Your browser doesn't support javascript.
loading
Show: 20 | 50 | 100
Results 1 - 20 de 36
Filter
1.
J Thorac Imaging ; 2024 Jul 22.
Article in English | MEDLINE | ID: mdl-39034758

ABSTRACT

PURPOSE: We sought to clinically validate a fully automated deep learning (DL) algorithm for coronary artery disease (CAD) detection and classification in a heterogeneous multivendor cardiac computed tomography angiography data set. MATERIALS AND METHODS: In this single-centre retrospective study, we included patients who underwent cardiac computed tomography angiography scans between 2010 and 2020 with scanners from 4 vendors (Siemens Healthineers, Philips, General Electrics, and Canon). Coronary Artery Disease-Reporting and Data System (CAD-RADS) classification was performed by a DL algorithm and by an expert reader (reader 1, R1), the gold standard. Variability analysis was performed with a second reader (reader 2, R2) and the radiologic reports on a subset of cases. Statistical analysis was performed stratifying patients according to the presence of CAD (CAD-RADS >0) and obstructive CAD (CAD-RADS ≥3). RESULTS: Two hundred ninety-six patients (average age: 53.66 ± 13.65, 169 males) were enrolled. For the detection of CAD only, the DL algorithm showed sensitivity, specificity, accuracy, and area under the curve of 95.3%, 79.7%, 87.5%, and 87.5%, respectively. For the detection of obstructive CAD, the DL algorithm showed sensitivity, specificity, accuracy, and area under the curve of 89.4%, 92.8%, 92.2%, and 91.1%, respectively. The variability analysis for the detection of obstructive CAD showed an accuracy of 92.5% comparing the DL algorithm with R1, and 96.2% comparing R1 with R2 and radiology reports. The time of analysis was lower using the DL algorithm compared with R1 (P < 0.001). CONCLUSIONS: The DL algorithm demonstrated robust performance and excellent agreement with the expert readers' analysis for the evaluation of CAD, which also corresponded with significantly reduced image analysis time.

3.
Radiol Artif Intell ; 4(2): e210196, 2022 Mar.
Article in English | MEDLINE | ID: mdl-35391773

ABSTRACT

The purpose of this work was to assess the performance of a convolutional neural network (CNN) for automatic thoracic aortic measurements in a heterogeneous population. From June 2018 to May 2019, this study retrospectively analyzed 250 chest CT scans with or without contrast enhancement and electrocardiographic gating from a heterogeneous population with or without aortic pathologic findings. Aortic diameters at nine locations and maximum aortic diameter were measured manually and with an algorithm (Artificial Intelligence Rad Companion Chest CT prototype, Siemens Healthineers) by using a CNN. A total of 233 examinations performed with 15 scanners from three vendors in 233 patients (median age, 65 years [IQR, 54-72 years]; 144 men) were analyzed: 68 (29%) without pathologic findings, 72 (31%) with aneurysm, 51 (22%) with dissection, and 42 (18%) with repair. No evidence of a difference was observed in maximum aortic diameter between manual and automatic measurements (P = .48). Overall measurements displayed a bias of -1.5 mm and a coefficient of repeatability of 8.0 mm at Bland-Altman analyses. Contrast enhancement, location, pathologic finding, and positioning inaccuracy negatively influenced reproducibility (P < .003). Sites with dissection or repair showed lower agreement than did sites without. The CNN performed well in measuring thoracic aortic diameters in a heterogeneous multivendor CT dataset. Keywords: CT, Vascular, Aorta © RSNA, 2022.

4.
Med Phys ; 48(7): 3479-3499, 2021 Jul.
Article in English | MEDLINE | ID: mdl-33838055

ABSTRACT

PURPOSE: In this work, we explore the potential of region-of-interest (ROI) imaging in x-ray computed tomography (CT). Using two dynamic beam attenuator (DBA) concepts for fluence field modulation (FFM) previously developed, we investigate and evaluate the potential dose savings in comparison with current FFM technology. METHODS: ROI imaging is a special application of FFM where the bulk of x-ray radiation is propagated toward a certain anatomical target (ROI), specified by the imaging task, while the surrounding tissue is spared from radiation. We introduce a criterion suitable to quantitatively describe the balance between image quality inside an ROI and total radiation dose with respect to a given ROI imaging task. It accounts for the mean image variance at the ROI and the effective patient dose calculated from Monte Carlo simulations. The criterion is further used to compile task-specific DBA trajectories determining the primary x-ray fluence, and eventually used for comparing different FFM techniques, namely the sheet-based dynamic beam attenuator (sbDBA), the z-aligned sbDBA (z-sbDBA), and an adjustable static operation mode of the z-sbDBA. Furthermore, two static bowtie filters and the influence of tube current modulation (TCM) are included in the comparison. RESULTS: Our findings demonstrate by simulations that the presented trajectory optimization method determines reasonable DBA trajectories. The influence of TCM is strongly depending on the imaging task. The narrow bowtie filter allows for dose reductions of about 10% compared to the regular bowtie filter in the considered ROI imaging tasks. The DBAs are shown to realize substantially larger dose reductions. In our cardiac imaging scenario, the DBAs can reduce the effective dose by about 30% (z-sbDBA) or 60% (sbDBA). We can further verify that the noise characteristics are not adversely affected by the DBAs. CONCLUSION: Our research demonstrates that ROI imaging using the presented DBA concepts is a promising technique toward a more patient- and task-specific CT imaging requiring lower radiation dose. Both the sbDBA and the z-sbDBA are potential technical solutions for realizing ROI imaging in x-ray CT.


