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BACKGROUND: In modern positron emission tomography (PET) with multi-modality imaging (e.g., PET/CT and PET/MR), the attenuation correction (AC) is the single largest correction factor for image reconstruction. One way to assess AC methods and other reconstruction parameters is to utilize software-based simulation tools, such as a lesion insertion tool. Extensive validation of these simulation tools is required to ensure results of the study are clinically meaningful. PURPOSE: To evaluate different PET AC methods using a synthetic lesion insertion tool that simulates lesions in a patient cohort that has both PET/MR and PET/CT images. To further demonstrate how lesion insertion tool may be used to extend knowledge of PET reconstruction parameters, including but not limited to AC. METHODS: Lesion quantitation is compared using conventional Dixon-based MR-based AC (MRAC) to that of using CT-based AC (CTAC, a "ground truth"). First, the pre-existing lesions were simulated in a similar environment; a total of 71 lesions were identified in 18 pelvic PET/MR patient images acquired with a time-of-flight simultaneous PET/MR scanner, and matched lesions were inserted contralaterally on the same axial slice. Second, synthetic lesions were inserted into four anatomic target locations in a cohort of four patients who didn't have any observed clinical lesions in the pelvis. RESULTS: The matched lesion insertions resulted in unity between the lesion error ratios (mean SUVs), demonstrating that the inserted lesions successfully simulated the original lesions. In the second study, the inserted lesions had distinct characteristics by target locations and demonstrated negative max-SUV%diff trends for bone-dominant sites across the patient cohort. CONCLUSIONS: The current work demonstrates that the applied lesion insertion tool can simulate uptake in pelvic lesions and their expected SUV values, and that the lesion insertion tool can be extended to evaluate further PET reconstruction corrections and algorithms and their impact on quantitation accuracy and precision.
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PURPOSE: The purpose of this study is to characterize the dosimetric properties of a commercial brass GRID collimator for high energy photon beams including 15 and 10 MV. Then, the difference in dosimetric parameters of GRID beams among different energies and linacs was evaluated. METHOD: A water tank scanning system was used to acquire the dosimetric parameters, including the percentage depth dose (PDD), beam profiles, peak to valley dose ratios (PVDRs), and output factors (OFs). The profiles at various depths were measured at 100 cm source to surface distance (SSD), and field sizes of 10 × 10 cm2 and 20 × 20 cm2 on three linacs. The PVDRs and OFs were measured and compared with the treatment planning system (TPS) calculations. RESULTS: Compared with the open beam data, there were noticeable changes in PDDs of GRID fields across all the energies. The GRID fields demonstrated a maximal of 3 mm shift in dmax (Truebeam STX, 15MV, 10 × 10 cm2). The PVDR decreased as beam energy increases. The difference in PVDRs between Trilogy and Truebeam STx using 6MV and 15MV was 1.5% ± 4.0% and 2.1% ± 4.3%, respectively. However, two Truebeam linacs demonstrated less than 2% difference in PVDRs. The OF of the GRID field was dependent on the energy and field size. The measured PDDs, PVDRs, and OFs agreed with the TPS calculations within 3% difference. The TPS calculations agreed with the measurements when using 1 mm calculation resolution. CONCLUSION: The dosimetric characteristics of high-energy GRID fields, especially PVDR, significantly differ from those of low-energy GRID fields. Two Truebeam machines are interchangeable for GRID therapy, while a pronounced difference was observed between Truebeam and Trilogy. A series of empirical equations and reference look-up tables for GRID therapy can be generated to facilitate clinical applications.
