Pitch Factor Research Articles

Establishing local Diagnostic Reference Level for Adult Patients in Computed Tomography Examination in Kohgiluyeh and Boyer-Ahmad province

Introduction: Nowadays, the absorbed dose of patients is on the rise due to the widespread use of computed tomography (CT) during the diagnosis process. Patients' doses for similar procedures are very different due to diversity in scanners and protocols. Hence, the purpose of this study was to determine the diagnostic reference levels for routine CT scan procedures in Kohgiluyeh and Boyer-Ahmad province, Iran. Material and Methods: In this study, four common brain, sinus, chest and abdominopelvic procedures (overall 200 scans) in spiral mode were selected in five CT centers of Kohgiluyeh and Boyer-Ahmad province, Iran. Next, the doses were measured in head and body phantom, based on scan parameters of ten patients in each procedure at each centers (200scans). Then, the third quartile of CTDIw was considered as the diagnostic reference dose. Finally, considering the pitch factor and the mean scan length in each protocol, the diagnostic reference level values based on the third quartile of the dose length product (DLP) and volume CTDI (CTDIvol) were determined. Results: The dose reference level values according to CTDIw third quartile in the brain, sinus, chest and abdominopelvic procedures were 39.82, 20.88, 14.10 and 17.07 mGy, respectively. In terms of dose length product, the diagnostic reference level values in the above procedures were determined to be 702.75, 243.90, 422.02, 865.62 mGy.cm, respectively. Conclusion: The DRLs of the CTDIW, DLP and CTDIvol of brain and sinus scans calculated in this study, were comparable to other provinces, national DRL and eight other countries. However, the same quantities for the chest and abdominopelvic scans showed higher values compared to the mentioned studies, suggesting lowering mAs and increasing pitch number for patient’s dose optimization. In some centers to preserve image quality, it is necessary to optimize radiation conditions, especially for chest and abdominopelvic scans.

An elephant herd grey wolf optimization (EHGWO) algorithm for load balancing in cloud

Purpose The advancements in the cloud computing has gained the attention of several researchers to provide on-demand network access to users with shared resources. Cloud computing is important a research direction that can provide platforms and softwares to clients using internet. However, handling huge number of tasks in cloud infrastructure is a complicated task. Thus, it needs a load balancing (LB) method for allocating tasks to virtual machines (VMs) without influencing system performance. This paper aims to develop a technique for LB in cloud using optimization algorithms. Design/methodology/approach This paper proposes a hybrid optimization technique, named elephant herding-based grey wolf optimizer (EHGWO), in the cloud computing model for LB by determining the optimal VMs for executing the reallocated tasks. The proposed EHGWO is derived by incorporating elephant herding optimization (EHO) in grey wolf optimizer (GWO) such that the tasks are allocated to the VM by eliminating the tasks from overloaded VM by maintaining the system performance. Here, the load of physical machine (PM), capacity and load of VM is computed for deciding whether the LB has to be done or not. Moreover, two pick factors, namely, task pick factor (TPF) and VM pick factor (VPF), are considered for choosing the tasks for reallocating them from overloaded VM to underloaded VM. The proposed EHGWO decides the task to be allocated in the VM based on the newly derived fitness functions. Findings The minimum load and makespan obtained in the existing methods, constraint measure based LB (CMLB), fractional dragonfly based LB algorithm (FDLA), EHO, GWO and proposed EHGWO for the maximum number of VMs is illustrated. The proposed EHGWO attained minimum makespan with value 814,264 ns and minimum load with value 0.0221, respectively. Meanwhile, the makespan values attained by existing CMLB, FDLA, EHO, GWO, are 318,6896 ns, 230,9140 ns, 1,804,851 ns and 1,073,863 ns, respectively. The minimum load values computed by existing methods, CMLB, FDLA, EHO, GWO, are 0.0587, 0.026, 0.0248 and 0.0234. On the other hand, the proposed EHGWO with minimum load value is 0.0221. Hence, the proposed EHGWO attains maximum performance as compared to the existing technique. Originality/value This paper illustrates the proposed LB algorithm using EHGWO in a cloud computing model using two pitch factors, named TPF and VPF. For initiating LB, the tasks assigned to the overloaded VM are reallocated to under loaded VMs. Here, the proposed LB algorithm adapts capacity and loads for the reallocation. Based on TPF and VPF, the tasks are reallocated from VMs using the proposed EHGWO. The proposed EHGWO is developed by integrating EHO and GWO algorithm using a new fitness function formulated by load of VM, migration cost, load of VM, capacity of VM and makespan. The proposed EHGWO is analyzed based on load and makespan.