Subject(s)
Technology , Tomography, X-Ray Computed , Humans , Monte Carlo Method , Phantoms, Imaging , Radiation Dosage , X-Rays
5.
Med Phys ; 47(10): 4827-4837, 2020 Oct.
Article in English | MEDLINE | ID: mdl-32754971

ABSTRACT

PURPOSE: We present a new concept for dynamic fluence field modulation (FFM) in x-ray computed tomography (CT). The so-called z-aligned sheet-based dynamic beam attenuator (z-sbDBA) is developed to dynamically compensate variations in patient attenuation across the fan beam and the projection angle. The goal is to enhance image quality and to reduce patient radiation dose. METHODS: The z-sbDBA consists of an array of attenuation sheets aligned along the z direction. In neutral position, the array is focused toward the focal spot. Tilting the z-sbDBA defocuses the sheets, thus reducing the transmission for larger fan beam angles. The structure of the z-sbDBA significantly differs from the previous sheet-based dynamic beam attenuator (sbDBA) in two features: (a) The sheets of the z-sbDBA are aligned parallel to the detector rows, and (b) the height of the sheets increases from the center toward larger fan beam angles. We built a motor actuated prototype of the z-sbDBA integrated into a clinical CT scanner. In experiments, we investigated its feasibility for FFM. We compared the z-sbDBA to common CT bowtie filters in terms of the spectral dependency of the transmission and possible image variance distribution in reconstructed phantom images. Additionally, the potential radiation dose saving using z-sbDBA for region-of-interest (ROI) imaging was studied. RESULTS: Our experimental results confirm that the z-sbDBA can realize variable transmission profiles of the radiation fluence by only small tilts. Compared to the sbDBA, the z-sbDBA can mitigate some practical and mechanical issues. In comparison to bowtie filters, the spectral dependency is considerably reduced when using the z-sbDBA. Likewise, more homogeneous image variance distributions can be attained in reconstructed phantom images. The z-sbDBA allows controlling the spatial image variance distribution which makes it suitable for ROI imaging. Our comparison on ROI imaging reveals skin dose reductions of up to 35% at equal ROI image quality by using the z-sbDBA. CONCLUSION: Our new concept for FFM in x-ray CT, the z-sbDBA, was experimentally validated on a clinical CT scanner. It facilitates dynamic FFM by realizing variable transmission profiles across the fan beam angle on a projection-wise basis. This key feature allows for substantial improvements in image quality, a reduction in patient radiation dose, and additionally provides a technical solution for ROI imaging.


Subject(s)
Tomography, X-Ray Computed , Humans , Phantoms, Imaging , Radiation Dosage , X-Rays
6.
Med Phys ; 46(12): 5528-5537, 2019 Dec.
Article in English | MEDLINE | ID: mdl-31348527

ABSTRACT

PURPOSE: It has been a long-standing wish in computed tomography (CT) to compensate the emitted x-ray beam intensity for the patient's changing attenuation during the rotation of a CT data acquisition. The patient attenuation changes both spatially, along the fan beam angle, and temporally, between different projections. By modifying the pre-patient x-ray intensity profile according to the attenuation properties of the given object, image noise can be homogenized and dose can be delivered where it is really needed. Current state-of-the-art bowtie filters are not capable of changing attenuation profiles during the CT data acquisition. In our work, we present the sheet-based dynamic beam attenuator (sbDBA), a novel technical concept enabling dynamic shaping of the transmission profile. METHODS: The sbDBA consists of an array of closely spaced, highly attenuating metal sheets, focused toward the focal spot. Intensity modulation can be achieved by controlled defocusing of the array such that the attenuation of the x-ray fan beam depends on the fan angle. The sbDBA concept was evaluated in Monte-Carlo (MC) simulations regarding its spectral and scattering properties. A prototype of the sbDBA was installed in a clinical CT scanner and measurements evaluating the feasibility and the performance of the sbDBA concept were carried out. RESULTS: Experimental measurements on a CT scanner demonstrate the ability of the sbDBA to produce an attenuation profile that can be changed in width and location. Furthermore, the sbDBA shows constant transmission properties at various tube voltages. A small effect of the flying focal spot (FFS) position on the transmission profile can be observed. MC simulations confirm the essential properties of the sbDBA: In contrast to conventional bowtie filters, the sbDBA has almost no impact on the energy spectrum of the beam and there is negligible scatter emission toward the patient. CONCLUSIONS: A new concept for dynamic beam attenuation has been presented and its ability to dynamically shape the transmission profile has successfully been demonstrated. Advantages compared to regular bowtie filters including the lack of filter-induced beam hardening and scatter have been confirmed. The novel concept of a DBA paves the way toward region of interest (ROI) imaging and further reductions in patient dose.


