Reduce Imaging Time Research Articles

Simultaneous multi-slice MR imaging of the hip at 3\u2009T to reduce acquisition times and maintain image quality

BackgroundNewly developed simultaneous multi-slice (SMS) scans are now being introduced as a clinical application in neuroimaging. We examined the feasibility of SMS scans for joint imaging. The purpose of the present study was to prospectively compare the resolution and specific absorption rate (SAR) obtained using SMS to those of conventional methods in hip joint magnetic resonance imaging (MRI) and establish whether imaging times may be reduced using SMS in 3 T MRI and if image quality is affected.MethodsTwenty-one patients (4 men and 17 women, average age, 51.5 years, range: 22 to 76 years) with hip pain underwent MR examinations of the unilateral hip joint. Three board-certified radiologists independently and blindly evaluated the images obtained with and without SMS using window and level settings and magnification according to personal preferences. Individual SAR values were measured for each protocol. A Wilcoxon signed-rank test and a t-statistic test were used for statistical analyses. Signal-to-noise ratio (SNR) was also compared using a phantom.ResultsSMS imaging maintained equivalent image quality to conventional imaging for evaluating the morphology of the hip joint, and also reduced imaging times by approximately 40%. SMS images had significantly higher SAR values than conventional images. The rate of difference (SMS/conventional) in SNR ranged between 80 and 111%.ConclusionsBased on its significantly lower acquisition times and the maintenance of similar image quality to conventional imaging, SMS may be applied to morphological evaluations of hip joint disorders without significantly increasing SAR.

Improved Parallel Magnertic Resonance Imaging reconstruction with Complex Proximal Support Vector Regression

Generalized Auto-calibrating Partially Parallel Acquisitions (GRAPPA) has been widely used to reduce imaging time in Magnetic Resonance Imaging. GRAPPA synthesizes missing data by using a linear interpolation of neighboring measured data over all coils, thus accuracy of the interpolation weights fitting to the auto-calibrating signal data is crucial for the GRAPPA reconstruction. Conventional GRAPPA algorithms fitting the interpolation weights with a least squares solution are sensitive to interpolation window size. MKGRAPPA that estimates the interpolation weights with support vector machine reduces the sensitivity of the k-space reconstruction to interpolation window size, whereas it is computationally expensive. In this study, a robust GRAPPA reconstruction method is proposed that applies an extended proximal support vector regression (PSVR) to fit the interpolation weights with wavelet kernel mapping. Experimental results on in vivo MRI data show that the proposed PSVR-GRAPPA method visually improves overall quality compared to conventional GRAPPA methods, while it has faster reconstruction speed compared to MKGRAPPA.

Large-area single photon compressive imaging based on multiple micro-mirrors combination imaging method

We demonstrate a single photon compressive imaging system with the image plane up to the entire digital micro-mirror device (DMD) work area. A parallel light source is designed to reduce the influence of light scattering on imaging resolution and a photon counting photomultiplier tube (PMT) with a large photosensitive area is used to effectively collect light reflected from the full screen of DMD. A control and counting circuit, based on Field-Programmable Gate Array (FPGA), is developed to load binary random matrix into the DMD controller for each measurement, and to count single-photon pulse output from PMT simultaneously. To reduce imaging time and huge memory occupation for image reconstruction, a multiple micro-mirrors combination imaging method is proposed. The signal-to-noise ratio and detection limit of the imaging system is theoretically deduced. Theoretical analysis and experimental results show that micro-mirrors combination imaging method is more suitable for faster imaging in a weaker-light-level environment. In order to achieve high imaging quality, the size of the combined pixels and the average time of each measurement should be moderate, so that the impact of Poisson shot noise is minimized.

Introduction to the Technical Aspects of Computed Diffusion-weighted Imaging for Radiologists.

Diffusion-weighted (DW) imaging is a magnetic resonance (MR) imaging method. It is an indispensable sequence for the diagnosis of acute cerebral infarction and is recognized as a standard tool in oncologic imaging. Computed DW imaging refers to the synthesizing of arbitrary b-value DW images from a set of measured b-value images by voxelwise fitting. Computed DW imaging is advantageous because it generates DW images with a higher diffusion effect than that achievable by using the MR imaging units in use today. Additionally, computed DW imaging can reduce imaging time while producing images characterized by a higher signal-to-noise ratio than what the acquired DW images would display at the corresponding b values. By fitting input images acquired at a lower b value and correspondingly a shorter echo time, the signal intensity of the resulting computed DW image is closer to the ideal case. Computed DW images are generated by employing mathematical models that use mono-, bi-, or triexponential equations. To generate accurate computed DW images, the appropriate model must be selected, and the image parameters for the input data must be chosen accordingly. In addition, to reduce artifacts on computed DW images, the misalignment of input data must be corrected with the aid of image registration techniques. ©RSNA, 2018.