Multitube Helical-Waveguide Gyrotron Traveling-Wave Amplifier: Device Concept and Electron-Optical System Modeling

A multitube configuration for a gyrotron traveling-wave amplifier (gyro-TWA) that is based on the use of one multibeam electron gun and several parallel helically corrugated interaction waveguides operating with axis-encircling-like electron beamlets at the second cyclotron harmonic is proposed. This new gyro-TWA concept, similar to that for multibeam or clustered linear-beam klystrons, can provide a multifold decrease in the thermal loading and increase in the RF breakdown strength for each tube at the same average or pulse output powers or a significant increase in the output power at a moderate level of the mentioned factors. It is shown that the multibeam electron flow appropriate for such a multitube gyro-TWA can be formed by a single magnetron-injection gun (MIG) using selectively emitting regions on the cathode. In some cases, such a gun can be less sensitive to the influence of space-charge forces and other disturbing factors and generate a beam of better quality than a single-beam cusp gun. In particular, a gun for the ten-tube ${W}$ -band gyro-TWA, which ensures generation of a beam with a total power of about 1.3 MW, a pitch factor from 1.2 to 1.5, and a root-mean-square (rms) transverse velocity spread of about 8%, was designed and numerically modeled.

Universal Electron Gun Design for a CW Third Harmonic Gyrotron with an Operating Frequency over 1 THz

The design of a magnetron-injection gun (MIG) suitable for using in the CW 3-rd harmonic gyrotron with an output frequency of 1.185 THz and an output power about 100 W, intended for DNP/NMR spectroscopy applications is described. To improve the mode selection, several electron optics schemes are investigated. The MIG allows using both single-beam and double-beam schemes of the gyrotron operation with two different operating modes. Requirements for the electron beam parameters were found. The design of the triode MIG forming two generating beams with a quality suitable for 3-rd harmonic operation is suggested and optimized. The specific feature of the MIG is the possibility to form either two beams or one beam using the same electrode geometry and different number of emitting rings. The suggested MIG is not sensitive to small misalignment and reasonable manufacturing errors. A key feature of the design is that to improve the mode selection an electron beam with increased velocity spread is proposed. It is shown that it is possible to form two beams with practically equal and quite high pitch factors in all range of operating currents and at the same time small enough coefficient of reflection from the magnetic mirror in spite of large enough value of velocity spread.

Voice Conversion Using a Perceptual Criterion

In voice conversion (VC), it is highly desirable to obtain transformed speech signals that are perceptually close to a target speaker’s voice. To this end, a perceptually meaningful criterion where the human auditory system was taken into consideration in measuring the distances between the converted and the target voices was adopted in the proposed VC scheme. The conversion rules for the features associated with the spectral envelope and the pitch modification factor were jointly constructed so that perceptual distance measurement was minimized. This minimization problem was solved using a deep neural network (DNN) framework where input features and target features were derived from source speech signals and time-aligned version of target speech signals, respectively. The validation tests were carried out for the CMU ARCTIC database to evaluate the effectiveness of the proposed method, especially in terms of perceptual quality. The experimental results showed that the proposed method yielded perceptually preferred results compared with independent conversion using conventional mean-square error (MSE) criterion. The maximum improvement in perceptual evaluation of speech quality (PESQ) was 0.312, compared with the conventional VC method.