Subject(s)
Image Processing, Computer-Assisted/methods , Tomography, X-Ray Computed , Abdomen/diagnostic imaging , Humans , Monte Carlo Method , Phantoms, Imaging , Scattering, Radiation , Software
7.
Urol Pract ; 6(5): 300-308, 2019 Sep.
Article in English | MEDLINE | ID: mdl-37317340

ABSTRACT

INTRODUCTION: Since 2014 the AUA (American Urological Association) has convened several Quality Improvement Summits to provide education and promote dialogue around issues of quality improvement and patient safety. The 2017 Summit, Challenges and Opportunities for Stewardship of Urological Imaging, organized in partnership with the American College of Radiology and the American College of Emergency Physicians, highlighted opportunities for collaborative improvement in the value, safety and quality of imaging for patients with urological conditions. METHODS: The Summit was held at AUA headquarters in Linthicum, Maryland on October 21, 2017. Each talk, panel and working group held during the summit highlighted gaps in care being addressed by physician led stewardship initiatives in imaging, in general, as well as multiple specific examples related to prostate cancer and urinary stone disease. RESULTS: Presentations facilitated information exchange on quality efforts between clinicians across disciplines and care settings and served to educate urology practitioners, primary care physicians, and specialists about existing patient centered quality improvement programs. CONCLUSIONS: This exchange serves to accelerate adoption of evidence-based practices and brings together stakeholder organizations to form partnerships that facilitate the further development of research and policy agendas to advance physician led stewardship of advanced imaging across emergency medicine, radiology and urology. In parallel, this meeting established a consortium to develop and disseminate tools for facilitating organizational improvement activities needed to enhance the quality and safety of medical care.

8.
IEEE Trans Radiat Plasma Med Sci ; 3(1): 31-37, 2019 Jan.
Article in English | MEDLINE | ID: mdl-33829118

ABSTRACT

Optimal treatment planning for radioembolization of hepatic cancers produces sufficient dose to tumors for control and dose to normal liver parenchyma that is below the threshold for toxicity. The non-uniform distribution of particles in liver microanatomy complicates the planning process as different functional regions receive different doses. Having realistic and patient-specific models of the arterial tree and microsphere trapping would be useful for developing more optimal treatment plans. We propose a macrocell-based growth method to generate models of the hepatic arterial tree from the proper hepatic artery to the terminal arterioles supplying the capillaries in the parenchyma. We show how these trees can be adapted to match patient values of pressure, flow, and vessel diameters while still conforming to laws controlling vessel bifurcation, changes in pressure, and blood flow. We also introduce a method to model particle transport within the tree that accounts for vessel and particle diameter distributions and show the non-uniform microsphere deposition pattern that results. Potential applications include investigating dose heterogeneity and microsphere deposition patterns.

