Physical and dosimetric characterisation of different Contrast-Enhanced digital mammographic systems: A multicentric study.

PURPOSE: Contrast-enhanced digital mammography (CEDM) is a relatively new imaging technique recombining low- and high-energy mammograms to emphasise iodine contrast. This work aims to perform a multicentric physical and dosimetric characterisation of four state-of-the-art CEDM systems. METHODS: We evaluated tube output, half-value-layer (HVL) for low- and high-energy and average glandular dose (AGD) in a wide range of equivalent breast thicknesses. CIRS phantom 022 was used to estimate the overall performance of a CEDM examination in the subtracted image in terms of the iodine difference signal (S). To calculate dosimetric impact of CEDM examination, we collected 4542 acquisitions on patients. RESULTS: Even if CEDM acquisition strategies differ, all the systems presented a linear behaviour between S and iodine concentration. The curve fit slopes expressed in PV/mg/cm2 were in the range [92-97] for Fujifilm, [31-32] for GE Healthcare, [35-36] for Hologic, and [114-130] for IMS. Dosimetric data from patients were matched with AGD values calculated using equivalent PMMA thicknesses. Fujifilm exhibited the lowest values, while GE Healthcare showed the highest. CONCLUSION: The subtracted image showed the ability of all the systems to give important information about the linearity of the signal with the iodine concentrations. All the patient-collected doses were under the AGD EUREF 2D Acceptable limit, except for patients with thicknesses ≤35 mm belonging to GE Healthcare and Hologic, which were slightly over. This work demonstrates the importance of testing each CEDM system to know how it performs regarding dose and the relationship between PV and iodine concentration.

Lung dual energy CT: Impact of different technological solutions on quantitative analysis.

PURPOSE: To evaluated the accuracy of spectral parameters quantification of four different CT scanners in dual energy examinations of the lung using a dedicated phantom. METHOD: Measurements were made with different technologies of the same vendor: one dual source CT scanner (DSCT), one TwinBeam (i.e. split filter) and two sequential acquisition single source scanners (SSCT). Angular separation of Calcium and Iodine signals were calculated from scatter plots of low-kVp versus high-kVp HUs. Electron density (ρe), effective atomic number (Zeff) and Iodine concentration (Iconc) were measured using Syngo.via software. Accuracy (A) of ρe, Zeff and Iconc was evaluated as the absolute percentage difference (D%) between reference values and measured ones, while precision (P) was evaluated as the variability σ obtained by repeating the measurement with different acquisition/reconstruction settings. RESULTS: Angular separation was significantly larger for DSCT (α = 9.7°) and for sequential SSCT (α = 9.9°) systems. TwinBeam was less performing in material separation (α = 5.0°). The lowest average A was observed for TwinBeam (Aρe = [4.7 ± 1.0], AZ = [9.1 ± 3.1], AIconc = [19.4 ± 4.4]), while the best average A was obtained for Flash (Aρe = [1.8 ± 0.4], AZ = [3.5 ± 0.7], AIconc = [7.3 ± 1.8]). TwinBeam presented inferior average P (Pρe = [0.6 ± 0.1], PZ = [1.1 ± 0.2], PIconc = [10.9 ± 4.9]), while other technologies demonstrate a comparable average. CONCLUSIONS: Different technologies performed material separation and spectral parameter quantification with different degrees of accuracy and precision. DSCT performed better while TwinBeam demonstrated not excellent performance. Iodine concentration measurements exhibited high variability due to low Iodine absolute content in lung nodules, thus limiting its clinical usefulness in pulmonary applications.

How tissue T1-variability influences DCE-MRI perfusion parameters estimation of recurrent high-grade glioma after surgery followed by radiochemotherapy.

BACKGROUND: Quantification of dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) kinetic parameters (KPs) requires a determination of native tissue T1. Two approaches are adopted: (i) tissue T1-maps are acquired; and (ii) an a priori T1 value (fT1) is fixed for all patients (fT1-approach). Although it is more attractive, the fT1-approach might bias the results of KP calculations due to tissue T1 variability. PURPOSE: To quantify the tissue T1 variability of recurrent high-grade glioma (HGG) and the error in KP estimation when the fT1-approach is adopted. MATERIAL AND METHODS: We reviewed the postoperative MRI scans of 28 patients with recurrent HGG after radiochemotherapy. MRI study included T1-maps from multiple-dynamic multiple-echo imaging, DCE-MRI, and contrast enhanced T1-weighted images. KPs were calculated using T1-map and fT1-approach. RESULTS: The tissue T1 variability of recurrent HGG was relevant. The absolute error in KP estimation, as a function of the deviation of fT1 from the true value, was 8% every 100 ms. The difference between the KPs obtained with fT1-approach from fT1 values of 1300, 1390, and 1500 ms and their reference values were mostly within the 95% confidence interval (± 1.96 standard deviation). Conversely, using fT1 values of 900, 1200, 1600, and 1900 ms causes a significant error in KP estimation (P<0.05). CONCLUSION: Recurrent HGG is characterized by a substantial T1 variability. Although the fT1-approach does not account for this variability, it results in a minor effect on the KP estimations provided the fT1 value is in the range of 1300-1500 ms.