An analysis of the calibration method of accelerometer bias and scale factor

Accelerometer bias and scale factor are important parameters of the accelerometer. The accuracy of calibration of bias and scale factor will directly affect navigation accuracy. This paper studies the calibration of accelerometers under out-door conditions. In some applications, the inertial measurement unit (IMU) cannot rotate with any angle due to the restriction of equipment and site. The pitch and roll rotation range is -45° to 45°, and the yaw is -180° to 180°. In this paper, the bias and scale factor identification equations under different positions are derived based on the inertial navigation error equation. The results show that when the IMU rotates around the pitch axis, as long as there are three pitch positions, the bias and scale factor of the y-direction and z-direction accelerometers can be calibrated. When the IMU rotates 45° around the roll axis and then rotates 90° around the yaw axis, the x-direction accelerometer scale factor can be calibrated. If the bias and scale factor of the y-direction and z-direction accelerometer are known, the bias of the x-direction accelerometer can also be calibrated. Then, several simulations are conducted which are consistent with the theoretical results. At last, optimized calibration path is designed. Within 20 min, the calibration accuracy of bias is better than 5 mGal, and the calibration accuracy of scale factor is better than 5 ppm.

Optimization of acquisition parameters for reduced-dose thoracic CT: A phantom study

PurposeThe purpose of this study was to analyze the impact of different options for reduced-dose computed tomography (CT) on image noise and visibility of pulmonary structures in order to define the best choice of parameters when performing ultra-low dose acquisitions of the chest in clinical routine. Materials and methodsUsing an anthropomorphic chest phantom, CT images were acquired at four defined low dose levels (computed tomography dose index [CTDIvol]=0.15, 0.20, 0.30 and 0.40mGy), by changing tube voltage, pitch factor, or rotation time and adapting tube current to reach the predefined CTDIvol-values. Images were reconstructed using two different levels of iteration (adaptive statistical iterative reconstruction [ASIR®]-v70% and ASIR®-v100%). Signal-to-noise ratio (SNR) as well as contrast-to-noise ratio (CNR) was calculated. Visibility of pulmonary structures (bronchi/vessels) were assessed by two readers on a 5-point-Likert scale. ResultsBest visual image assessments and CNR/SNR were obtained with high tube voltage, while lowest scores were reached with lower pitch factor followed by high tube current. Protocols favoring lower pitch factor resulted in decreased visibility of bronchi/vessels, especially in the periphery. Decreasing radiation dose from 0.40 to 0.30mGy was not associated with a significant decrease in visual scores (P<0.05), however decreasing radiation dose from 0.30mGy to 0.15mGy was associated with a lower visibility of most of the evaluated structures (P<0.001). While image noise could be significantly reduced when ASIR®-v100% instead of ASIR®-v70% was used, the visibility-scores of pulmonary structures did not change significantly. ConclusionFavoring high tube voltage is the best option for reduced-dose protocols. A decrease of SNR and CNR does not necessarily go along with reduced visibility of pulmonary structures.

Low-Voltage Operation of the Double-Beam Gyrotron at 400 GHz

For the double-beam THz gyrotron, an efficient operation under nonrelativistic acceleration voltages is experimentally demonstrated. The output power at the frequency of 0.4 THz was 60 W for an operating voltage of 5.4 kV, and the starting voltage was as low as 2.4 kV; that is in good agreement with calculations. The starting voltage can be further decreased, and the output power can be increased by increasing the beam pitch factor at low voltages. Simulations of three-electrode magnetron injection gun (MIG) show that it can be achieved by the optimized MIG geometry and by applying the positive voltage at the modulating anode.

Evaluation of Optimal Combination of Planning Parameters (Field Width, Pitch, and Modulation Factor) in Helical Tomotherapy for Bilateral Breast Cancer.