9.
Invest Radiol ; 53(12): 728-735, 2018 12.
Article in English | MEDLINE | ID: mdl-30015677

ABSTRACT

OBJECTIVE: The aim of this study was to compare the effects of combined virtual monoenergetic extrapolation (VME) of dual-energy computed tomography data and iterative metal artifact reduction (iMAR) at higher photon energies on low- and high-density metal artifacts and overall image quality of the ankle arthroplasty implants with iMAR, weighted filtered back projection (WFBP), and WFBP-based VME. MATERIALS AND METHODS: Total ankle arthroplasty implants in 6 human cadaver ankles served as surrogates for arthroplasty implants. All specimens underwent computed tomography with a 2 × 192-slice dual-source computed tomography scanner at tube voltages of 80 and tin-filtered 150 kVp to produce mixed 120 kVp equivalent polychromatic and virtual monoenergetic extrapolated images at 150 and 190 keV (VME 150 and VME 190, respectively). By implementing the WFBP and iMAR reconstruction algorithms on polychromatic, VME 150 and VME 190 data, 6 image datasets were created: WFBP-Polychromatic, iMAR-Polychromatic, WFBP-VME 150, WFBP-VME 190, iMAR-VME 150, and iMAR-VME 190. High-density and low-density artifacts were separately quantified with a threshold-based computer algorithm. After anonymization and randomization, 2 observers independently ranked the datasets for overall image quality. Repeated measures analysis of variance, Friedman, and Cohen weighted κ tests were applied for statistical analysis. A conservative P value of less than 0.001 was considered statistically significant. RESULTS: iMAR-VME 190 keV and iMAR-VME 150 keV created the least amount of high-density artifacts (all P < 0.001), whereas iMAR-Polychromatic was the most effective method to mitigate low-density streaks (P < 0.001). For low- and high-density artifacts, polychromatic iMAR acquisition was superior to WFBP-VME 150 keV and WFBP-VME 190 keV (all P < 0.001). On sharp kernel reconstructions, readers ranked the overall image quality of iMAR-Polychromatic images highest (all P < 0.001). Similarly, on soft tissue kernel reconstructions, readers ranked iMAR-Polychromatic images highest with a statistically significant difference over other techniques (all P < 0.001), except for iMAR-VME 150 keV (P = 0.356). CONCLUSIONS: In computed tomography imaging of ankle arthroplasty implants, iMAR reconstruction results in fewer metal artifacts and better image quality than WFBP reconstruction for both polychromatic and virtual monoenergetic data. The combination of iMAR and VME at higher photon energies results in mixed effects on implant-induced metal artifacts, including decreased high-density and increased low-density artifacts, which in combination does not improve image quality over iMAR reconstruction of the polychromatic data. Our results suggest that, for ankle arthroplasty implants, the highest image quality is obtained by iMAR reconstruction of the polychromatic data without the need to implement VME at high-energy levels.


Subject(s)
Arthroplasty, Replacement, Ankle/instrumentation , Artifacts , Image Processing, Computer-Assisted/methods , Metals , Prostheses and Implants , Tomography, X-Ray Computed/methods , Aged , Aged, 80 and over , Algorithms , Ankle Joint/diagnostic imaging , Cadaver , Female , Humans , Image Interpretation, Computer-Assisted , Male , Photons
10.
J Endourol ; 32(8): 685-691, 2018 08.
Article in English | MEDLINE | ID: mdl-29890914

ABSTRACT

INTRODUCTION: CT is the gold standard for visualizing renal and ureteral calculi. CT three-dimensional reformatting allows for automatic, accurate, and reliable measurement of stone size, volume, density, and location. In this study, we aimed to develop and test a software platform capable of calculating a battery of clinically important urinary stone parameters at the point-of-care (POC). METHODS: The syngo Calcium Scoring (Siemens Corporation) algorithm was modified to identify calcium-based stones using an attenuation threshold (250 HU) within a region of interest. Information automatically obtained after reconstruction included voxel sum and calculated volume, maximum diameter, largest diameter in the x, y, and z planes, cumulative diameter, distribution of attenuation in HU, and position relative to the skin for calculation of the skin-to-stone distance (SSD). This algorithm was packaged into a stand-alone application (MATLAB 9.1). From April 2017 to May 2017, all patients undergoing a noncontrast CT of the abdomen or the abdomen and pelvis at the Johns Hopkins Hospital were eligible for inclusion in this validation cohort. RESULTS: A total of 55 index renal stones were included. The mean volume calculated by voxel sum was 216.53 mm3 (standard deviation [SD] ±616.19, range 1.50-4060.13). The mean volume calculated using the Ackermann's formula and for a sphere was 232.96 mm3 (SD ± 702.65, range 1.24-4074.04) and 1214.63 mm3 (SD ± 4233.41, range 1.77-25,246.40), respectively. The mean largest diameter in any one direction was 6.95 mm (SD ± 7.31, range 1.50-36.40). The maximum density of the stones ranged from 164 to 1725 HU. The mean SSD at the shortest possible point was 14.19 cm (SD ± 6.13, range 6.67-31.28). CONCLUSIONS: We developed a stand-alone platform with a simple easy-to-use interface, which will allow any user the ability to calculate a battery of clinically important urinary stone parameters from CT imaging at the POC. This program is now freely available online.


Subject(s)
Image Processing, Computer-Assisted/methods , Kidney Calculi/diagnostic imaging , Tomography, X-Ray Computed , Ureteral Calculi/diagnostic imaging , Urinary Calculi/diagnostic imaging , Algorithms , Calcium , Diagnosis, Computer-Assisted/methods , Humans , Kidney , Pattern Recognition, Automated , Radiography, Abdominal , Skin/pathology , Software , User-Computer Interface
11.
IEEE Trans Med Imaging ; 37(3): 680-692, 2018 03.
Article in English | MEDLINE | ID: mdl-28809677