Read-out segmented echo planar diffusion imaging of the female pelvis-utility in endometrial carcinoma-a preliminary experience.

Susceptibility artefacts from bones and bowel, geometric distortion makes diffusion imaging of the pelvis difficult. We discuss the difficulties of single-shot-echo-planar(ss-ep)DWI and evaluate a new diffusion-weighted imaging (DWI)technique-readout segmented echo planar(rs-ep)DWI in endometrial carcinoma and discuss the imaging physics. Institute review board approval was obtained and five consecutive patients underwent both rs-ep and ss-ep-DWI of the female pelvis and two radiologists compared the images. ROIs were drawn on the endometrium on the b400 images-signal to noise was calculated and compared using Ftest. The rs-ep-DWI had less imaging artefacts, less bowel-related susceptibility and geometric distortion compared to ss-ep-DWI. There was statistically significant greater SNR in ss-ep-DWI compared to rs-ep-DWI. This resulted in increased graininess of the readout segmented diffusion images. Artefacts in SS-EPI-DTI may make fibre tracking fallacious and rs-ep DTI may have fewer artefacts. rs-ep-DWI is a new imaging arsenal in imaging of the female pelvis in general; however further reduction in imaging time and improvement in signal to noise may be desirable. rs-ep-DWI affords lesser imaging artefacts from susceptibility and geometric distortion; at a higher time dividend and may find a place in oncological imaging.

Pelvic MRI staging of endometriosis at 3 T without patient preparation or anti-peristaltic: Diagnostic performance outcomes

PurposeEndometriosis is a disease of significant burden among pre-menopausal women characterised by the appearance of functional endometrial tissue in locations outside the uterus. Deep infiltrating endometriosis (DIE) is an invasion of the endometriotic lesion that exceeds 5 mm in depth into the peritoneum. In most cases, pelvic MRI is the imaging modality of choice for the pre-operative workup for DIE to guide surgery. The recommended standard for pelvic MRI images is at 1.5 T with patient preparations in the form of laxatives, anti-spasmodics and/or rectal contrast. However, there appears to be equally diagnostic quality imaging obtainable with a 3 T system using fast imaging acquisition without any patient preparation. This reduces imaging time, movement artefacts, is more comfortable for the patient and is easier for workflow coordination. This study aims to confirm that this approach reaches diagnostic performance outcomes comparable to reported international standards, particularly in the detection of endometriotic bowel lesions, in order to guide surgical pre-operative planning. Methods and MaterialsPre-operative diagnostic radiology reports were identified by a search of the Radiology Information System (RIS) for all pelvic MRI studies performed at a tertiary referral centre, King Edward Memorial Hospital for Women, between January 2015 to April 2017 that contained the keyword “endometriosis”. Reported sites of endometriotic deposits at MRI findings were tallied based on anatomical location and correlated to laparoscopic surgical report findings and/or pathology report as a reference standard. Pooled sensitivities and specificities were then calculated and compared with established studies. ResultsNinety-eight MRI studies were identified, of which 76 identified DIE and 22 were normal studies. Sixty-one patients did not have a surgical or pathology record. Of the remainder who underwent laparoscopy, operative and/or pathology reports were obtainable in 37 female patients, with a median age of 35 years (range: 24 to 49 years). The average time interval from MRI report to surgical operation was 195 days (range: 5 to 563 days). Middle compartment estimated sensitivity was 79.4% (95% CI = (69.4%, 89.4%)), specificity 95.1% (95% CI = (91.2%, 98.9%)). Posterior compartment estimated sensitivity was 76.5% (95% CI = (66.4%, 86.6%)), specificity 99.4% (95% CI = (98.1%, 100%)). Overall sensitivity 76.9% (95% CI = (69.7%, 84.0%)), specificity 98.5% (95% CI = (97.3%, 99.6%)). Sensitivity and specificity of detecting bowel endometriosis were estimated to be 94.4% (95% CI = (83.9%, 100%) and 94.7% (84.7%, 100%)) respectively. ConclusionUsing a 3 T MRI system without patient preparation is feasible and achieves benchmark diagnostic performance outcomes in the pre-operative assessment for DIE, especially in detecting posterior compartment lesions and bowel DIE to correctly guide surgical planning.

