Mostrar: 20 | 50 | 100
Resultados 1 - 20 de 41.801
Filtrar
Mais filtros

Assunto principal
Tipo de estudo
Idioma
Intervalo de ano de publicação
1.
Skeletal Radiol ; 52(1): 23-29, 2023 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-35831718

##### RESUMO

OBJECTIVE: To compare the image quality of ultra-high-resolution wrist CTs acquired on photon-counting detector CT versus conventional energy-integrating-detector CT systems. MATERIALS AND METHODS: Participants were scanned on a photon-counting-detector CT system after clinical energy-integrating detector CTs. Energy-integrating-detector CT scan parameters: comb filter-based ultra-high-resolution mode, 120 kV, 250 mAs, Ur70 or Ur73 kernel, 0.4- or 0.6-mm section thickness. Photon-counting-detector CT scan parameters: non-comb-based ultra-high-resolution mode, 120 kV, 120 mAs, Br84 kernel, 0.4-mm section thickness. Two musculoskeletal radiologists blinded to CT system, scored specific osseous structures using a 5-point Likert scale (1 to 5). The Wilcoxon rank-sum test was used for statistical analysis of reader scores. Paired t-test was used to compare volume CT dose index, bone CT number, and image noise between CT systems. P-value < 0.05 was considered statistically significant. RESULTS: Twelve wrists (mean participant age 55.3 ± 17.8, 6 females, 6 males) were included. The mean volume CT dose index was lower for photon-counting detector CT (9.6 ± 0.1 mGy versus 19.0 ± 6.7 mGy, p < .001). Photon-counting-detector CT images had higher Likert scores for visualization of osseous structures (median score = 4, p < 0.001). The mean bone CT number was higher in photon-counting-detector CT images (1946 ± 77 HU versus 1727 ± 49 HU, p < 0.001). Conversely, there was no difference in the mean image noise of the two CT systems (63 ± 6 HU versus 61 ± 6 HU, p = 0.13). CONCLUSION: Ultra-high-resolution imaging with photon-counting-detector CT depicted wrist structures more clearly than conventional energy-integrating-detector CT despite a 49% radiation dose reduction.

##### Assuntos
Fótons , Punho , Masculino , Feminino , Humanos , Imagens de Fantasmas , Punho/diagnóstico por imagem , Tomografia Computadorizada por Raios X/métodos , Doses de Radiação
2.
Magn Reson Med ; 89(1): 469-476, 2023 01.
Artigo em Inglês | MEDLINE | ID: mdl-36089826

##### RESUMO

PURPOSE: This study aims to find a relation between the number of channels and the computational burden for specific absorption rate (SAR) calculation using virtual observation point-based SAR compression. METHODS: Eleven different arrays of rectangular loops covering a cylinder of fixed size around the head of an anatomically correct voxel model were simulated. The resulting Q-matrices were compressed with 2 different compression algorithms, with the overestimation fixed to a certain fraction of worst-case SAR, median SAR, or minimum SAR. The latter 2 were calculated from 1e6 normalized random excitation vectors. RESULTS: The number of virtual observation points increased with the number of channels to the power of 2.3-3.7, depending on the compression algorithm when holding the relative error fixed. Together with the increase in the size of the Q-matrices (and therefore the size of the virtual observation points), the total increase in computational burden with the number of channels was to the power of 4.3-5.7. CONCLUSION: The computational cost emphasizes the need to use the best possible compression algorithms when moving to high channel counts.

##### Assuntos
Compressão de Dados , Imageamento por Ressonância Magnética , Imageamento por Ressonância Magnética/métodos , Algoritmos , Simulação por Computador , Imagens de Fantasmas
3.
Magn Reson Med ; 89(1): 192-204, 2023 01.
Artigo em Inglês | MEDLINE | ID: mdl-36093906