ABSTRACT

The four-dimensional (4-D) eXtended CArdiac-Torso (XCAT) series of phantoms was developed to provide accurate computerized models of the human anatomy and physiology. The XCAT series encompasses a vast population of phantoms of varying ages from newborn to adult, each including parameterized models for the cardiac and respiratory motions. With great flexibility in the XCAT's design, any number of body sizes, different anatomies, cardiac or respiratory motions or patterns, patient positions and orientations, and spatial resolutions can be simulated. As such, the XCAT phantoms are gaining a wide use in biomedical imaging research. There they can provide a virtual patient base from which to quantitatively evaluate and improve imaging instrumentation, data acquisition, techniques, and image reconstruction and processing methods which can lead to improved image quality and more accurate clinical diagnoses. The phantoms have also found great use in radiation dosimetry, radiation therapy, medical device design, and even the security and defense industry. This review paper highlights some specific areas in which the XCAT phantoms have found use within biomedical imaging and other fields. From these examples, we illustrate the increasingly important role that computerized phantoms and computer simulation are playing in the research community.


Subject(s)
Imaging, Three-Dimensional , Phantoms, Imaging , Tomography, X-Ray Computed , Computer Simulation , Humans , Radiometry
12.
Ann Nucl Med ; 32(2): 87-93, 2018 Feb.
Article in English | MEDLINE | ID: mdl-29214562

ABSTRACT

OBJECTIVE: Technetium-99m (99mTc)-sestamibi single-photon emission computed tomography/computed tomography (SPECT/CT) has previously been shown to allow for the accurate differentiation of benign renal oncocytomas and hybrid oncocytic/chromophobe tumors (HOCTs) apart from other malignant renal tumor histologies, with oncocytomas/HOCTs showing high uptake and renal cell carcinoma (RCC) showing low uptake based on uptake ratios from non-quantitative single-photon emission computed tomography (SPECT) reconstructions. However, in this study, several tumors fell close to the uptake ratio cutoff, likely due to limitations in conventional SPECT/CT reconstruction methods. We hypothesized that application of quantitative SPECT/CT (QSPECT) reconstruction methods developed by our group would provide more robust separation of hot and cold lesions, serving as an imaging framework on which quantitative biomarkers can be validated for evaluation of renal masses with 99mTc-sestamibi. METHODS: Single-photon emission computed tomography data were reconstructed using the clinical Flash 3D reconstruction and QSPECT methods. Two blinded readers then characterized each tumor as hot or cold. Semi-quantitative uptake ratios were calculated by dividing lesion activity by background renal activity for both Flash 3D and QSPECT reconstructions. RESULTS: The difference between median (mean) hot and cold tumor uptake ratios measured 0.655 (0.73) with the QSPECT method and 0.624 (0.67) with the conventional method, resulting in increased separation between hot and cold tumors. Sub-analysis of 7 lesions near the separation point showed a higher absolute difference (0.16) between QPSECT and Flash 3D mean uptake ratios compared to the remaining lesions. CONCLUSIONS: Our finding of improved separation between uptake ratios of hot and cold lesions using QSPECT reconstruction lays the foundation for additional quantitative SPECT techniques such as SPECT-UV in the setting of renal 99mTc-sestamibi and other SPECT/CT exams. With robust quantitative image reconstruction and biomarker analysis, there may be an expanded role for SPECT/CT imaging in renal masses and other pathologic conditions.


Subject(s)
Adenoma, Oxyphilic/diagnostic imaging , Imaging, Three-Dimensional , Kidney Neoplasms/diagnostic imaging , Single Photon Emission Computed Tomography Computed Tomography , Technetium Tc 99m Sestamibi , Adult , Aged , Aged, 80 and over , Diagnosis, Differential , Female , Humans , Male , Middle Aged
13.
Phys Med ; 42: 127-134, 2017 Oct.
Article in English | MEDLINE | ID: mdl-29173905

ABSTRACT

The new PET tracer, 18F-flurpiridaz, with high myocardial extraction allows quantitative myocardial blood flow (MBF) estimation from dynamic PET data and tracer kinetic modeling. The goal of this study is to determine the optimal imaging protocols and parameters using a realistic simulation study. The time activity curves (TACs) of different tissue organs from a 30-s infusion time (IT) of 18F-flurpiridaz in a dynamic PET study were extracted from a previous study. The TACs at different time points were incorporated in a series of realistic 3D XCAT phantoms from which the parameters of a 2-compartment model and the 'true' MBF of 18F-flurpiridaz were determined. The compartmental model was used to generate TACs from 7 additional ITs. PET projection data from the XCAT phantoms were generated using Monte Carlo simulation. They were reconstructed using an OS-EM reconstruction algorithm with different update number (N) to obtain dynamic PET images. The blood and myocardial TACs were derived from the dynamic images from which the MBF and %MBF error was estimated. The %MBF error decreases with increasing N of the OS-EM and levels off after ∼42. The 30-s IT gave the smallest %MBF error that decreases from ∼0.57% to ∼19.40%. The MBF for 2-min, 4-min, 8-min and 16-min IT were statistically significant different from the MBF for 30-s IT (P<0.05). Too fast or too slow infusion time gave higher %MBF error. The optimal imaging protocol in dynamic 18F-flurpiridaz PET for accurate quantitative MBF estimation was 30-s IT and N of ∼42 for the OS-EM.