Feature Tracking for High Speed AFM Imaging of Biopolymers.

The scanning speed of atomic force microscopes continues to advance with some current commercial microscopes achieving on the order of one frame per second and at least one reaching 10 frames per second. Despite the success of these instruments, even higher frame rates are needed with scan ranges larger than are currently achievable. Moreover, there is a significant installed base of slower instruments that would benefit from algorithmic approaches to increasing their frame rate without requiring significant hardware modifications. In this paper, we present an experimental demonstration of high speed scanning on an existing, non-high speed instrument, through the use of a feedback-based, feature-tracking algorithm that reduces imaging time by focusing on features of interest to reduce the total imaging area. Experiments on both circular and square gratings, as well as silicon steps and DNA strands show a reduction in imaging time by a factor of 3–12 over raster scanning, depending on the parameters chosen.

Optimization of selective inversion recovery magnetization transfer imaging for macromolecular content mapping in the human brain.

To optimize a selective inversion recovery (SIR) sequence for macromolecular content mapping in the human brain at 3.0T. SIR is a quantitative method for measuring magnetization transfer (qMT) that uses a low-power, on-resonance inversion pulse. This results in a biexponential recovery of free water signal that can be sampled at various inversion/predelay times (tI/ tD ) to estimate a subset of qMT parameters, including the macromolecular-to-free pool-size-ratio (PSR), the R1 of free water (R1f ), and the rate of MT exchange (kmf ). The adoption of SIR has been limited by long acquisition times (≈4 min/slice). Here, we use Cramér-Rao lower bound theory and data reduction strategies to select optimal tI /tD combinations to reduce imaging times. The schemes were experimentally validated in phantoms, and tested in healthy volunteers (N = 4) and a multiple sclerosis patient. Two optimal sampling schemes were determined: (i) a 5-point scheme (kmf estimated) and (ii) a 4-point scheme (kmf assumed). In phantoms, the 5/4-point schemes yielded parameter estimates with similar SNRs as our previous 16-point scheme, but with 4.1/6.1-fold shorter scan times. Pair-wise comparisons between schemes did not detect significant differences for any scheme/parameter. In humans, parameter values were consistent with published values, and similar levels of precision were obtained from all schemes. Furthermore, fixing kmf reduced the sensitivity of PSR to partial-volume averaging, yielding more consistent estimates throughout the brain. qMT parameters can be robustly estimated in ≤1 min/slice (without independent measures of ΔB0 , B1+, and T1 ) when optimized tI -tD combinations are selected.

Toward faster inference of micron-scale axon diameters using Monte Carlo simulations

Recent advances have allowed oscillating gradient (OG) diffusion MRI to infer the sizes of micron-scale axon diameters. Here the effects on the precision of the inferred diameters are studied when reducing the number of images collected to reduce imaging time for clinical feasibility. Monte Carlo simulations of cosine OG sequences (50-1000Hz) using a two-compartment model on a parallel cylinder (diameters 1-5μm) geometry were conducted. Temporal diffusion spectroscopy was used to infer axon diameters. Three different gradient sets were simulated with different combinations of gradient strengths. Five frequencies were adequate for d=3-5μm with single-sized cylinders and for effective mean axon diameters greater than 2μm for cylinders with a distributions of diameters. There was some improvement in precision for d=1-2μm with 10 frequencies. It is better to repeat measurements at higher gradient strengths than to use a range of gradient strengths. The improvement tended to be greatest when using fewer frequencies and was especially noticeable at very high gradient strengths. Images can be collected with fewer gradient strengths and frequencies without sacrificing the precision of the measurements. This could be useful in reducing imaging time so that OG techniques can be used in clinical settings.