##### RESUMO

PURPOSE: Many MRI sequences are sensitive to motion and its associated artifacts. The linearized geometric solution (LGS), a balanced steady-state free precession (bSSFP) off-resonance signal demodulation technique, is evaluated with respect to motion artifact resilience. THEORY AND METHODS: The mechanism and extent of LGS motion artifact resilience is examined in simulated, flow phantom, and in vivo clinical imaging. Motion artifact correction capabilities are decoupled from susceptibility artifact correction when feasible to permit controlled analysis of motion artifact correction when comparing the LGS with standard and phase-cycle-averaged (complex sum) bSSFP imaging. RESULTS: Simulations reveal that the LGS demonstrates motion artifact reduction capabilities similar to standard clinical bSSFP imaging techniques, with slightly greater resilience in high SNR regions and for shorter-duration motion. Flow phantom experiments assert that the LGS reduces shorter-duration motion artifact error by â¼24%-65% relative to the complex sum, whereas reconstructions exhibit similar error reduction for constant motion. In vivo analysis demonstrates that in the internal auditory canal/orbits, the LGS was deemed to have less artifact in 24%/49% and similar artifact in 76%/51% of radiological assessments relative to the complex sum, and the LGS had less artifact in 97%/81% and similar artifact in 3%/16% of assessments relative to standard bSSFP. Only 2 of 63 assessments deemed the LGS inferior to either complex sum or standard bSSFP in terms of artifact reduction. CONCLUSION: The LGS provides sufficient bSSFP motion artifact resilience to permit robust elimination of susceptibility artifacts, inspiring its use in a wide variety of applications.

##### Assuntos
Aumento da Imagem , Interpretação de Imagem Assistida por Computador , Aumento da Imagem/métodos , Interpretação de Imagem Assistida por Computador/métodos , Algoritmos , Artefatos , Imageamento por Ressonância Magnética/métodos , Imagens de Fantasmas
4.
Magn Reson Med ; 89(1): 454-468, 2023 01.
Artigo em Inglês | MEDLINE | ID: mdl-36093998

##### RESUMO

PURPOSE: The purpose is to develop a model-based image-reconstruction method using wavelet sparsity regularization for maintaining restoration of through-plane resolution but with improved retention of SNR versus linear reconstruction using Tikhonov (TK) regularization in high through-plane resolution (1 mm) T2 -weighted spin-echo (T2SE) images of the prostate. METHODS: A wavelet sparsity (WS)-regularized image reconstruction was developed that takes as input a set of ≈80 overlapped 3-mm-thick slices acquired using a T2SE multislice scan and typically 30 coil elements. After testing in contrast and resolution phantoms and calibration in 6 subjects, the WS reconstruction was evaluated in 16 consecutive prostate T2SE MRI exams. Results reconstructed with nominal 1-mm thickness were compared with those from the TK reconstruction with the same raw data. Results were evaluated radiologically. The ratio of magnitude of prostate signal to periprostatic muscle signal was used to assess the presence of noise reduction. Technical performance was also compared with a commercial 3D-T2SE sequence. RESULTS: The new WS reconstruction was assessed as superior statistically to TK for overall SNR, contrast, and multiple evaluation criteria related to sharpness while retaining the high (1 mm) through-plane resolution. Wavelet sparsity tended to provide improved overall diagnostic quality versus TK, but not significantly so. In all 16 studies, the prostate-to-muscle signal ratio increased. CONCLUSIONS: Model-based WS-regularized reconstruction consistently provides improved SNR in high (1 mm) through-plane resolution images of prostate T2SE MRI versus linear reconstruction using TK regularization.

##### Assuntos
Imageamento por Ressonância Magnética , Próstata , Masculino , Humanos , Próstata/diagnóstico por imagem , Imageamento por Ressonância Magnética/métodos , Imagens de Fantasmas , Pelve , Processamento de Imagem Assistida por Computador/métodos
5.
Magn Reson Med ; 89(1): 286-298, 2023 01.
Artigo em Inglês | MEDLINE | ID: mdl-36121015

##### RESUMO

PURPOSE: To develop an efficient algorithm for multicomponent MR fingerprinting (MC-MRF) reconstructions directly from highly undersampled data without making prior assumptions about tissue relaxation times and expected number of tissues. METHODS: The proposed method reconstructs MC-MRF maps from highly undersampled data by iteratively applying a joint-sparsity constraint to the estimated tissue components. Intermediate component maps are obtained by a low-rank multicomponent alternating direction method of multipliers (MC-ADMM) including the non-negativity of tissue weights as an extra regularization term. Over iterations, the used dictionary compression is adjusted. The proposed method (k-SPIJN) is compared with a two-step approach in which image reconstruction and multicomponent estimations are performed sequentially and tested in numerical simulations and in vivo by applying different undersampling factors in eight healthy volunteers. In the latter case, fully sampled data serves as the reference. RESULTS: The proposed method shows improved precision and accuracy in simulations compared with a state-of-art sequential approach. Obtained in vivo magnetization fraction maps for different tissue types show reduced systematic errors and reduced noise-like effects. Root mean square errors in estimated magnetization fraction maps significantly reduce from 13.0% ± $$\pm$$ 5.8% with the conventional, two-step approach to 9.6% ± $$\pm$$ 3.9% and 9.6% ± $$\pm$$ 3.2% with the proposed MC-ADMM and k-SPIJN methods, respectively. Mean standard deviation in homogeneous white matter regions reduced significantly from 8.6% to 2.9% (two step vs. k-SPIJN). CONCLUSION: The proposed MC-ADMM and k-SPIJN reconstruction methods estimate MC-MRF maps from highly undersampled data resulting in improved image quality compared with the existing method.