Aim:The aim of the study was to find the most balanced plan with an optimal combination of planning parameters in helical tomotherapy (HT) for bilateral breast irradiation by evaluating dosimetric indices and time factors. In particular, we investigated the best combination of field width (FW), pitch, and modulation factor (MF).Materials and Methods:A total of 90 plans (18 plans for each patient) was created in this study, with different combination of planning parameters (FW: 2.5 cm [F1] and 5 cm [F2]; pitch: 0.215 [P1], 0.287 [P2], and 0.43 [P3]; and MF: 2.0 [M1], 2.5 [M2], and 3.0 [M3]). Plans were analyzed using several dosimetric indices: homogeneity index, conformity index, dose near minimum D98%, dose near maximum D2%, and the coverage by D95% of the target. Organ at risk (OAR) doses were evaluated by mean dose, V5Gy and V25Gy for the heart and mean dose V5Gy and V20Gy for both the lungs. Treatment time was also reported for all plans.Results:Reducing FW from 5 cm to 2.5 cm increased the treatment time by 40%–50% and improved homogeneity of the target. Tightening the pitch value from 0.43 to 0.215 improved target as well as OAR doses without increasing the treatment time. Increasing MF from 2 to 3 improved all the dosimetric indices and also increased treatment time.Conclusions:On the basis of our analysis, a plan with FW 5 cm, pitch 0.215, and MF 2.5 can be considered as an optimal combination of planning parameters for bilateral breast irradiation in HT technique.

Assessment of Diagnostic Reference Dose Associated with Computed Tomography Examination

The current study is aimed to estimate the diagnostic reference dose levels (DRLs), the volume computer tomogram dose index (CTDIvol), the CT air kerma-length product (PKL,CT) and the effective dose (E) for head, chest and chest-abdomen-pelvic CT examinations performed on adults in King Abdullah Medical City (KAMC), Saudi Arabia. Demographic parameters (such as age, gender, weight, height) for a sample of 535 computed tomography (CT) patients and physical scan parameters (such as patient tube voltage (kV), reference and effective mill ampere-second (mAs), scan length, number of slices, and pitch factor) were collected from a picture archiving and communication system (PACS). CTDIvol and PKL,CT were studied for different patients weights (40 -60 kg, 60-80 kg, 80-100 kg and 100-120 kg). Mean CTDIvol, PKL,CT and effective dose for a standard weight (70 kg ±10%) was evaluated according to the three CT protocols considered and the results were, as follows: for head examinations – 61.8 mGy, 1212 mGy.cm and 2.55 mSv, respectively; for chest examinations- 13.1 mGy, 657.5 mGy.cm and 9.21 mSv, respectively; for chest-abdomen-pelvic examinations - 13.9 mGy, 782.5 mGy.cm and 11.73 mSv, respectively. The effective dose for the chest examinations was lower than the corresponding value communicated by the European study group under European Commission. The effective dose for head examinations, was slightly higher than the one communicated by the European Commission study due to differences in the scan length. It needs optimizing the radiation dose delivered to patients via periodical review of scan parameters for a protocol under study.

Investigation on Ku-Band Dual-State Gyro-TWT

This article presents the development of a dual-state Ku -band gyrotron traveling-wave tube (gyro-TWT) dual-state curved-profile magnetic injection gun (MIG) generating high-quality electron beams, in which the pitch factor is up to 1.2 and 1.35 for the pulse wave (PW) state and the continuous wave (CW) state, separately. A multiobjective genetic algorithm (MOGA) is applied in the profile optimization. Meanwhile, the parametric sensitivity is also discussed in detail. A periodic dielectric-loaded interaction circuit is adopted to suppress oscillations. Furthermore, thermal analyses of the interaction circuit under different duty cycles are also elaborated. The interaction circuit is analyzed in accordance with the proposed nonlinear self-consistent theory and particle-in-cell (PIC) codes. The results of hot experiments show that the dual-state tube obtains the output power of 150/30 kW corresponding to a saturated gain of 40/41 dB and the maximum efficiency of 25%/21% within the bandwidth of 2.0/1.1 GHz for the PW/CW state, respectively.