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Neoplasias , Aceleradores de Partículas , Fótons , Radiometria , Dosagem Radioterapêutica , Planejamento da Radioterapia Assistida por Computador , Humanos , Planejamento da Radioterapia Assistida por Computador/métodos , Aceleradores de Partículas/instrumentação , Radiometria/métodos , Radiometria/instrumentação , Neoplasias/radioterapia , Radioterapia de Intensidade Modulada/métodos , Imagens de Fantasmas , Fracionamento da Dose de Radiação , Método de Monte CarloRESUMO
PURPOSE: The diagnostic gold standard for nonalcoholic fatty liver disease is an invasive biopsy. Noninvasive Cartesian MRI fat quantification remains limited to a breath-hold (BH). In this work, a novel free-breathing 3D stack-of-radial (FB radial) liver fat quantification technique is developed and evaluated in a preliminary study. METHODS: Phantoms and healthy subjects (n = 11) were imaged at 3 Tesla. The proton-density fat fraction (PDFF) determined using FB radial (with and without scan acceleration) was compared to BH single-voxel MR spectroscopy (SVS) and BH 3D Cartesian MRI using linear regression (correlation coefficient ρ and concordance coefficient ρc ) and Bland-Altman analysis. RESULTS: In phantoms, PDFF showed significant correlation (ρ > 0.998, ρc > 0.995) and absolute mean differences < 2.2% between FB radial and BH SVS, as well as significant correlation (ρ > 0.999, ρc > 0.998) and absolute mean differences < 0.6% between FB radial and BH Cartesian. In the liver and abdomen, PDFF showed significant correlation (ρ > 0.986, ρc > 0.985) and absolute mean differences < 1% between FB radial and BH SVS, as well as significant correlation (ρ > 0.996, ρc > 0.995) and absolute mean differences < 0.9% between FB radial and BH Cartesian. CONCLUSION: Accurate 3D liver fat quantification can be performed in 1 to 2 min using a novel FB radial technique. Magn Reson Med 79:370-382, 2018. © 2017 International Society for Magnetic Resonance in Medicine.
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Tecido Adiposo/diagnóstico por imagem , Interpretação de Imagem Assistida por Computador , Imageamento Tridimensional/métodos , Fígado/diagnóstico por imagem , Imageamento por Ressonância Magnética/métodos , Adulto , Algoritmos , Calibragem , Feminino , Humanos , Processamento de Imagem Assistida por Computador , Fígado/patologia , Masculino , Modelos Estatísticos , Hepatopatia Gordurosa não Alcoólica/patologia , Pelve/diagnóstico por imagem , Imagens de Fantasmas , Valores de Referência , RespiraçãoRESUMO
PURPOSE: Treatments using high-intensity focused ultrasound (HIFU) in the abdominal region remain challenging as a result of respiratory organ motion. A novel method is described here to achieve 3D motion-compensated ultrasound (US) MR-guided HIFU therapy using simultaneous ultrasound and MRI. METHODS: A truly hybrid US-MR-guided HIFU method was used to plan and control the treatment. Two-dimensional ultrasound was used in real time to enable tracking of the motion in the coronal plane, whereas an MR pencil-beam navigator was used to detect anterior-posterior motion. Prospective motion compensation of proton resonance frequency shift (PRFS) thermometry and HIFU electronic beam steering were achieved. RESULTS: The 3D prospective motion-corrected PRFS temperature maps showed reduced intrascan ghosting artifacts, a high signal-to-noise ratio, and low geometric distortion. The k-space data yielded a consistent temperature-dependent PRFS effect, matching the gold standard thermometry within approximately 1°C. The maximum in-plane temperature elevation ex vivo was improved by a factor of 2. Baseline thermometry acquired in volunteers indicated reduction of residual motion, together with an accuracy/precision of near-harmonic referenceless PRFS thermometry on the order of 0.5/1.0°C. CONCLUSIONS: Hybrid US-MR-guided HIFU ablation with 3D motion compensation was demonstrated ex vivo together with a stable referenceless PRFS thermometry baseline in healthy volunteer liver acquisitions. Magn Reson Med 79:2511-2523, 2018. © 2017 International Society for Magnetic Resonance in Medicine.
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Ablação por Ultrassom Focalizado de Alta Intensidade/métodos , Imageamento Tridimensional/métodos , Imageamento por Ressonância Magnética/métodos , Cirurgia Assistida por Computador/métodos , Adulto , Algoritmos , Animais , Bovinos , Feminino , Humanos , Fígado/diagnóstico por imagem , Fígado/cirurgia , Masculino , Termometria/métodosRESUMO
PURPOSE: Three-dimensional (3D) dark-blood MRI has shown great potential in coronary artery plaque evaluation. However, substantial variability in quantification could result from superficial calcification because of its low signal. To address this issue, a 3D coronary dark-blood interleaved with gray-blood (cDIG) technique was developed. METHODS: cDIG is based on a balanced steady-state free precession readout combined with a local re-inversion-based double-inversion-recovery (LocReInv-DIR) preparation. The LocReInv-DIR is applied every two RR intervals. Dark-blood and gray-blood contrasts are collected in the first and second RR interval, respectively. To improve the respiratory gating efficiency, two independent navigators were developed to separately gate the respiratory motion for the two interleaved acquisitions. In vivo experiments in eight healthy subjects and one patient were conducted to validate the technique. RESULTS: cDIG provided dual-contrasts without compromise in scan time. The dark-blood images with cDIG demonstrated excellent wall and lumen signal performances and morphological measurements. Advantageously, cDIG yielded a second contrast that was shown to help identify the superficial calcification in the coronary plaque of a patient. CONCLUSION: A novel technique was developed for obtaining 3D coronary vessel wall and gray lumen images. The additional contrast may aid in identifying calcified nodules and thus potentially improve the evaluation of coronary plaque burden.