##### Assuntos
Compressão de Dados , Processamento de Imagem Assistida por Computador , Humanos , Processamento de Imagem Assistida por Computador/métodos , Imagens de Fantasmas , Encéfalo/diagnóstico por imagem , Imageamento por Ressonância Magnética/métodos , Compressão de Dados/métodos , Algoritmos
6.
Magn Reson Med ; 89(1): 322-330, 2023 01.
Artigo em Inglês | MEDLINE | ID: mdl-36120984

##### RESUMO

PURPOSE: To evaluate the usage of three-dimensional (3D) presaturated TurboFLASH (satTFL) for B 1 + $${\mathrm{B}}_1^{+}$$ and B 0 $${\mathrm{B}}_0$$ mapping on single channel and parallel transmission (pTx) systems. METHODS: B 1 + $${\mathrm{B}}_1^{+}$$ maps recorded with 3D satTFL were compared to maps from three other 3D B 1 + $${\mathrm{B}}_1^{+}$$ mapping sequences in an agar phantom. Furthermore, individual-channel B 1 + $${\mathrm{B}}_1^{+}$$ maps of 18 human subjects were recorded with 3D satTFL using B 1 + $${\mathrm{B}}_1^{+}$$ interferometry. A neural network was trained for masking of the maps. RESULTS: Out of the sequences compared satTFL was the only one with a mapping range exceeding well over 90°. In regions with lower flip angles there was high correspondence between satTFL and AFI. DREAM and double angle method also showed high qualitative similarity, however the magnitude differed from the other two measurements. The individual-channel B 1 + $${\mathrm{B}}_1^{+}$$ maps were successfully used for pTx pulse calculation in a separate study. CONCLUSION: 3D satTFL can record high-quality B 1 + $${\mathrm{B}}_1^{+}$$ maps with a high dynamic range in a short time. Correspondence with AFI maps is high, while measurement duration is reduced drastically.

##### Assuntos
Algoritmos , Imageamento por Ressonância Magnética , Humanos , Imageamento por Ressonância Magnética/métodos , Fluxo de Trabalho , Imagens de Fantasmas , Encéfalo
7.
Magn Reson Med ; 89(1): 262-275, 2023 01.
Artigo em Inglês | MEDLINE | ID: mdl-36129000

##### RESUMO

PURPOSE: Asymmetric gradient coils introduce zeroth- and first-order concomitant field terms, in addition to higher-order terms common to both asymmetric and symmetric gradients. Salient to compensation strategies is the accurate calibration of the concomitant field spatial offset parameters for asymmetric coils. A method that allows for one-time calibration of the offset parameters is described. THEORY AND METHODS: A modified phase contrast pulse sequence with single-sided bipolar flow encoding is proposed to calibrate the offsets for asymmetric, transverse gradient coils. By fitting the measured phase offsets to different gradient amplitudes, the spatial offsets were calculated by fitting the phase variation. This was used for calibrating real-time pre-emphasis compensation of the zeroth- and first-order concomitant fields. RESULTS: Image quality improvement with the proposed corrections was demonstrated in phantom and healthy volunteers with non-Cartesian and Cartesian trajectory acquisitions. Concomitant field compensation using the calibrated offsets resulted in a residual phase error <3% at the highest gradient amplitude and demonstrated substantial reduction of image blur and slice position/selection artifacts. CONCLUSIONS: The proposed implementation provides an accurate method for calibrating spatial offsets that can be used for real-time concomitant field compensation of zeroth and first-order terms, substantially reducing artifacts without retrospective correction or sequence specific waveform modifications.