Characterization of GE discovery IGS 740 angiography system by means of channelized Hotelling observer (CHO).

The aim of the study is to use the well-known channelized Hotelling observer model (CHO) to characterize a recently installed angiography system (GE Discovery IGS 740) using sets of images of a contrast-detail phantom acquired with clinical protocols. A Leeds TO10 phantom was used. The phantom has 108 details: 12 diameters (size range: 0.25 mm-11 mm), each with nine contrasts (declared range: 0.012-0.930 at 70 kVp 1.00 with 1 mm Cu filtration). TO10 has been imaged between two 10 cm thick homogeneous solid water slabs. Two FOVs (32 cm and 20 cm) were used. Fluoroscopy images were taken using an abdominal protocol at two different frame rates (15 fps and 7.5 fps) and at two dose levels (low and normal); cineangiography images were acquired using an abdominal protocol at 15 fps at two dose levels (low and normal). A 40 Gabor channels CHO with internal noise was used. Human observers' studies were carried out to tune the internal noise parameter and to validate the model observer. Contrast-detail curves were obtained from the CHO output using a visibility threshold of 75% and fitted with Rose's model theory in order to characterize the angiography system. Wilcoxon rank-sum tests were performed to investigate possible differences among the different sets of images. The CHO can distinguish between the two dose levels (p -values < 0.002), while FOV and frame rate do not affect the contrast-detail curves significantly. It is important to note that the CHO does not find statistically significant differences between a fluoroscopy with FOV = 20 cm at normal dose level (17.6 mGy min-1) and a cineangiography with FOV = 32 cm low dose level (42.1 mGy min-1). This result can lead to a dose reduction of about 70% for our specific task (i.e. a static, disc shaped object at known location in homogeneous field). Given their stability in comparison to human observers, model observers provide an effective tool for image quality evaluation.

Radiation dose reduction in myocardial perfusion imaging single-photon emission computed tomography/computed tomography using a dose-tracking software.

OBJECTIVE: We describe our experience with a dose-tracking software (Radimetrics) that was used to optimize, from a dosimetric point of view, the single-photon emission computed tomography/computed tomography protocols used in myocardial perfusion imaging. PATIENTS AND METHODS: We extracted and assessed the major dosimetric indices as the administered activity, the computed tomography dose index, the dose length product and the size-specific dose estimates for a large sample of patients before and after an optimization process. We also evaluated both the effective and the equivalent dose to organs for all the procedures. RESULTS: We achieved a reduction in administered activity by 17.8 and 4.5% for 2- and 1-day protocols, respectively; moreover size-specific dose estimates related to a single computed tomography acquisition was reduced by 50%. The organs that received the highest equivalent dose were the heart and the breast, and with the new protocols, these values were almost halved.The average single-photon emission computed tomography/computed tomography myocardial perfusion imaging effective dose decreased from 21.9±2.5 to 15.6±1.4 mSv for the 2-day protocol and from 17.8±1.7 to 13.6±1.5 mSv for the 1-day protocol. This meant that with a simple but targeted action on acquisition protocols, it was possible to achieve considerable dosimetric reduction.The adoption of a dose-tracking software represented an easy approach to optimization. Furthermore, we could easily calculate the main dosimetric indices and check their trends day by day to perform the necessary corrective actions in real timeVideo abstract: http://links.lww.com/NMC/A135.

Development and Validation of a High-Pressure Liquid Chromatography Method for the Determination of Chemical Purity and Radiochemical Purity of a [68Ga]-Labeled Glu-Urea-Lys(Ahx)-HBED-CC (Positron Emission Tomography) Tracer.

Background: Prostate-specific membrane antigen (PSMA) has gained high attention as a useful biomarker in the imaging evaluation of prostate cancer with positron emission tomography (PET) during recent years. [68Ga]-labeled Glu-urea-Lys(Ahx)-HBED-CC ([68Ga]-PSMA-HBED-CC) is a novel PSMA inhibitor radiotracer which has demonstrated its suitability in detecting prostate cancer. Preparation conditions may influence the quality and in vivo behavior of this tracer, and no standard procedure for the quality control (QC) is available. The aim of this study was to develop a new rapid and simple high-pressure liquid chromatography method of analysis for the routine QCs of [68Ga]-PSMA-HBED-CC to guarantee the high quality of the radiopharmaceutical product before release. Methods: A stepwise approach was used based on the quality by design concept of the International Conference of Harmonisation Q2 (R1) and Q8 (Pharmaceutical Development) guidelines in accordance with the regulations and requirements of European Association of Nuclear Medicine, Society of Nuclear Medicine, International Atomic Energy Agency, World Health Organization, and Italian Association of Nuclear Medicine and Molecular Imaging. The developed analytical test method was validated because a specific monograph in the pharmacopoeia is not available for [68Ga]-PSMA-HBED-CC. Results: The purity and quality of the radiopharmaceutical obtained according to the proposed method resulted high enough to safely administrate it to patients. An excellent linearity was found between 0.8 and 5 µg/mL, with a detection limit of 0.2 µg/mL. Assay imprecision (% CV) was <2%. Conclusions: The developed method to assess the radiochemical and chemical purity of [68Ga]-PSMA-HBED-CC is rapid, accurate, and reproducible, allowing routinely the use of this PET tracer as a diagnostic tool for imaging prostate cancer and also assuring patient safety.

