients), 3 to 6 months (n = 32) and 18 to 24 months (n = 28). Signal and size changes of renal AMLs were assessed at all different timepoints. Signal-to-noise-ratio (SNR), contrast-to-noise-ratio (CNR) and size of angiomyolipomas were evaluated.ResultsSignal changes in 273 AMLs were evaluated. A significant and strong decrease of the CNR of AMLs following the initiation of therapy was measured in the fat-suppressed MR sequence at all time points, compared to the baseline: From 7.41±6.98 to 3.84±6.25 (p ≤ 0.05p = 0.002), 3.36±6.93 (p<0.0001), and 2.50±6.68 (p<0.0001) after less than 3 months, 3–6 months or 18–24 months of everolimus treatment, respectively. Also, a significant, however less pronounced, reduction of angiomyolipoma size in the different groups was measured (from baseline 2022.2±2657.7 mm2 to 1854.4±1670.9 mm2 (p = 0.009), 1875.5±3190.1 mm2 (p<0.001), and 1365.8 ± 1628.8 mm2 (p<0.0001) after less than 3 months, 3–6 months or 18–24 months of everolimus treatment, respectively). No significant changes in CNR (p>0.05) and size (p>0.05) were measured in the control group.ConclusionmTOR inhibitor therapy in TSC patients results in an early and pronounced fatty transformation of AMLs on MRI. Fatty transformation could represent a novel early indicator of response to therapy in this patient collective.

Quantifying cross-scatter contamination in biplane fluoroscopy motion analysis systems.

Biplane fluoroscopy is used for dynamic in vivo three-dimensional motion analysis of various joints of the body. Cross-scatter between the two fluoroscopy systems may limit tracking accuracy. This study measured the magnitude and effects of cross-scatter in biplane fluoroscopic images. Four cylindrical phantoms of 4-, 6-, 8-, and 10-in. diameter were imaged at varying kVp levels to determine the cross-scatter fraction and contrast-to-noise ratio (CNR). Monte Carlo simulations quantified the effect of the gantry angle on the cross-scatter fraction. A cadaver foot with implanted beads was also imaged. The effect of cross-scatter on marker-based tracking accuracy was investigated. Results demonstrated that the cross-scatter fraction varied from 0.15 for the 4-in. cylinder to 0.89 for the 10-in. cylinder when averaged across kVp. The average change in CNR due to cross-scatter ranged from 5% to 36% CNR decreases for the 4- and 10-in. cylinders, respectively. In simulations, the cross-scatter fraction increased with the gantry angle for the 8- and 10-in. cylinders. Cross-scatter significantly increased static-tracking error by 15%, 25%, and 38% for the 6-, 8-, and 10-in. phantoms, respectively, with no significant effect for the foot specimen. The results demonstrated submillimeter marker-based tracking for a range of phantom sizes, despite cross-scatter degradation.

TU‐G‐204‐04: A Unified Strategy for Bi‐Factorial Optimization of Radiation Dose and Contrast Dose in CT Imaging

Purpose:To substantiate the interdependency of contrast dose, radiation dose, and image quality in CT towards the patient‐ specific optimization of the imaging protocolsMethods:The study deployed two phantom platforms. A variable sized (12, 18, 23, 30, 37 cm) phantom (Mercury‐3.0) containing an iodinated insert (8.5 mgI/ml) was imaged on a representative CT scanner at multiple CTDI values (0.7–22.6 mGy). The contrast and noise were measured from the reconstructed images for each phantom diameter. Linearly related to iodine‐concentration, contrast‐to‐noise ratio (CNR), were calculated for 16 iodine‐concentration levels (0–8.5 mgI/ml). The analysis was extended to a recently developed suit of 58 virtual human models (5D XCAT) with added contrast dynamics. Emulating a contrast‐enhanced abdominal image procedure and targeting a peak‐enhancement in aorta, each XCAT phantom was “imaged” using a simulation platform (CatSim, GE). 3D surfaces for each patient/size established the relationship between iodine‐concentration, dose, and CNR. The ratios of change in iodine‐concentration versus dose (IDR) to yield a constant change in CNR were calculated for each patient size.Results:Mercury phantom results show the image‐quality size‐ dependence on CTDI and IC levels. For desired image‐quality values, the iso‐contour‐lines reflect the trade off between contrast‐material and radiation doses. For a fixed iodine‐concentration (4 mgI/mL), the IDR values for low (1.4 mGy) and high (11.5 mGy) dose levels were 1.02, 1.07, 1.19, 1.65, 1.54, and 3.14, 3.12, 3.52, 3.76, 4.06, respectively across five sizes. The simulation data from XCAT models confirmed the empirical results from Mercury phantom.Conclusion:The iodine‐concentration, image quality, and radiation dose are interdependent. The understanding of the relationships between iodine‐concentration, image quality, and radiation dose will allow for a more comprehensive optimization of CT imaging devices and techniques, providing the methodology to balance iodine‐concentration and dose based on patient's attributes.