##### Assuntos
Processamento de Imagem Assistida por Computador , Imageamento por Ressonância Magnética , Humanos , Processamento de Imagem Assistida por Computador/métodos , Calibragem , Estudos Retrospectivos , Imageamento por Ressonância Magnética/métodos , Artefatos , Imagens de Fantasmas
8.
Magn Reson Med ; 89(1): 217-232, 2023 01.
Artigo em Inglês | MEDLINE | ID: mdl-36198014

##### RESUMO

PURPOSE: To introduce non-rigid cardiac motion correction into a novel free-running framework for the simultaneous acquisition of 3D whole-heart myocardial T 1 $${T}_1$$ and T 2 $${T}_2$$ maps and cine images, enabling a â¼ $$\sim$$ 3-min scan. METHODS: Data were acquired using a free-running 3D golden-angle radial readout interleaved with inversion recovery and T 2 $${T}_2$$ -preparation pulses. After correction for translational respiratory motion, non-rigid cardiac-motion-corrected reconstruction with dictionary-based low-rank compression and patch-based regularization enabled 3D whole-heart T 1 $${T}_1$$ and T 2 $${T}_2$$ mapping at any given cardiac phase as well as whole-heart cardiac cine imaging. The framework was validated and compared with established methods in 11 healthy subjects. RESULTS: Good quality 3D T 1 $${T}_1$$ and T 2 $${T}_2$$ maps and cine images were reconstructed for all subjects. Septal T 1 $${T}_1$$ values using the proposed approach ( 1200 ± 50 $$1200\pm 50$$ ms) were higher than those from a 2D MOLLI sequence ( 1063 ± 33 $$1063\pm 33$$ ms), which is known to underestimate T 1 $${T}_1$$ , while T 2 $${T}_2$$ values from the proposed approach ( 51 ± 4 $$51\pm 4$$ ms) were in good agreement with those from a 2D GraSE sequence ( 51 ± 2 $$51\pm 2$$ ms). CONCLUSION: The proposed technique provides 3D T 1 $${T}_1$$ and T 2 $${T}_2$$ maps and cine images with isotropic spatial resolution in a single â¼ $$\sim$$ 3.3-min scan.

##### Assuntos
Imageamento Tridimensional , Imagem Cinética por Ressonância Magnética , Humanos , Imagem Cinética por Ressonância Magnética/métodos , Imageamento Tridimensional/métodos , Coração/diagnóstico por imagem , Miocárdio , Movimento (Física) , Reprodutibilidade dos Testes , Imageamento por Ressonância Magnética , Imagens de Fantasmas
9.
Magn Reson Med ; 89(1): 233-249, 2023 01.
Artigo em Inglês | MEDLINE | ID: mdl-36128888

##### RESUMO

PURPOSE: To develop a clinical CEST MR fingerprinting (CEST-MRF) method for brain tumor quantification using EPI acquisition and deep learning reconstruction. METHODS: A CEST-MRF pulse sequence originally designed for animal imaging was modified to conform to hardware limits on clinical scanners while keeping scan time under 2 min. Quantitative MRF reconstruction was performed using a deep reconstruction network (DRONE) to yield the water relaxation and chemical exchange parameters. The feasibility of the six parameter DRONE reconstruction was tested in simulations using a digital brain phantom. A healthy subject was scanned with the CEST-MRF sequence, conventional MRF and CEST sequences for comparison. Reproducibility was assessed via test-retest experiments and the concordance correlation coefficient calculated for white matter and gray matter. The clinical utility of CEST-MRF was demonstrated on four patients with brain metastases in comparison to standard clinical imaging sequences. Tumors were segmented into edema, solid core, and necrotic core regions and the CEST-MRF values compared to the contra-lateral side. RESULTS: DRONE reconstruction of the digital phantom yielded a normalized RMS error of ≤7% for all parameters. The CEST-MRF parameters were in good agreement with those from conventional MRF and CEST sequences and previous studies. The mean concordance correlation coefficient for all six parameters was 0.98 ± 0.01 in white matter and 0.98 ± 0.02 in gray matter. The CEST-MRF values in nearly all tumor regions were significantly different (P = 0.05) from each other and the contra-lateral side. CONCLUSION: Combination of EPI readout and deep learning reconstruction enabled fast, accurate and reproducible CEST-MRF in brain tumors.