Subject(s)
Coronary Circulation , Coronary Vessels/diagnostic imaging , Heart/diagnostic imaging , Myocardial Perfusion Imaging/methods , Positron-Emission Tomography/methods , Pyridazines , Radiopharmaceuticals , Algorithms , Animals , Computer Simulation , Coronary Vessels/physiology , Humans , Models, Biological , Monte Carlo Method , Myocardial Perfusion Imaging/instrumentation , Myocardium/metabolism , Phantoms, Imaging , Positron-Emission Tomography/instrumentation , Pyridazines/pharmacokinetics , Radiopharmaceuticals/pharmacokinetics , Regional Blood Flow , Sus scrofa , Time Factors
14.
Med Phys ; 44(9): 4677-4686, 2017 Sep.
Article in English | MEDLINE | ID: mdl-28639400

ABSTRACT

PURPOSE: This work concerns computed tomography (CT)-based cardiac functional analysis (CFA) with a reduced radiation dose. As CT-CFA requires images over the entire heartbeat, the scans are often performed at 10-20% of the tube current settings that are typically used for coronary CT angiography. A large image noise then degrades the accuracy of motion estimation. Moreover, even if the scan was performed during the sinus rhythm, the cardiac motion observed in CT images may not be cyclic with patients with atrial fibrillation. In this study, we propose to use two CT scan data, one for CT angiography at a quiescent phase at a standard dose and the other for CFA over the entire heart beat at a lower dose. METHODS: We have made the following four modifications to an image-based cardiac motion estimation method we have previously developed for a full-dose retrospectively gated coronary CT angiography: (a) a full-dose prospectively gated coronary CT angiography image acquired at the least motion phase was used as the reference image; (b) a three-dimensional median filter was applied to lower-dose retrospectively gated cardiac images acquired at 20 phases over one heartbeat in order to reduce image noise; (c) the strength of the temporal regularization term was made adaptive; and (d) a one-dimensional temporal filter was applied to the estimated motion vector field in order to decrease jaggy motion patterns. We describe the conventional method iME1 and the proposed method iME2 in this article. Five observers assessed the accuracy of the estimated motion vector field of iME2 and iME1 using a 4-point scale. The observers repeated the assessment with data presented in a new random order 1 week after the first assessment session. RESULTS: The study confirmed that the proposed iME2 was robust against the mismatch of noise levels, contrast enhancement levels, and shapes of the chambers. There was a statistically significant difference between iME2 and iME1 (accuracy score, 2.08 ± 0.81 versus 2.77 ± 0.98, P < 0.01) and the improvement by the score of + 0.69 seemed clinically relevant. Inter-observer concordance was good: The inter-class correlation coefficient was 0.63 and Kendall's rank correlation coefficients were in the range of 0.41-0.67 (P < 0.01), respectively. Intra-observer reproducibility between sessions was good with the inter-class correlation coefficient of 0.76. CONCLUSION: We have proposed iME2 method for CT-CFA with two CT scans. The observer study verified the robustness and accuracy of iME2 method and its improved performance over iME1 method.


Subject(s)
Algorithms , Coronary Angiography , Tomography, X-Ray Computed , Artifacts , Humans , Motion , Radiation Dosage , Reproducibility of Results
15.
Phys Med Biol ; 61(1): 151-68, 2016 Jan 07.
Article in English | MEDLINE | ID: mdl-26624887

ABSTRACT

Respiratory motion (RM) and cardiac motion (CM) degrade the quality and resolution in cardiac PET scans. We have developed non-rigid motion estimation methods to estimate both RM and CM based on 4D cardiac gated PET data alone, and compensate the dual respiratory and cardiac (R&C) motions after (MCAR), during (MCDR), and before (MCBR) image reconstruction. In all three R&C motion correction methods, attenuation-activity mismatch effect was modeled by using transformed attenuation maps using the estimated RM. The difference of using activity preserving and non-activity preserving models in R&C correction was also studied. Realistic Monte Carlo simulated 4D cardiac PET data using the 4D XCAT phantom and accurate models of the scanner design parameters and performance characteristics at different noise levels were employed as the known truth and for method development and evaluation. Results from the simulation study suggested that all three dual R&C motion correction methods provide substantial improvement in the quality of 4D cardiac gated PET images as compared with no motion correction. Specifically, the MCDR method yields the best performance for all different noise levels compared with the MCAR and MCBR methods. While MCBR reduces computational time dramatically but the resultant 4D cardiac gated PET images has overall inferior image quality when compared to that from the MCAR and MCDR approaches in the 'almost' noise free case. Also, the MCBR method has better noise handling properties when compared with MCAR and provides better quantitative results in high noise cases. When the goal is to reduce scan time or patient radiation dose, MCDR and MCBR provide a good compromise between image quality and computational times.