Nonadiabatic Effects on Beam-Quality Parameters for Frequency-Tunable Gyrotrons

We propose an unconventional electron gun structure in which the emitter is located on a concave cathode surface with a non-uniform electric field. Such a design violates the intuition that an emitter should place close to a uniform electric field to reduce the velocity spread. The commonly employed design guide based on the adiabatic condition predicts a huge velocity spread of 24%, but the simulation using EGUN code and verified with CST particle studio shows a very low spread of 2.8%. Examining the magnetic moment and the kinetic energy of the beam reveals that the electrons experience a relatively long acceleration process due to the much weak electric field. That's why the non-adiabatic effect matters. In addition to the cyclotron compression and the E$\times$B drift, the "resonant" polarization drift plays a crucial role in reducing the overall velocity spread.Simulations show a decent beam quality with the pitch factor of 1.5 and the transverse velocity spread of 2.8% over a wide range of the magnetic field (7.4-8.0 T) and the beam voltage (12-22 kV) with a high structural tolerance. The promising results with the wide working range enable the development of continuous frequency-tunable gyrotrons.

OPTIMIZATION OF RADIATION DOSE IN CT IMAGING: ESTABLISHING THE INSTITUTIONAL DIAGNOSTIC REFERENCE LEVELS AND PATIENT DOSE AUDITING.

The aim of this study was to propose local diagnostic reference levels (LDRLs) for the most common computed tomography (CT) examinations (including contrast and non-contrast scan phase) performed at Advanced Medical and Dental Institute (AMDI), Universiti Sains Malaysia (USM), Malaysia. A retrospective CT dose survey of 1488 subjects from January 2015 until December 2018 was performed at AMDI USM, Malaysia. The proposed DRLs were established at 50th and 75th percentile of dose distribution for all dose metrics (CT dose index [CTDI]; CTDIvol, CTDIw and dose-length product). The proposed LDRLs were compared with national DRLs and other established DRLs. The 10 most common CT examinations at AMDI were thorax-abdomen-pelvis (TAP) CT (46%), followed by pelvis CT (17%), abdomen-pelvis CT (10%), brain/head CT (9%) and other CT protocols. The local DRLs were established using the third quartile values of dose distribution and were categorized based on CT region protocols. Most of the proposed DRLs were exceeded the national DRLs (63%) and other international DRLs (67%). From the dose auditing, almost half of the recent dose data (for year 2018) exceeded the proposed local DRLs and the unusual dose were observed in TAP, brain/head and pelvis CT examinations. The unusual higher dose could be due to higher mAs settings, higher number of scan phase for contrast study and higher pitch factor. The local DRLs should be established for dose optimization and reduction of the occurrence of excessive radiation exposure to the patients. The establishment of the Ads and LDRLs should also consider all the factors that affect the variation in DRLs such as CT technology, scanning protocols and population characteristics. The local dose distribution should always be revised for improvement of the current local practice.

Comparative Analysis of Flux Reversal Permanent Magnet Machines With Toroidal and Concentrated Windings

In this article, the flux reversal permanent magnet (FRPM) machine with toroidal windings is presented and analyzed with reference to conventional concentrated windings. First, the influence of rotor pole numbers on FRPM machines with conventional concentrated windings is investigated. It is found that although the 12/13 stator slot/rotor pole FRPM machine has a high back electromotive force, the pitch factor, and magnet flux utilization ratio of concentrated windings are very low. By adopting toroidal windings instead of concentrated windings in the 12/13 FRPM machine, the pitch factor and resulted machine performance can be effectively improved. Finite-element analysis shows that the 12/13 FRPM machine with toroidal windings can produce 79% higher torque than its counterpart with concentrated windings. Then, the critical design parameters and detailed electromagnetic performance of FRPM machines with both winding types are analyzed and compared. It is shown that the machine with toroidal windings has higher torque, efficiency, power factor, and lower torque ripple, making it particularly suitable for low-speed, high-torque, and axial length limited applications. In addition, other feasible stator slot/rotor pole combinations to use toroidal winding are identified, with the aid of equivalent pole-pair number. Finally, two 12/13 FRPM prototypes with toroidal windings and concentrated windings are tested to validate the analyses.