##### Assuntos
Neoplasias Encefálicas , Aprendizado Profundo , Animais , Reprodutibilidade dos Testes , Imageamento por Ressonância Magnética/métodos , Encéfalo/diagnóstico por imagem , Neoplasias Encefálicas/diagnóstico por imagem , Imagens de Fantasmas , Processamento de Imagem Assistida por Computador/métodos
10.
Ultrasonics ; 127: 106833, 2023 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-36070635

##### RESUMO

High-frame-rate plane wave (PW) imaging suffers from unsatisfactory image quality due to the absence of focus in transmission. Although coherent compounding from tens of PWs can improve PW image quality, it in turn results in a decreased frame rate, which is limited for tracking fast moving tissues. To overcome the trade-off between frame rate and image quality, we propose a progressively dual reconstruction network (PDRN) to achieve adaptive beamforming and enhance the image quality via both supervised and transfer learning in the condition of single or a few PWs transmission. Specifically, the proposed model contains a progressive network and a dual network to form a close loop and provide collaborative supervision for model optimization. The progressive network takes the channel delay of each spatial point as input and progressively learns coherent compounding beamformed data with increased numbers of steered PWs step by step. The dual network learns the downsampling process and reconstructs the beamformed data with decreased numbers of steered PWs, which reduces the space of the possible learning functions and improves the model's discriminative ability. In addition, the dual network is leveraged to perform transfer learning for the training data without sufficient steered PWs. The simulated, in vivo, vocal cords (VCs), and public available CUBDL dataset are collected for model evaluation.

##### Assuntos
Processamento de Imagem Assistida por Computador , Processamento de Imagem Assistida por Computador/métodos , Imagens de Fantasmas , Ultrassonografia/métodos
11.
Ultrasonics ; 127: 106837, 2023 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-36075161

##### RESUMO

In this article, a novel ultrasound computed tomography (USCT) reconstruction algorithm for breast imaging is proposed. This algorithm is based on an ultrasound propagation model, the refract-ray model (RRM). In this model, the field of imaging is assumed as piecewise homogenous and is divided into several regions. The ultrasound propagation paths are considered polylines that only refract at the borders of the regions. The edge information is provided by B-mode imaging. Both simulations and experiments are implemented to validate the proposed algorithm. Compared with the traditional bent-ray model (BRM), the time of reconstructions using RRM decreases by over 90 %. In simulations, the imaging qualities for RRM and BRM are comparable, in terms of the root mean square error, the Tenengrad value, and the deformation of digital phantom. In the experiments, a cylindrical agar phantom is imaged using a customized imaging system. When imaging using RRM, the estimate of the phantom radius is about 0.1 mm in error, while it is about 0.3 mm in error using BRM. Moreover, the Tenengrad value of the result using RRM is much higher than that using BRM (9.76 compared to 0.79). The results show that the proposed algorithm can better delineate the phantom within a water bath. In future work, further experimental work is required to validate the method for improving imaging quality under breast-mimicking imaging conditions.

##### Assuntos
Processamento de Imagem Assistida por Computador , Tomografia Computadorizada por Raios X , Ágar , Algoritmos , Processamento de Imagem Assistida por Computador/métodos , Imagens de Fantasmas , Tomografia Computadorizada por Raios X/métodos , Água
12.
Ultrasonics ; 127: 106838, 2023 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-36126437

##### RESUMO

Coherent plane-wave compounding (CPWC) is a widely used technique in medical ultrasound imaging due to its high frame rate property. It is well-known that increasing the plane waves leads to improving the image quality. However, the image quality still needs to be further improved in CPWC. In this regard, a variety of methods have been proposed. In this paper, a new compressive sensing (CS) based approach is introduced with the combination of the adaptive minimum variance (MV) algorithm to further improve the image quality in terms of resolution and contrast. In the proposed method, which is called the CS-based MV technique, the CS method is used in the receive direction to produce the beamformed data for each plane wave. Then, the MV algorithm is performed in the plane wave transmit angle direction to coherently compound the images and improve the resolution. Moreover, to deal with the high computational complexity and also, the needing for high memory space during the CS method implementation, an approximation is considered which results in considerably reduced computational burden and memory space. The results obtained from the simulated point targets show that the proposed method leads to resolution improvement for about 71%, 5.5%, and 37% respectively, compared to DAS, DAS+MV, and CS+DAS beamformers. Also, the quantitative results obtained from the experimental contrast phantom in plane wave imaging challenge in medical ultrasound (PICMUS) data show a 3.02 dB, 2.57 dB, and 2.24 dB improvement of the contrast ratio metric using the proposed method compared to DAS, DAS+MV, and double-MV methods, respectively, indicating the good performance of the proposed method in image quality improvement.