An Exploratory Study of Washout Rate Analysis for Thallium-201 Single-Photon Emission Computed Tomography Myocardial Perfusion Imaging Using Cadmium Zinc Telluride Detectors

The aim of this study was to assess the washout rate (WOR) for thallium-201-chloride single-photon emission computed tomography (SPECT) myocardial perfusion imaging (MPI) using cadmium zinc telluride detectors for SPECT (CZT SPECT) versus conventional Anger-type SPECT (conventional SPECT). A total of 52 Japanese patients were examined using CZT SPECT and conventional SPECT, and the global WORs were compared. Additionally, the MPI WORs were compared for patients with a normal MPI versus those in whom MPI reflected the patients’ multivessel disease (MVD) MPI. Washout rates were similar when approximated by CZT SPECT versus conventional SPECT 12.59 ± 2.26%/h vs 12.57 ± 2.27%/h (P = .997), respectively. The WOR values for CZT SPECT versus conventional SPECT were 13.42%/h (1.53%/h) vs 13.93%/h (1.24%/h) (P = .337), respectively, for 7 normal MPI patients, and 10.64 ± 2.20%/h vs 10.84 ± 2.26%/h (P = .848), respectively, for 7 MVD-MPI patients. The WOR values for normal MPI versus MVD-MPI patients for CZT SPECT were 13.42 ± 1.53%/h vs 10.64 ± 2.20%/h (P = .025), respectively. Thallium-201-chloride WOR values obtained with high-efficiency CZT SPECT, which enabled significantly reduced imaging times and use of a low-dose protocol, were similar to those obtained with conventional SPECT.

Optimal Spatial Sampling Criterion in a 2D THz Holographic Imaging System

This paper presents our study on the spatial sampling scheme in a 2-D terahertz holographic imaging system operating at 220 GHz, in which the amplitude and phase of reflected/scattered signal from the target are recorded by raster scanning on the aperture plane. The amplitude and phase based image reconstruction has been proved better than the amplitude based image. Traditionally, the spatial sampling interval, which needs to satisfy the Nyquist sampling criterion, has mostly been selected based on the worst case scenario. However, smaller spatial sampling interval will introduce more time consumption in the scanning. We have derived in theory an optimal spatial sampling criterion based on the target size and the threshold power beam width of transmitter/receiver antenna. The optimal spatial sampling interval is much larger than the worst case Nyquist criterion and has been verified in the experiment, leading to a substantially reduced imaging time while maintaining the image quality.

Real-time scan speed control of the atomic force microscopy for reducing imaging time based on sample topography

Here, a novel method, real-time scan speed control for raster scan amplitude modulation atomic force microscopes (AM-AFMs), is proposed. In general, the imaging rate is set to a fixed value before the experiment, which is determined by the feedback control calculations on each imaging point. Many efforts have been made to increase the AFM imaging rate, including using the cantilever with high eigenfrequency, employing new scan methods, and optimizing other mechanical components. The proposed real-time control method adjusts the scan speed linearly according to the error of every imaging point, which is mainly determined by the sample topography. Through setting residence time on each imaging point reasonably, the performance of AM-AFMs can be fully exploited while the scanner vibration is avoided when scan speed changes. Experiments and simulations are performed to demonstrate this control algorithm. This method would increase the imaging rate for samples with strongly fluctuant topography up to about 3 times without sacrificing any image quality, especially in large-scale and high-resolution imaging, in the meanwhile, it reduces the professional requirements for AM-AFM operators. Since the control strategy employs a linear algorithm to calculate the scanning speed based on the error signal, the proposed method avoids the frequent switching of the scanning speed between the high speed and the low speed. And it is easier to implement because there is no need to modify the original hardware of the AFM for its application.

Bone Marrow Metastases: T2-weighted Dixon Spin-Echo Fat Images Can Replace T1-weighted Spin-Echo Images.