How to CT scan human mummies: Theoretical considerations and examples of use

ObjectiveThe purpose of this study was to develop and provide recommendations for computed tomography (CT) examinations of human mummies. Materials and methodsBased on theoretical considerations and examples, recommendations for use are provided for scanning and image reconstruction parameters. Four examples are presented to illustrate the effect of different CT parameters on image quality. ResultsThe use of appropriate scanning parameters (detector collimation, pitch factor, rotation time) is known to improve image quality; technical considerations favor using lower tube voltage and higher tube current values for the purposes of scanning of human mummies. The use of appropriate image reconstruction parameters (slice thickness, increment, field of view, reconstruction filters) are the basis for individual reconstructions for the purpose of evaluation, documentation, illustration and data storage. ConclusionsDownsizing the field of view to the region of interest as done in the clinical radiological routine represents one major tool to improve image quality. SignificanceThe provided recommendations should improve CT image quality in mummy studies as well as the handling of image data for reconstructions and storage. LimitationsThe recommendations for CT scanning parameters and image reconstructions were written with relatively new generation CT scanners in mind. Only a few examples of use were chosen and image quality assessment was performed subjectively and not by quantitative measurements.

Triode Type Coaxial Inverse Magnetron Injection Gun for 2-MW, 240-GHz Gyrotron

A triode type coaxial inverse magnetron injection gun (CIMIG) is designed using the 2-D and 3-D beam trajectory simulation codes for 240-GHz, 2-MW coaxial gyrotron. In IMIG, the modulating anode is adjusted at the center of the emitter ring and it provides compact size and better control on the beam instability and beam halo. As per the beam-wave interaction simulations, the CIMIG is designed to deliver the 6.5-MW (100 kV, 65 A) helical electron beam of 8.72-mm guiding center radius at the cavity center. First, the synthesis of CIMIG is performed to estimate a range of electrical and geometrical parameters based on the tradeoff equations. The Gaussian type of magnetic field profile is optimized with the peak magnetic field value of 10 T at cavity center and the beam compression ratio of 35.11. The pitch factor of 1.306 and the transverse velocity spread of 2.74% are realized in 2-D trajectory code electron GUN. The design results obtained in 2-D simulations are validated in 3-D particle trajectory simulator CST-Particle Studio. In 3-D optimization, the gun geometry and the electrical parameters are kept similar to 2-D design. The pitch factor of 1.285 and transverse velocity spread of 3.01% are obtained in 3-D design which shows good agreement with the 2-D design.

The impact of pitch and modulation factor to Tomotherapy treatment plan optimization for motion target

The influence on target motion resulted from the respiratory process, the pitch and modulation factor presented in Tomotherapy. This study was aimed to investigate the effect of motion management using CT-images obtained from the fusion process between the static and dynamic scanning mode on the CIRS Thorax Phantom. The images were created using axial and helical modes which amplitudes were varied from 10 mm, 15 mm, and 20 mm. Then, the organ structures were planned using TomoPlan TPS with the variation of pitch ranging from 0.25 to 0.5, and the modulation factor (MF) in the range 2 to 3. Furthermore, evaluation of radiotherapy planning was performed using dose parameters on target, the organ at risk, homogeneity index (HI), and mean leaf open time (LOT). Target volume for static mode was 3.53 cc, whereas target volume has changed to 10.9 cc, 10.3 cc, 16.1 cc for axial and 6.6 cc, 8.5 cc, 14.9 cc for helical scanning. The HI value obtained was less than 0.07 and lower HI was resulted for a larger MF. It means that the higher modulation factor values will provide a uniform dose distribution to the target and lower dose to the OAR. The greater value of pitch gave the greater mean LOT. The optimum parameters were at the pitch of 0.5 and MF of 3 based on the evaluation of mean LOT and HI. Axial scanning mode provides a larger target volume compared to a helical scanning mode. Therefore, the increment of the target volume in delineating organ should be considered.