##### Assuntos
Algoritmos , Compressão de Dados , Ácido 4-Acetamido-4'-isotiocianatostilbeno-2,2'-dissulfônico/análogos & derivados , Processamento de Imagem Assistida por Computador/métodos , Imagens de Fantasmas , Ultrassonografia/métodos
13.
Appl Radiat Isot ; 191: 110526, 2023 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-36401987

##### RESUMO

The radiopharmaceuticals most commonly used in nuclear medicine are 18F-FDG and 99mTc-DMSA, both of which are administered to paediatric and adult patients using the same time activity coefficient. However, the IAEA recommends specific paediatric dosimetry. The aim of this work (TW) was to estimate the absorbed dose for 18F-FDG and 99mTc-DMSA using two paediatric voxel phantoms (Baby and Child) by Monte Carlo techniques. Biokinetic data for both radiopharmaceuticals were obtained from ICRP 128. In addition, the new time-integrated activity coefficient (TIAC) values from a recent publication were examined for the following organs: Brain, urinary bladder wall, liver, heart wall, and lung. The absorbed dose per injected activity (AD/IA) and effective dose per injected activity (E/IA) values were calculated for both phantoms and the results were compared with simulated data of paediatric phantoms from ICRP 128, MIRDcalc software and available literature. Regarding AD/IA in organs, differences of up to 61% and 115% were found for the Baby phantom and 120% and 167% for the Child phantom using 18F-FDG and 99mTc-DMSA, respectively. For FDG using the new TIAC, a maximum difference of 244% was observed. For E/IA, the maximum differences were 27% and 31% for the Baby and Child phantoms, respectively, for FDG and DSMA. In this study, new dosimetric data were calculated using Baby and Child phantoms and the newly recommended TIAC.

##### Assuntos
Fluordesoxiglucose F18 , Compostos Radiofarmacêuticos , Adulto , Lactente , Humanos , Criança , Método de Monte Carlo , Imagens de Fantasmas , Succímero
14.
Ultrasound Med Biol ; 49(1): 186-202, 2023 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-36441029

##### RESUMO

Amplitude modulation (AM) suppresses tissue signals and detects microbubble signals in contrast-enhanced ultrasound (CEUS) and is often implemented with checkerboard apertures. However, possible crosstalk between transmitting and non-transmitting array elements may compromise tissue suppression in AM. Using AM aperture patterns other than the conventional checkerboard approach (one on, one off) may reduce the degree of crosstalk and increase the contrast-to-tissue-ratio (CTR) compared with conventional AM. Furthermore, previous studies have reported that the phase difference between the echoes in AM pulsing sequences may be used to segment tissue and microbubbles and improve tissue signal suppression and the CTR of CEUS images. However, the CTR of the image produced by alternative AM aperture patterns and the effect of segmentation approach on these alternative apertures have not been investigated. We evaluated a number of AM aperture patterns to find an optimal AM aperture pattern that provides the highest CTR. We found that the aperture that uses alternating groups of two elements, AM2, had the highest CTR for the probe evaluated. In addition, a segmentation technique based on echo phase differences (between the full and half-pulses, ΔΦAM, between the complementary half-pulses, ΔΦhalf, and the maximum of the two ΔΦmax) was also considered in the AM aperture optimization process. The segmentation approach increases the CTR by about 25 dB for all apertures. Finally, AM2 segmented with ΔΦmax had a 7-dB higher CTR in a flow phantom and a 6-dB higher contrast in a perfused pig liver than conventional AM segmented with ΔΦAM, and it is the optimal transmit aperture design.