Purpose To test the potential of Dixon T2-weighted fat-only sequences to replace T1-weighted sequences for the detection of bone metastases, with the hypothesis that diagnostic performance with an alternative magnetic resonance (MR) imaging protocol (sagittal spin-echo Dixon T2-weighted fat-only and water-only imaging) would not be inferior to that with the standard protocol (sagittal spin-echo T1-weighted and spin-echo Dixon T2-weighted water-only imaging). Materials and Methods A total of 121 consecutive whole-spine MR imaging examinations (63 men; mean age ± standard deviation, 61.4 years ± 11.8) performed for suspected vertebral bone metastases were included in this retrospective, institutional review board-approved study. Quantitative image analysis was performed for 30 randomly selected spine levels. Qualitative analysis was performed separately by two musculoskeletal radiologists, who registered the number of metastases for each spine level. Areas under the curve with the protocols were compared on the basis of nonparametric receiver operating characteristic curve estimations by using a noninferiority test on paired data, with a best valuable comparator as a reference. Interobserver and interprotocol agreement was assessed by using κ statistics. Results Contrast-to-noise ratio was significantly higher on the alternative protocol images than on the standard protocol images (181.1 [95% confidence interval: 140.4, 221.7] vs 84.7 [95% confidence interval: 66.3, 103.1] respectively; P < .001). Diagnostic performance was not significantly inferior with the alternative protocol than with the standard protocol for both readers in a per-patient analysis (sensitivity, 97.9%-98.9% vs 93.6%-97.9%; specificity, 85.2%-92.6% vs 92.6%-96.3%; area under the curve, 0.92-0.96 vs 0.95, respectively; all P ≤ .02) and a per-spine level analysis (all P < .01). Interobserver and interprotocol agreement was good to very good (κ = 0.70-0.81). Conclusion Dixon T2-weighted fat-only and water-only imaging provide, in one sequence, diagnostic performance similar to that of the standard combination of morphologic sequences for the detection of probable spinal bone metastases, thereby providing an opportunity to reduce imaging time by eliminating the need to perform T1 sequences. © RSNA, 2017 An earlier incorrect version of this article appeared online. This article was corrected on November 6, 2017.

Fast, Low-Dose Megavoltage-Topogram Localization in a Helical IGRT Unit: Initial Clinical Experience with Mesothelioma Patients

To present our initial clinical experience with malignant pleural mesothelioma (MPM) patients in Megavoltage (MV)-Topogram trial, for evaluating the potential of MV-Topogram-based alignment as an alternative to Megavoltage Computed Tomography (MVCT) in reducing imaging time and dose. Four mesothelioma patients were enrolled in an on-going Institutional Review Board (IRB)-approved MV-Topograms clinical trial at our institute. Patients were set up using the clinical protocol employing red lasers. Anterior-Posterior (AP) and lateral (LAT) MV-Topograms were acquired using gantry angles of 0°/90° with 1 mm collimator opening, all MLC leafs open, 4 cm/s couch speed, and 12.5 s scanning time. Routine MVCT scans were performed immediately afterwards. MV-Topograms were reconstructed and enhanced using contrast-limited adaptive histogram equalization (CLAHE). AP and LAT kilo voltage (kV) digital reconstructed topograms (DRT) images were reconstructed based on TomoTherapy geometry from CT simulation scans. Registrations between MV-Topograms and kV-DRT images were performed by a physicist manually. Due to image contrast limitations, the registration primarily involved aligning the carina. To be consistent with MV-Topograms, the same physicist re-aligned MVCTs to planning CT based on carina as well. Results were compared between MV-Topograms based shifts and the corresponding MVCT shifts. MV-Topogram and MVCT doses were measured using an ion-chamber in a 28 cm diameter cylindrical water-equivalent phantom at depths between 1-14 cm. The mean and standard deviation of shift discrepancies between MV-Topogram and MVCT were -0.52±1.35 mm, 2.51±2.40 mm, -0.24±4.09 mm in lateral, longitudinal and vertical directions for manual registrations. The dose ratio between MVCT and MV-Topogram ranged from 14.7 to 26.9 for depths between 1 cm and 14 cm, respectively. On average, the time required to acquire 38 cm long MVCT scans were five times more than a pair of 50 cm long MV-Topograms. Lateral and vertical shifts from MV-Topograms showed equivalent alignment results with MVCT. The greatest discrepancy between the MV Topograms and MVCT was in the longitudinal direction. This could be due to the breathing motion of the carina, which has been shown to be approximately 5 mm in the longitudinal direction. Substantial reductions of dose and acquisition time were observed for MV-Topogram. Challenges of employing bony anatomy for Topogram alignment were the relatively poor contrast and image artifacts caused by small dose rate fluctuations. Improving the linear accelerator dose stability would improve the ability to employ MV Topograms for patient alignment.