Subject(s)
Cardiac Imaging Techniques/methods , Image Processing, Computer-Assisted/methods , Positron-Emission Tomography/methods , Humans , Motion , Phantoms, Imaging , Respiration
16.
Magn Reson Med ; 76(2): 663-78, 2016 08.
Article in English | MEDLINE | ID: mdl-26479724

ABSTRACT

PURPOSE: Analytical phantoms have closed form Fourier transform expressions and are used to simulate MRI acquisitions. Existing three-dimensional (3D) analytical phantoms are unable to accurately model shapes of biomedical interest. The goal of this study was to demonstrate that polyhedral analytical phantoms have closed form Fourier transform expressions and can accurately represent 3D biomedical shapes. METHODS: The Fourier transform of a polyhedron was implemented and its accuracy in representing faceted and smooth surfaces was characterized. Realistic anthropomorphic polyhedral brain and torso phantoms were constructed and their use in simulated 3D and two-dimensional (2D) MRI acquisitions was described. RESULTS: Using polyhedra, the Fourier transform of faceted shapes can be computed to within machine precision. Smooth surfaces can be approximated with increasing accuracy by increasing the number of facets in the polyhedron; the additional accumulated numerical imprecision of the Fourier transform of polyhedra with many faces remained small. Simulations of 3D and 2D brain and 2D torso cine acquisitions produced realistic reconstructions free of high frequency edge aliasing compared with equivalent voxelized/rasterized phantoms. CONCLUSION: Analytical polyhedral phantoms are easy to construct and can accurately simulate shapes of biomedical interest. Magn Reson Med 76:663-678, 2016. © 2015 Wiley Periodicals, Inc.


Subject(s)
Biomimetics/methods , Imaging, Three-Dimensional/methods , Magnetic Resonance Imaging/methods , Models, Biological , Phantoms, Imaging , Animals , Computer Simulation , Fourier Analysis , Humans , Magnetic Resonance Imaging/instrumentation , Reproducibility of Results , Sensitivity and Specificity
17.
Med Phys ; 42(9): 5329-41, 2015 Sep.
Article in English | MEDLINE | ID: mdl-26328982

ABSTRACT

PURPOSE: Newly developed spectral computed tomography (CT) such as photon counting detector CT enables more accurate tissue-type identification through material decomposition technique. Many iterative reconstruction methods, including those developed for spectral CT, however, employ a regularization term whose penalty transition is designed using pixel value of CT image itself. Similarly, the tissue-type identification methods are then applied after reconstruction; thus, it is impossible to take into account probability distribution obtained from projection likelihood. The purpose of this work is to develop comprehensive image reconstruction and tissue-type identification algorithm which improves quality of both reconstructed image and tissue-type map. METHODS: The authors propose a new framework to jointly perform image reconstruction, material decomposition, and tissue-type identification for photon counting detector CT by applying maximum a posteriori estimation with voxel-based latent variables for the tissue types. The latent variables are treated using a voxel-based coupled Markov random field to describe the continuity and discontinuity of human organs and a set of Gaussian distributions to incorporate the statistical relation between the tissue types and their attenuation characteristics. The performance of the proposed method is quantitatively compared to that of filtered backprojection and a quadratic penalized likelihood method by 100 noise realization. RESULTS: Results showed a superior trade-off between image noise and resolution to current reconstruction methods. The standard deviation (SD) and bias of reconstructed image were improved from quadratic penalized likelihood method: bias, -0.9 vs -0.1 Hounsfield unit (HU); SD, 46.8 vs 27.4 HU. The accuracy of tissue-type identification was also improved from quadratic penalized likelihood method: 80.1% vs 86.9%. CONCLUSIONS: The proposed method makes it possible not only to identify tissue types more accurately but also to reconstruct CT images with decreased noise and enhanced sharpness owing to the information about the tissue types.


Subject(s)
Image Processing, Computer-Assisted/methods , Photons , Tomography, X-Ray Computed/methods , Humans , Phantoms, Imaging
18.
Phys Med Biol ; 60(7): 2881-901, 2015 Apr 07.
Article in English | MEDLINE | ID: mdl-25776521