##### Assuntos
Fígado , Microbolhas , Animais , Suínos , Ultrassonografia , Imagens de Fantasmas , Fígado/diagnóstico por imagem
15.
Ultrasound Med Biol ; 49(1): 318-332, 2023 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-36441033

##### RESUMO

Methods for patient-specific abdominal aortic aneurysm (AAA) progression monitoring and rupture risk assessment are widely investigated. Three-dimensional ultrasound can visualize the AAA's complex geometry and displacement fields. However, ultrasound has a limited field of view and low frame rate (i.e., 3-8 Hz). This article describes an approach to enhance the temporal resolution and the field of view. First, the frame rate was increased for each data set by sequencing multiple blood pulse cycles into one cycle. The sequencing method uses the original frame rate and the estimated pulse wave rate obtained from AAA distension curves. Second, the temporal registration was applied to multi-perspective acquisitions of the same AAA. Third, the field of view was increased through spatial registration and fusion using an image feature-based phase-only correlation method and a wavelet transform, respectively. Temporal sequencing was fully correct in aortic phantoms and was successful in 51 of 62 AAA patients, yielding a factor 5 frame rate increase. Spatial registration of proximal and distal ultrasound acquisitions was successful in 32 of 37 different AAA patients, based on the comparison between the fused ultrasound and computed tomography segmentation (95th percentile Haussdorf distances and similarity indices of 4.2 ± 1.7 mm and 0.92 ± 0.02 mm, respectively). Furthermore, the field of view was enlarged by 9%-49%.

##### Assuntos
Aneurisma da Aorta Abdominal , Humanos , Aneurisma da Aorta Abdominal/diagnóstico por imagem , Ultrassonografia , Imagens de Fantasmas , Tomografia Computadorizada por Raios X , Análise de Ondaletas
16.
Ultrasound Med Biol ; 49(1): 269-277, 2023 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-36441031

##### RESUMO

High-intensity focused ultrasound (HIFU) transducer acoustic output can vary over time as a result of an inconsistent power supply, damage to the transducer or deterioration over time. Therefore, easy implementation of a daily quality assurance (DQA) method is of great importance for pre-clinical research and clinical applications. We present here a thermochromic material-based phantom validated by thermal simulations and found to provide repeatable visual power output assessments in fewer than 15 s that are accurate to within 10%. Whereas current available methods such as radiation force balance measurements provide an estimate of the total acoustic power, we explain here that the thermochromic phantom is sensitive to the shape of the acoustic field at focus by changing the aperture of a multi-element transducer with a fixed acoustic power. The proposed phantom allows the end user to visually assess the transducer's functionality without resorting to expensive, time-consuming hydrophone measurements or image analysis.

##### Assuntos
Terapia por Ultrassom , Imagens de Fantasmas , Transdutores , Acústica , Processamento de Imagem Assistida por Computador
17.
Ultrasonics ; 128: 106861, 2023 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-36283264

##### RESUMO

Carotid atherosclerotic plaque composition may be an important indication of patient risk for future cerebrovascular events. Ultrasound spectral analysis has the potential to provide a robust measure of plaque composition in vivo if the backscatter transfer function can be sufficiently isolated from the effects of attenuation from overlying tissue, receive and transmit transfer functions from the ultrasound system and transducer, and diffraction. This study examines the usefulness of the nonlinearly generated second harmonic portion of the backscatter signal and the effects of a variety of attenuation compensation techniques for noninvasively characterizing human carotid plaque using spectral analysis and machine learning. Post-beamformed ultrasound backscatter radiofrequency (RF) data were acquired from 6 normal subjects and 119 carotid endarterectomy patients prior to surgery. Plaque obtained following surgery was histologically processed, and regions of interest (ROI) corresponding to homogenous tissue types (fibrous/fibro-lipidic, hemorrhagic and/or necrotic core and calcified) were selected from RF data. Both the harmonic and fundamental power spectra for each ROI was obtained and normalized by data from a uniform phantom (0.5 dB/cm-MHz slope of attenuation). Additional attenuation compensation approaches were compared to simply using the reference phantom: (1) optimum power spectral shift estimation, (2) one-step adventitial, or (3) two-step adventitial. Spectral parameters extracted from both the fundamental and harmonic estimates of the backscatter transfer function of 363 ROI's from 152 plaque specimens were used to train and test random forest and support vector machine classification models. The best results came from using spectral parameters derived from both the fundamental and second harmonic bands with a predictive accuracy of 65-68%, kappa statistic of 0.49-0.54, and accuracies of 84% for fibrous, 68-74% for hemorrhagic and/or necrotic core, and 78-81% for calcified ROI's. The result indicated that the nonlinearly generated second harmonic portion of backscatter is useful for carotid plaque tissue characterization and that a reference phantom approach with a 0.5 dB/cm-MHz slope of attenuation works as well as more complicated approaches.