Development of High-Efficiency Gyro-TWT With a Nonuniform Dielectric-Loaded Circuit

This paper presents the development of highly efficient gyrotron traveling-wave tube (gyro-TWT) with a nonuniform dielectric-loaded interaction circuit. The high-quality electron beam has been generated by curved-profile magnetron injection gun (MIG). With regard to the profile optimization, simulated annealing algorithm (SAA) and genetic algorithm (GA) are applied. An electron beam with a pitch factor of 1.6 and low-axial velocity spread of 0.9182% have been obtained. The parametric sensitivity is discussed in detail. A nonuniform dielectric-loaded circuit has been employed to suppress both global oscillations and local oscillations. Different thicknesses of dielectric materials have been manufactured and measured, demonstrating the circuit loss of oscillation modes that are enough for stable operation. The interaction circuit is analyzed under the guidance of nonlinear self-consistent theory and particle-in-cell (PIC) codes. The tube achieves a saturated peak output power of 36.24 kW at 93 GHz, corresponding to a saturated gain of 54 dB and a maximum efficiency of 45.3% within a 3-dB saturated bandwidth of 5 GHz.

Effect of pitch on CT image quality based on SNR evaluation using in house phantom

The purpose of this study was aimed to evaluate the symmetrical effect of pitch factor to SNR (Signal to Noise Ratio) in thorax phantom CT images. Thorax CT phantom was designed to contain cork and cylindrical objects with several sizes located symmetrically respect to Y-axis. Phantom size is 20 cm diameter, 22 cm length, and the objects simulated vessels filled with contrast medium (diameter A: 2mm, B: 1.7 mm, C: 1 mm, respectively). The distance between two objects: A: 6 cm, B: 8 cm, and C: 12 cm. Image acquisitions were performed:130 kVp, tube rotation 0.6s, 70 mAs, and pitch values were 0.5, 0.8, 1.0, 1.5, 1.8 and 2.0. CT images represented by 9 axial images with a slice thickness of 5 mm. The difference of SNRs (Δ): a value of ΔA, in general high at initial slice and fall significantly up to the third slice and then followed by a nearly constant value. ΔB at initial slice trend decreased with increasing slice images. ΔC at all pitch initially shown zero value and increase to maximum up to second slice (not more than 20 units) and tend to constant after at sixth slice. Effect of all pitch values on symmetrical object images was influenced by the distance between two corresponding objects and slice order. Generally at the initial slice, the SNR difference between two corresponding objects (Δ) relatively high compared with the following order slice. Therefore, in clinical practice, it is recommended to give additional FOV at least 1.5 cm at the initial slice interest.

Logical Effort Framework for CNFET-Based VLSI Circuits for Delay and Area Optimization

Carbon nanotube field-effect transistors (CNFETs) show great potential to build digital systems on advanced technology nodes with big benefits in terms of power, performance, and area (PPA). However, CNFET-specific additional features such as the number of tubes, pitch (spacing between tubes), tube position, and diameter in array of tubes play a significant role in accurate PPA evaluation. Furthermore, count and density variations in carbon nanotubes (CNTs) due to manufacturing limitations, like the presence of metallic tubes in the CNFET channel, degrade the anticipated PPA benefits. Moreover, modeling the CNFET parameters, CNT variations and etching techniques for CNTs create additional complexity during performance optimization. Hence, for realistic optimization of CNFET circuit’s performance, it is imperative to incorporate the impact of these parameters and variations. In this paper, we propose delay models [pitch-aware logical effort (PALE) and position-aware pitch factor (PAPF)] for fast and accurate performance evaluation by including the impact due to CNFET-specific parameters and CNT variations. These models are developed based on industry standard logical effort framework. Furthermore, we present an optimization tool using PALE and PAPF to minimize the delay and area of CNFET circuits. We deploy several circuit-level techniques prior to optimizing the tubes (CNTs) in the logic gates to achieve globally optimum solution. For better optimization of the circuits, we also include the impact of wire parasitic in estimating the delay of the individual gates. Our optimization tool results in the maximum and average delay improvement by 27% and 17%, respectively, and $2.5\times $ reduction in area for standard ISCAS and OpenSPARC benchmark circuits. Fast and fairly accurate delay computation in our optimization framework offers great runtime benefits as compared to state-of-the-art simulation and statistical-based methods.