2D Normalized Iterative Hard Thresholding Algorithm for Fast Compressive Radar Imaging

Compressive radar imaging has attracted considerable attention because it substantially reduces imaging time through directly compressive sampling. However, a problem that must be addressed for compressive radar imaging systems is the high computational complexity of reconstruction of sparse signals. In this paper, a novel algorithm, called two-dimensional (2D) normalized iterative hard thresholding (NIHT) or 2D-NIHT algorithm, is proposed to directly reconstruct radar images in the matrix domain. The reconstruction performance of 2D-NIHT algorithm was validated by an experiment on recovering a synthetic 2D sparse signal, and the superiority of the 2D-NIHT algorithm to the NIHT algorithm was demonstrated by a comprehensive comparison of its reconstruction performance. Moreover, to be used in compressive radar imaging systems, a 2D sampling model was also proposed to compress the range and azimuth data simultaneously. The practical application of the 2D-NIHT algorithm in radar systems was validated by recovering two radar scenes with noise at different signal-to-noise ratios, and the results showed that the 2D-NIHT algorithm could reconstruct radar scenes with a high probability of exact recovery in the matrix domain. In addition, the reconstruction performance of the 2D-NIHT algorithm was compared with four existing efficient reconstruction algorithms using the two radar scenes, and the results illustrated that, compared to the other algorithms, the 2D-NIHT algorithm could dramatically reduce the computational complexity in signal reconstruction and successfully reconstruct 2D sparse images with a high probability of exact recovery.

Evaluation of general-purpose collimators against high-resolution collimators with resolution recovery with a view to reducing radiation dose in myocardial perfusion SPECT: A preliminary phantom study

BackgroundThere is a growing focus on reducing radiation dose to patients undergoing myocardial perfusion imaging. This preliminary phantom study aims to evaluate the use of general-purpose collimators with resolution recovery (RR) to allow a reduction in patient radiation dose. MethodsImages of a cardiac torso phantom with inferior and anterior wall defects were acquired on a GE Infinia and Siemens Symbia T6 using both high-resolution and general-purpose collimators. Imaging time, a surrogate for administered activity, was reduced between 35% and 40% with general-purpose collimators to match the counts acquired with high-resolution collimators. Images were reconstructed with RR with and without attenuation correction. Two pixel sizes were also investigated. Defect contrast was measured. ResultsDefect contrast on general-purpose images was superior or comparable to the high-resolution collimators on both systems despite the reduced imaging time. Infinia general-purpose images required a smaller pixel size to be used to maintain defect contrast, while Symbia T6 general-purpose images did not require a change in pixel size to that used for standard myocardial perfusion SPECT. ConclusionThis study suggests that general-purpose collimators with RR offer a potential for substantial dose reductions while providing similar or better image quality to images acquired using high-resolution collimators.

Performance of cardiac cadmium-zinc-telluride gamma camera imaging in coronary artery disease: a review from the cardiovascular committee of the European Association of Nuclear Medicine (EANM)

The trade-off between resolution and count sensitivity dominates the performance of standard gamma cameras and dictates the need for relatively high doses of radioactivity of the used radiopharmaceuticals in order to limit image acquisition duration. The introduction of cadmium-zinc-telluride (CZT)-based cameras may overcome some of the limitations against conventional gamma cameras. CZT cameras used for the evaluation of myocardial perfusion have been shown to have a higher count sensitivity compared to conventional single photon emission computed tomography (SPECT) techniques. CZT image quality is further improved by the development of a dedicated three-dimensional iterative reconstruction algorithm, based on maximum likelihood expectation maximization (MLEM), which corrects for the loss in spatial resolution due to line response function of the collimator. All these innovations significantly reduce imaging time and result in a lower patient's radiation exposure compared with standard SPECT. To guide current and possible future users of the CZT technique for myocardial perfusion imaging, the Cardiovascular Committee of the European Association of Nuclear Medicine, starting from the experience of its members, has decided to examine the current literature regarding procedures and clinical data on CZT cameras. The committee hereby aims 1) to identify the main acquisitions protocols; 2) to evaluate the diagnostic and prognostic value of CZT derived myocardial perfusion, and finally 3) to determine the impact of CZT on radiation exposure.

WE‐DE‐BRA‐09: Fast Megavoltage CT Imaging with Rapid Scan Time and Low Imaging Dose in Helical Tomotherapy