Physical characterization of a new CT iterative reconstruction method operating in sinogram space.

Recently a new iterative reconstruction algorithm named Iterative Reconstruction (SAFIRE) has been released by Siemens. This algorithm works in the raw data domain with noise reduction as main purpose, providing five different strengths. In this study, the effect of SAFIRE on image quality has been investigated using selected phantoms and a comparison with standard filtered back projection (FBP) has been carried out. The following quantitative parameters have been evaluated: image noise, impact of different reconstruction kernels on noise reduction, noise power spectrum (NPS), contrast-to-noise ratio (CNR), spatial resolution, and linearity and accuracy of CT numbers. The influence of strengths on image quality parameters has also been examined. Results show that image noise reduction is independent of reconstruction kernel and strongly related to the strength of SAFIRE applied. The peak of NPS curve for SAFIRE reconstructions is shifted towards low frequencies; this effect is more marked at higher levels of strength. Contrast-to-noise ratio is always improved in SAFIRE reconstruction and increases with higher strength. At different dose levels SAFIRE preserves CT number accuracy, linearity, and spatial resolution, both in transversal and coronal planes. These results confirm that SAFIRE allows for image noise reduction with preserved image quality. First clinical data to validate this phantom analysis and confirm that commercially available iterative algorithms can play an effective role in dose containment.

Physical characteristics of GE Senographe Essential and DS digital mammography detectors.

The purpose of this study was to investigate physical characteristics of two full field digital mammography (FFDM) systems (GE Senographe Essential and DS). Both are indirect conversion (x ray to light) alpha-Si flat panels coupled with a CsI(Tl) scintillator. The examined systems have the same pixel size (100 microm) but a different field of view: a conventional size 23 x 19.2 cm2 and a large field 24 X 30.7 cm2, specifically designed to image large breasts. In the GE Senographe Essential model relevant improvements in flat panel design were implemented and new deposition tools for metal, alpha-Si, and CsI(Tl) were introduced by GE. These changes in detector design are expected to be beneficial for advanced applications such as breast tomosynthesis. The presampling modulation transfer function (MTF), normalized noise power spectrum (NNPS), and detective quantum efficiency (DQE) were measured for a wide range of exposure (25-240 microGy) with a RQA-M2 technique (28 kVp with a Mo/Mo target/filter combination and 2 mm of additional aluminum filtration). At 1, 2, and at 4 lp/mm MTF is equal to 0.9, 0.76, and 0.46 for the conventional field detector and to 0.85, 0.59, and 0.24 for the large field detector. The latter detector exhibits an improved NNPS due to a lower electronic noise and a better DQE that reaches 60%. In addition a contrast-detail analysis was performed with CDMAM 3.4 phantom and CDCOM software: GE Senographe DS showed statistically significant poorer detection ability in comparison with the GE Senographe Essential. These results could have been expected, at least qualitatively, considering the relative DQE of the two systems.

Measurements of metaphase and interphase chromosome aberrations transmitted through early cell replication rounds in human lymphocytes exposed to low-LET protons and high-LET 12C ions.

Inheritable chromosome aberrations (CA) are of concern because cytogenetic damage may trigger the carcinogenic process. Moreover, stability of radiation-induced CA is a prerequisite for meaningful biological dosimetry. CA inheritability arguably depends on the aberration structure, with symmetrical exchanges being favoured over asymmetrical rearrangements, but it is also affected by radiation quality. CA induced by low-LET protons and high-LET 12C ions in G0 peripheral blood lymphocytes were measured in first- , second- and third-generation by combined FISH/harlequin staining of metaphase as well as prematurely condensed interphase chromosomes 1 and 2. As expected, the frequency of non-transmissible (NT) aberrations declined through replication rounds. A radiation-induced arrest occurred prior to first post-irradiation mitosis that prevalently affected aberrant cells. Aberrant cells incurred cycle delays also at subsequent cycles following proton-irradiation but not 12C ion-irradiation. As expected, the frequency of reciprocal translocations remained fairly stable while that of dicentrics was halved at each mitotic round. A significant fraction of complex-type exchanges was found in third-generation cells following both irradiations and appeared to be transmitted relatively more efficiently after protons than 12C ions. A low but stably transmitted frequency of transmissible (T)-type insertions were detected after 12C ions but not after low LET-irradiation. Our data support a differential ability by aberrant cells to progress through post-irradiation mitoses that is influenced by the aberration burden and radiation quality.