Validation of a New Scintillating Fiber Dosimeter for Radiation Dose Quality Control in Computed Tomography.

(1) Background: The IVIscan is a commercially available scintillating fiber detector designed for quality assurance and in vivo dosimetry in computed tomography (CT). In this work, we investigated the performance of the IVIscan scintillator and associated method in a wide range of beam width from three CT manufacturers and compared it to a CT chamber designed for Computed Tomography Dose Index (CTDI) measurements. (2) Methods: We measured weighted CTDI (CTDIw) with each detector in accordance with the requirements of regulatory tests and international recommendations for the minimum, maximum and the most used beam width in clinic and investigated the accuracy of the IVIscan system based on the assessment of the CTDIw deviation from the CT chamber. We also investigated the IVIscan accuracy for the whole range of the CT scans kV. (3) Results: We found excellent agreement between the IVIscan scintillator and the CT chamber for the whole range of beam widths and kV, especially for wide beams used on recent technology of CT scans. (4) Conclusions: These findings highlight that the IVIscan scintillator is a relevant detector for CT radiation dose assessments, and the method associated with calculating the CTDIw saves a significant amount of time and effort when performing tests, especially with regard to new CT technologies.

Wide-Band Wide-Beam Circularly-Polarized Slot-Coupled Antenna for Wide-Angle Beam Scanning Arrays.

The design of a wide-band wide-beam circularly-polarized slot-coupled (WWCS) radiating element for wide-angle scanning arrays (WASAs) is addressed. The WWCS radiator exploits a simple geometry composed of a primary (driven) and a secondary (passive) element to generate wide-beam patterns with rotational symmetry and high polarization purity. The synthesis was carried out by means of a customized version of the System-by-Design (SbD) method to derive a WWCS radiator with circular polarization (CP) and wide-band impedance matching. The results of the numerical assessment, along with a tolerance analysis, confirm that the synthesized WWCS radiating element is a competitive solution for the implementation of large WASAs. More specifically, a representative design working at f0=2.45 [GHz] is shown having fractional bandwidth FBW≃15%, half-power beam-width HPBWf0≃180 [deg] in all elevation planes, and high polarization purity with broadside axial ratio ARf0=3.2 [dB] and cross-polar discrimination XPDf0=15 [dB]. Finally, the experimental assessment, carried out on a PCB-manufactured prototype, verifies the wide-band and wide-beam features of the designed WWCS radiator.

3D Meta-Prisms for Versatile Beam Steering by Hybridizing Plasmonic and Diffractive Effect in the Broadband Visible Regime.

As two independent optical sub-fields, diffraction optics and plasmonics both have been used for wavefront shaping and beam steering. However, the two separate concepts have always been developing as two parallel directions, which have not met for studying their structural hybridization to discover new potentials. For instance of the flat metasurfaces, even though the geometric parameters including shape, size, and periodicity have been studied, it remains mostly unexplored for the 3D spatial height variation. Here, a new type of all-metallic 3D meta-prism is proposed and experimentally demonstrated by hybridizing the localized surface plasmonic resonances (LSPR) and the blazed grating diffraction, which enables strong polarization-dependent behaviors to steer broadband visible light to drastically inverse directions. The nanofabrication of 3D meta-prism is achieved by nanostencil lithography with electron-beam evaporation. Such meta-prism could also enable to split different visible light (green, blue, and red) with high-efficiency contrast (≈10). By the mirror-symmetry arrangement, a multifunctional surface is demonstrated with polarization-/wavelength-multiplexing wavefront-shaping functions (concave, convex, or flat mirror). This unique 3D meta-prism enjoys great simplicity and versatility in broadband beam steering through the incorporation of plasmonic and diffractive effects and can be utilized in various applications including dichroic-prism splitters, multifunctional meta-mirrors, etc.

Technical Note: Using linear and polynomial approximations to correct IEC CTDI measurements for a wide-beam CT scanner.