SU‐E‐I‐52: Improvement in CT Contrast‐To‐Noise Ratio in Low Contrast Spherical Simulated Liver Lesions Using Iterative Reconstruction

Purpose: Contrast‐to‐Noise ratio (CNR) is one measure to assess image quality and lesion detectability for CT exams. The purpose of this study is to calculate the change in CNR between standard filtered back‐projection (FBP) and sinogram‐affirmed iterative reconstruction (SAFIRE) by using an anthropomorphic phantom with spherical simulated liver lesions. Methods: An anthropomorphic phantom with embedded spherical liver lesions was custom‐designed to assess low contrast lesion detection at different CT doses and reconstruction techniques. This phantom consists of 36 spherical lesions with 3 different sizes (5mm, 10mm, and 15mm). Each size has three different contrast levels. All spherical lesions were embedded non‐uniformly to minimize the memory bias for a concurrent human observer study. Phantom was scanned with a MDCT (Siemens Definition Flash) at 4 dose levels and images were reconstructed with both FBP and SAFIRE using strength setting 3. CNR was computed as the ratio of the difference of the mean CT number at the center of the lesion and the liver background to the standard deviation of the CT numbers from the liver background. CNR was evaluated for the each lesion size at the center slice that intersected the middle of the lesion to minimize the error from the partial volume effect. Results: Averaged across all lesion sizes and the contrast levels (vs. the liver background), the CNR improvement from FBP to SAFIRE (strength 3) was 34% ±10% (mean ± standard deviation) at 50mAs,(p&lt;0.0001), 33%±11% at 100mAs (p&lt;0.0002), 36% ± 9% at 150mAs (p&lt;0.0001) and 36% ± 7% at 200mAs (p&lt;0.0003). Noise reduction from SAFIRE contributed almost entirely to the CNR improvement. Conclusion: Iterative reconstruction (SAFIRE) improved CNR of spherical low‐contrast liver lesions, but almost entirely due to noise reduction, with little improvement in lesion contrast. The overall CNR improvement was uniform for each dose level tested. Dr. Herts and Dr. Baker are funded by Siemens Healthcare for research in the field of abdominal CT imaging.

Efficacy and Safety of Gadobutrol (1.0 M) versus Gadopentetate Dimeglumine (.5 M) for Enhanced Mri of Cns Lesions: A Phase Iii, Multicenter, Single-blind, Randomized Study in Chinese Patients

The aim of this study was to compare the efficacy and safety of macrocyclic gadobutrol (1.0 M) with linear gadopentetate dimeglumine (0.5 M) for contrast-enhanced magnetic resonance imaging (MRI) of central nervous system (CNS) lesions in Chinese patients (N = 147) with known or suspected CNS lesions, who were enrolled in this single-blind, randomized, parallel-group study. Three blinded independent readers evaluated all efficacy variables. The primary efficacy variable was the difference between the two agents for the change in contrast-to-noise ratio (CNR) between non-enhanced and contrast-enhanced scans of lesions. Secondary outcomes included mean change in number of lesions detected before and after contrast enhancement, diagnostic confidence, and safety and tolerability parameters. Gadobutrol was non-inferior to gadopentetate dimeglumine in respect to the difference in the mean change in CNR (6.94; 95% confidence interval [CI] lower limit: -3.90; predefined maximum 95% CI lower limit: -6.52). The mean change in the number of CNS lesions detected was greater with gadobutrol versus gadopentetate dimeglumine (1.2 vs. 0.2 lesions). Diagnostic confidence was classified as ‘high’ for more patients with gadobutrol versus gadopentetate dimeglumine by the investigators (58.8% vs. 55.4%) and by the three blinded readers (63.6% vs. 55.7%, 23.7% vs. 18.0% and 81.7% vs. 81.0%). Both agents were well tolerated by participating patients. We concluded that in Chinese patients with CNS lesions, gadobutrol (1.0 M) was as effective and well tolerated in contrast-enhanced MRI as gadopentetate dimeglumine (0.5 M). Gadobutrol provided improved visualization of CNS lesions compared with gadopentetate dimeglumine, with a comparable tolerability profile.