ABSTRACT

Iterative reconstruction (IR) methods for x-ray CT is a promising approach to improve image quality or reduce radiation dose to patients. The goal of this work was to use task based image quality measures and the channelized Hotelling observer (CHO) to evaluate both analytic and IR methods for clinical x-ray CT applications. We performed realistic computer simulations at five radiation dose levels, from a clinical reference low dose D0 to 25% D0. A fixed size and contrast lesion was inserted at different locations into the liver of the XCAT phantom to simulate a weak signal. The simulated data were reconstructed on a commercial CT scanner (SOMATOM Definition Flash; Siemens, Forchheim, Germany) using the vendor-provided analytic (WFBP) and IR (SAFIRE) methods. The reconstructed images were analyzed by CHOs with both rotationally symmetric (RS) and rotationally oriented (RO) channels, and with different numbers of lesion locations (5, 10, and 20) in a signal known exactly (SKE), background known exactly but variable (BKEV) detection task. The area under the receiver operating characteristic curve (AUC) was used as a summary measure to compare the IR and analytic methods; the AUC was also used as the equal performance criterion to derive the potential dose reduction factor of IR. In general, there was a good agreement in the relative AUC values of different reconstruction methods using CHOs with RS and RO channels, although the CHO with RO channels achieved higher AUCs than RS channels. The improvement of IR over analytic methods depends on the dose level. The reference dose level D0 was based on a clinical low dose protocol, lower than the standard dose due to the use of IR methods. At 75% D0, the performance improvement was statistically significant (p < 0.05). The potential dose reduction factor also depended on the detection task. For the SKE/BKEV task involving 10 lesion locations, a dose reduction of at least 25% from D0 was achieved.


Subject(s)
Radiographic Image Interpretation, Computer-Assisted/methods , Tomography, X-Ray Computed/methods , Algorithms , Area Under Curve , Computer Simulation , Germany , Humans , Image Processing, Computer-Assisted , Phantoms, Imaging , ROC Curve , Radiation Dosage , Signal-To-Noise Ratio
19.
Phys Med ; 31(2): 159-66, 2015 Mar.
Article in English | MEDLINE | ID: mdl-25555904

ABSTRACT

The value of Tc-99m MIBI parathyroid SPECT for localizing parathyroid hyperplasia in chronic renal failure patients remains inconclusive due to limited image quality. Advanced reconstruction methods to improve image quality have been developed but require optimization and evaluation. The goal of this study was to optimize and evaluate compensation methods and reconstruction parameters for Tc-99m MIBI parathyroid SPECT. A phantom population and projection data that modelled clinically realistic variations found in patients were simulated. The 3D OS-EM reconstruction with compensation for attenuation, detector response and scatter in various combinations were studied. For each compensation, the number of updates for OS-EM and the cutoff frequency of a 3D Butterworth filter were optimized and evaluated using anthropomorphic model observer. With optimal parameters, the method with compensation for attenuation and detector response, with or without the addition of scatter compensation, provided the highest lesion detectability for Tc-99m MIBI parathyroid SPECT.


Subject(s)
Image Processing, Computer-Assisted/methods , Parathyroid Glands/diagnostic imaging , Technetium Tc 99m Sestamibi , Tomography, Emission-Computed, Single-Photon/methods , Area Under Curve , Female , Humans , Male , Parathyroid Diseases/diagnostic imaging , Phantoms, Imaging , ROC Curve
20.
Dysphagia ; 30(1): 47-56, 2015 Feb.
Article in English | MEDLINE | ID: mdl-25270532

ABSTRACT

The purpose was to determine the effect of bilateral superior laryngeal nerve (SLN) lesion on swallowing threshold volume and the occurrence of aspiration, using a novel measurement technique for videofluoroscopic swallowing studies (VFSS) in infant pigs. We used a novel radiographic phantom to assess volume of the milk containing barium from fluoroscopy. The custom made phantom was firstly calibrated by comparing image intensity of the phantom with known cylinder depths. Secondly, known volume pouches of milk in a pig cadaver were compared to volumes calculated with the phantom. Using these standards, we calculated the volume of milk in the valleculae, esophagus and larynx, for 205 feeding sequences from four infant pigs feeding before and after had bilateral SLN lesions. Swallow safety was assessed using the tested and validated IMPAS (Dysphagia 28(2):178-187, 2013). The log-linear correlation between image intensity values from the phantom filled with barium milk and the known phantom cylinder depths was strong (R (2) > 0.95), as was the calculated volumes of the barium milk pouches. The threshold volume of bolus in the valleculae during feeding was significantly larger after bilateral SLN lesion than in control swallows (p < 0.001). The IMPAS score increased in the lesioned swallows relative to the controls, indicating substantially impaired swallowing (p < 0.001). Bilateral SLN lesion dramatically increased the aspiration incidence and the threshold volume of bolus in valleculae. The use of this phantom permits quantification of the aspirated volume of fluid, allowing for more accurate 3D volume estimation from 2D X-ray in VFSS.


Subject(s)
Deglutition , Fluoroscopy/methods , Larynx/physiology , Animals , Calibration , Female , Fluoroscopy/instrumentation , Larynx/anatomy & histology , Swine , Video Recording
SELECTION OF CITATIONS
SEARCH DETAIL
...