PURPOSE: To investigate a feasible correction to align the international electrotechnical commission (IEC) computed tomography dose index (CTDI) measurement with other approaches for an accurate measure of radiation output. METHODS: Radiation dose measurements were performed in a GE 256-slice CT scanner using three methods. The first method used a 0.6 cc Farmer chamber to measure peak dose and then to calculate dose length integral (DLI). The second method integrated dose profiles with a pencil chamber over 600 mm for both body and head phantoms. Both methods achieved scatter equilibrium using a 600 mm long body and head phantom. The third method followed IEC recommendations by adjusting traditional CTDI with beam width. We performed measurements using polymethyl methacrylate (PMMA) 32 cm diameter body and 16 cm diameter head phantoms, combining with various available bowtie filters and at different kV settings. Correction factors using linear or polynomial functions were developed based on these measurements. RESULTS: CTDI measurements using the DLI method and direct integration (DLP) method align with each other with an error of <6.7% for the body phantom, and 6.9% for head phantom respectively. The IEC method underestimates radiation dose for body and head phantoms relative to the DLI, with an error range from 8.9% to 19.4%, depending on the phantom and bowtie filter. A correction factor of 0.15 (15%) could be used for body and head phantom measurements with large body, head and pediatric head bowtie filters. While for body phantom with medium filter and head phantom with small body filter which are not routinely used for CTDI measurements, a correction factor of 0.30 (30%) could be used. The proposed correction factors are validated using various kV and filter combinations. Compared to a linear approximation, a polynomial correction is better at adjusting the IEC measurements, with an error of 5.2%. We found that the a1 coefficient of the polynomial correction is approximately equal to Aeq obtained from DLI measurements for all cases studied, with an average percent difference of 6.7%. CONCLUSION: Both linear and polynomial approximations can be used to correct the IEC measurements, aligning them with the direct integration of dose profiles or the point detector method of CT dosimetry on a 256 slice GE Revolution scanner. Using a polynomial correction may potentially bypass the need for an elongated phantom in the DLI method since the a1 coefficients are approximately equal to Aeq obtained from the DLI method.

Wideband and Wide Beam Polyvinylidene Difluoride (PVDF) Acoustic Transducer for Broadband Underwater Communications.

The advances in wireless communications are still very limited when intended to be used on Underwater Communication Systems mainly due to the adverse proprieties of the submarine channel to the acoustic and radio frequency (RF) waves propagation. This work describes the development and characterization of a polyvinylidene difluoride ultrasound transducer to be used as an emitter in underwater wireless communications. The transducer has a beam up to 10° × 70° degrees and a usable frequency band up to 1 MHz. The transducer was designed using Finite Elements Methods and compared with real measurements. Pool trials show a transmitting voltage response (TVR) of approximately 150 dB re µPa/V@1 m from 750 kHz to 1 MHz. Sea trials were carried in Ria Formosa, Faro (Portugal) over a 15 m source-receiver communication link. All the signals were successfully detected by cross-correlation using 10 chirp signals between 10 to 900 kHz.

Radiation Dose Measurements in a 256-Slice Computed Tomography Scanner.

PURPOSE: The purpose of this study is to compare computed tomography (CT) radiation dose measurement methods proposed by TG111, International Electrotechnical Commission (IEC), and a direct dose profile integral (DPI) measurement method. METHODS: Pencil and Farmer ion chambers are used for integrating dose profiles at different beam widths in a 60 cm long body phantom. Resulting DPI is used to calculate CT dose index (CTDI) at each beam width. Measurements are also done for a pencil chamber inserted into a 15 cm body phantom at the reference beam width. The reference measurement is scaled with pencil chamber measurements in air at different beam widths, according to the IEC approach. Finally, point dose measurements are done with a Farmer chamber under equilibrium conditions according to the TG111 method. All CTDIs calculated from measured data are compared to the scanner displayed CTDIs. RESULTS: Calculated CTDIs, at different beam widths, using the IEC approach are within 20% of CTDIs calculated from DPI measurements in a 60 cm long body phantom. Dose Length Integral (DLI) obtained from TG111 method is close to the results obtained from DPI measurements. Scanner displayed CTDIs are lower than all measured values by up to 38% at the techniques used. CONCLUSION: Although the IEC method is the easiest to use compared to the TG111 and direct DPI measurement method, it underestimates dose indices by about 20%. CTDIs displayed on the GE scanner are lower than those measured in this study by up to 38%.

Reducing radiation to patients and improving image quality in a real-world nuclear cardiology laboratory.

In part because of aging equipment and reduced reimbursement for imaging services in the last several years, nuclear cardiologists who remain in private practice face challenges in maintaining high quality and in reducing radiation exposure to patients. We review patient-centered approaches and affordable software solutions employed in our practice combined with supine-prone myocardial perfusion imaging to achieve increased interpretive confidence with reduced radiation exposure to patients.