Purpose:Megavoltage computed tomography (MVCT) imaging has been widely used for daily patient setup with helical tomotherapy (HT). One drawback of MVCT is its very long imaging time, owing to slow couch speed. The purpose of this study was to develop an MVCT imaging method allowing faster couch speeds, and to assess its accuracy for image guidance for HT.Methods:Three cadavers (mimicking closest physiological and physical system of patients) were scanned four times with couch speeds of 1, 2, 3, and 4 mm/s. The resulting MVCT images were reconstructed using an iterative reconstruction (IR) algorithm. The MVCT images were registered with kilovoltage CT images, and the registration errors were compared with the errors with conventional filtered back projection (FBP) algorithm. Moreover, the fast MVCT imaging was tested in three cases of total marrow irradiation as a clinical trial.Results:Three‐dimensional registration errors of the MVCT images reconstructed with the IR algorithm were significantly smaller (p &lt; 0.05) than the errors of images reconstructed with the FBP algorithm at fast couch speeds (3, 4 mm/s). The scan time and imaging dose at a speed of 4 mm/s were reduced to 30% of those from a conventional coarse mode scan. For the patient imaging, a limited number of conventional MVCT (1.2 mm/s) and fast MVCT (3 mm/s) reveals acceptable reduced imaging time and dose able to use for anatomical registration.Conclusion:Fast MVCT with IR algorithm maybe clinically feasible alternative for rapid 3D patient localization. This technique may also be useful for calculating daily dose distributions or organ motion analyses in HT treatment over a wide area.

0005 : Prognostic value of myocardial perfusion SPECT without significant perfusion defect using a dual isotope protocol and a novel CZT camera: interim results of the PROMHETE study

New dedicated cardiac gamma cameras using CZT detectors have shown significant improvement over the Anger camera regarding physical parameters, and their diagnostic performances have been validated in clinical studies. To date, few studies have evaluated the prognostic value of a low to intermediate risk single-photon emission tomography (SPECT) myocardial perfusion imaging (MPI) with these cameras, and only one with a HSDI stress thallium-201/rest Technetium-99m protocol on a CZT camera. The study included patients who had no or minimal perfusion defects (<10% of the LV myocardium) on a HS-DI MPI following a symptom-limited treadmill test or a pharmacological stress testing. These 578 patients were followed for 3.3±0.4 years (95% complete). The main endpoint was the occurrence a hard cardiac event (cardiac death or nonfatal myocardial infarction). 212 patients (37%) underwent exercise stress and 366 (63%) had pharmacological stress (of which 89% had dipyridamole and 11% had dobutamine). Mean summed stress score was 0.95±1.2 [0-5]. During the follow-up period 25 hard cardiac events occurred. Annualized event rate was 1.3%/y. In the subgroup of patients undergoing exercise stress test, annualized event rate was 0.43%/y. Multivariate Cox analysis identified age (HR 1.14 [1.08; 1.20], p<0.0001) and rest LVEF (HR 0.95 [0.92; 0.98], p=0.008) as independent predictors of cardiac death or myocardial infarction. Survival analysis showed that the occurrence of cardiac events was significantly higher in patients who had an altered LVEF compared to patients with a normal LVEF (16% vs. 3.8%, p=0.003). The use of a HS-DI protocol on a CZT camera provides prognostic information, comparable to single-isotope protocols on conventional Anger camera, while reducing imaging time and without increasing the injected activity. The author hereby declares no conflict of interest

Investigation of cone-beam CT image quality trade-off for image-guided radiation therapy

It is well-known that projections acquired over an angular range slightly over 180° (so-called short scan) are sufficient for fan-beam reconstruction. However, due to practical imaging conditions (projection data and reconstruction image discretization, physical factors, and data noise), the short-scan reconstructions may have different appearances and properties from the full-scan (scans over 360°) reconstructions. Nevertheless, short-scan configurations have been used in applications such as cone-beam CT (CBCT) for head-neck-cancer image-guided radiation therapy (IGRT) that only requires a small field of view due to the potential reduced imaging time and dose. In this work, we studied the image quality trade-off for full, short, and full/short scan configurations with both conventional filtered-backprojection (FBP) reconstruction and iterative reconstruction algorithms based on total-variation (TV) minimization for head-neck-cancer IGRT. Anthropomorphic and Catphan phantoms were scanned at different exposure levels with a clinical scanner used in IGRT. Both visualization- and numerical-metric-based evaluation studies were performed. The results indicate that the optimal exposure level and number of views are in the middle range for both FBP and TV-based iterative algorithms and the optimization is object-dependent and task-dependent. The optimal view numbers decrease with the total exposure levels for both FBP and TV-based algorithms. The results also indicate there are slight differences between FBP and TV-based iterative algorithms for the image quality trade-off: FBP seems to be more in favor of larger number of views while the TV-based algorithm is more robust to different data conditions (number of views and exposure levels) than the FBP algorithm. The studies can provide a general guideline for image-quality optimization for CBCT used in IGRT and other applications.