Monitoring therapeutic responses of primary bone tumors by diffusion-weighted image: initial results

The purpose of our study was to investigate whether quantitative diffusion-weighted images (DWI) were useful for monitoring the therapeutic response of primary bone tumors. We encountered 18 osteogenic and Ewing sarcomas. Magnetic resonance (MR) images were performed in all patients before and after therapy. We measured the apparent diffusion coefficient (ADC) values, contrast-to-noise ratio (CNR), and tumor volume of the bone tumors pre- and posttreatment. We determined change in ADC value, change in CNR on T2-weighted images (T2WI), change in CNR on gadopentetate dimeglumine (Gd)-T1-weighted images (Gd-T1WI), and change in tumor volume. The bone tumors were divided into two groups: group A was comprised of tumors with less than 90% necrosis after treatment and group B of tumors at least with 90%. Changes in ADC value, tumor volume, and CNR were compared between the groups. Change in the ADC value was statistically greater in group B than that in the group A (p = 0.003). There was no significant difference in the changes in CNR on T2WI (p = 0.683), in CNR on Gd-T1WI (p = 0.763), and tumor volume (p = 0.065). The ADC value on DWI is a promising tool for monitoring the therapeutic response of primary bone sarcomas.

TU‐D‐I‐611‐06: A Direct, Empirical Method for X‐Ray Scatter Correction in Digital Radiography and Cone‐Beam CT

Purpose: X‐ray scatter poses a severe physical limitation to image quality in cone‐beam CT (CBCT), resulting in contrast reduction, image artifacts, and lack of CT number accuracy. We report and demonstrate the performance of a novel scatter correction method in which scatter fluence is estimated directly in each projection from pixel values at the edge of the detector behind the collimator leaves. Method and Materials: The algorithm operates on the assumption that signal behind the collimator leaves is attributable to x‐ray scatter. The 2D scatter fluence is estimated by interpolating between pixel values measured along the top and bottom edges of the detector behind the collimator leaves. The resulting scatter fluence is subtracted from each projection to yield primary‐only images for CBCT reconstruction. Performance was investigated in phantom experiments on an experimental CBCT benchtop, and the effect on image quality was demonstrated in patient images (head, chest, and pelvis sites) obtained on a preclinical system for CBCT‐guided radiation therapy. Results: The algorithm provides significant reduction in scatter artifacts without compromise in contrast‐to‐noise ratio (CNR) — e.g., Head: cupping reduced from 10% to 2%, while breast‐to‐water CNR improved from 5.2% to 7.8%; Body: cupping reduced from 42% to 26% without change in CNR. Patient images demonstrate increased uniformity, accuracy, and contrast, with slightly increased noise (net increase in CNR) in all of the sites investigated. Qualitative evaluation illustrates that soft‐tissue structures that are otherwise undetectable are clearly delineated in scatter‐corrected reconstructions. Conclusion: The algorithm provides a robust method for x‐ray scatter fluence estimation and correction in CBCT. Operating from a single assumption without prior information, analytical modeling, or Monte Carlo, the technique is easily incorporated as a preprocessing step in CBCT reconstruction. Quantitative evaluation in phantoms and pre‐clinical evaluation in patients demonstrates significant artifact reduction without degradation in CNR.

Liver tumors: utility of characterization at dual-frequency US.

To evaluate the potential utility of a technique for analysis of ultrasonographic (US) images obtained at two center frequencies in a phantom model and in a clinical study of liver tumors. A US phantom was built that contained target regions with polystyrene scatterers both smaller and larger than scatterers in the background material. High- and low-frequency US images of target regions were obtained, and changes in the contrast-to-noise ratio (CNR) of the targets relative to the background were determined. In a clinical evaluation, 12 hemangiomas, 13 liver metastases, one adenoma, and two hepatomas were evaluated in a similar manner, and the results were correlated with the histologic findings in resected lesions. For targets containing scatterers smaller than those in the background, there was an increase in CNR of higher frequency images. The converse was true for target regions having scatterers larger than those in the background. Liver metastases generally showed an increase in CNR of higher frequency images, whereas hemangiomas generally showed somewhat decreased CNR of higher frequency images, differing significantly from metastases (P < .01-.001). Changes in CNRs of relatively high- and low-frequency US images may give useful information on the frequency dependence of backscattering, which is descriptive of the histologic findings in lesions and which is not evident with conventional US images.