##### Assuntos
Placa Aterosclerótica , Humanos , Placa Aterosclerótica/diagnóstico por imagem , Ultrassonografia/métodos , Imagens de Fantasmas , Artérias Carótidas/diagnóstico por imagem , Transdutores
18.
Ultrasonics ; 128: 106864, 2023 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-36308794

##### RESUMO

Unified pixel-based (PB) beamforming has been implemented for ultrasound imaging, offering significant enhancements in lateral resolution compared to the conventional dynamic focusing. However, it still suffers from clutter and off-axis artifacts, limiting the contrast resolution. This paper proposes an efficient method to improve image quality by integrating filtered delay multiply and sum (F-DMAS) into the framework. This hybrid strategy incorporates the spatial coherence of the received data into the beamforming process to improve contrast resolution and clutter rejection in the generated image. We also integrate a Wiener filter to suppress the spatiotemporal spreading using signals echoed from a single scatterer at the transmit focus as a kernel for the deconvolution. The Wiener filter is applied to the received waveforms before performing the hybrid strategy. The Wiener filter is shown to reduce interference due to the interaction between the excitation pulse and the transfer functions of the transducer elements, thus benefiting the axial resolution of the generated images. We validate the proposed method and compare it with other beamforming strategies through a series of experiments, including simulation, phantom, and in vivo studies. The results show that our approach can substantially improve both spatial resolution and contrast over the unified PB algorithm, while still maintaining the good features of this beamformer. The simplicity and good performance of our method show its potential for use in clinical applications.

##### Assuntos
Algoritmos , Processamento de Imagem Assistida por Computador , Processamento de Imagem Assistida por Computador/métodos , Ultrassonografia/métodos , Imagens de Fantasmas , Artefatos
19.
Ultrasonics ; 128: 106881, 2023 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-36323058

##### RESUMO

Total focusing method (TFM) attracts much interest because of high image resolution and large inspection coverage. However, the synthetic focusing approach based on delay-and-sum beamforming employs only the defect information contained in the dataset while ignoring the spatial information of the array signals, leading to limited imaging performance mixed with artifacts and noise. In addition, the signal-to-noise ratio (SNR) suffers due to single-element emission of full matrix capture. This work combines a modified delay-multiply-and-sum (DMAS) beamforming approach with conventional synthetic focusing in the TFM algorithm, to achieve optimization of TFM imaging performance. DMAS-based TFM is able to take full advantage of the defect and spatial information in the array dataset, and to generate new frequency components for better image reconstruction. As demonstrated on a series of comparative simulation and experimental results, the imaging results of the optimized TFM provide a considerable improvement in SNR. Better lateral spatial resolution is also achieved due to the increased number of equivalent transducer elements and second harmonic component. Therefore, this work provides a quite promising alternative solution for the post-processing of ultrasonic phased array with improved imaging performance.

##### Assuntos
Algoritmos , Processamento de Imagem Assistida por Computador , Imagens de Fantasmas , Ultrassonografia/métodos , Razão Sinal-Ruído , Processamento de Imagem Assistida por Computador/métodos
20.
Ultrasound Med Biol ; 49(1): 289-308, 2023 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-36283938

##### RESUMO

Shear wave velocity (SWV) reconstruction based on time-of-flight (TOF) is widely adopted to realize shear wave elasticity imaging (SWEI). It typically breaks down the reconstruction of a SWV image into many kernels and treats them independently. We hypothesized that information exchange among kernels improves the performance of SWEI. Therefore, we propose the approach of iterative re-weighted least squares based on inter-kernel communication (IKC-IRLS). We also hypothesized that time-to-peak (TTP) is superior to cross-correlation (CC) in visualizing small targets because TTP uses higher shear wave frequencies than CC. To examine the hypotheses, IKC-IRLS was combined with TTP data and compared with four established methods. The five methods were tested by imaging several small-size stiff targets (2.5, 4.0 and 6.4 mm in diameter) using different kernel sizes in the simulation and real experiments. The results indicate that the IKC-IRLS approach can mitigate speckle noise and is robust to TTP outliers. Consequently, the proposed method achieves the highest contrast-to-noise ratio and the lowest mean absolute percentage error of target in almost all tested cases.