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Imageamento Tridimensional/métodos , Imageamento por Ressonância Magnética/métodos , Adulto , Simulação por Computador , Vasos Coronários/fisiologia , Feminino , Humanos , Masculino , Pessoa de Meia-IdadeRESUMO
PURPOSE: To develop a respiratory self-gating method, adaptive online self-gating (ADIOS), for noncontrast MR angiography (NC MRA) of renal arteries to overcome some limitations of current free-breathing methods. METHODS: A NC MRA pulse sequence for online respiratory self-gating was developed based on three-dimensional balanced steady-state free precession (bSSFP) and slab-selective inversion-recovery. Motion information was derived directly from the slab being imaged for online gating. Scan efficiency was maintained by an automatic adaptive online algorithm. Qualitative and quantitative assessments of image quality were performed and results were compared with conventional diaphragm navigator (NAV). RESULTS: NC MRA imaging was successfully completed in all subjects (n = 15). Similarly good image quality was observed in the proximal-middle renal arteries with ADIOS compared with NAV. Superior image quality was observed in the middle-distal renal arteries in the right kidneys with no NAV-induced artifacts. Maximal visible artery length was significantly longer with ADIOS versus NAV in the right kidneys. NAV setup was completely eliminated and scan time was significantly shorter with ADIOS on average compared with NAV. CONCLUSION: The proposed ADIOS technique for noncontrast MRA provides high-quality visualization of renal arteries with no diaphragm navigator-induced artifacts, simplified setup, and shorter scan time.
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Aumento da Imagem/métodos , Interpretação de Imagem Assistida por Computador/métodos , Angiografia por Ressonância Magnética/métodos , Reconhecimento Automatizado de Padrão/métodos , Artéria Renal/anatomia & histologia , Técnicas de Imagem de Sincronização Respiratória/métodos , Adulto , Algoritmos , Meios de Contraste , Retroalimentação , Humanos , Pessoa de Meia-Idade , Sistemas On-Line , Reprodutibilidade dos Testes , Mecânica Respiratória , Sensibilidade e Especificidade , Processamento de Sinais Assistido por Computador , Técnica de Subtração , Adulto JovemRESUMO
PURPOSE: To study temporal and spatial blurring artifacts from k-space view-sharing in time-resolved MR angiography (MRA) and to propose a technique for reducing these artifacts. METHODS: We acquired k-space data sets using a three-dimensional time-resolved MRA view-sharing sequence and retrospectively reformatted them into two reconstruction frameworks: full view-sharing via time-resolved imaging with stochastic trajectories (TWIST) and minimal k-space view-sharing and compressed sensing (CS-TWIST). The two imaging series differed in temporal footprint but not in temporal frame rate. The artifacts from view-sharing were compared qualitatively and quantitatively in nine patients in addition to a phantom experiment. RESULTS: CS-TWIST was able to reduce the imaging temporal footprint by two- to three-fold compared with TWIST, and the overall subjective image quality of CS-TWIST was higher than that for TWIST (P < 0.05). View sharing caused a delay in the visualization of small blood vessels, and the mean transit time of the carotid artery calculated based on TWIST reconstruction was 0.6 s longer than that for CS-TWIST (P < 0.01). In thoracic MRA, the shorter temporal footprint decreased the sensitivity to physiological motion blurring, and vessel sharpness was improved by 8.8% ± 6.0% using CS-TWIST (P < 0.05). CONCLUSION: In time-resolved MRA, the longer temporal footprint due to view-sharing causes spatial and temporal artifacts. CS-TWIST is a promising method for reducing these artifacts.
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Algoritmos , Artefatos , Compressão de Dados/métodos , Aumento da Imagem/métodos , Interpretação de Imagem Assistida por Computador/métodos , Angiografia por Ressonância Magnética/métodos , Humanos , Imageamento Tridimensional/métodos , Angiografia por Ressonância Magnética/instrumentação , Imagens de Fantasmas , Reprodutibilidade dos Testes , Sensibilidade e Especificidade , Análise Espaço-TemporalRESUMO
PURPOSE: Low pH is associated with intervertebral disc (IVD)-generated low back pain (LBP). The purpose of this work was to develop an in vivo pH level-dependent magnetic resonance imaging (MRI) method for detecting discogenic LBP, without using exogenous contrast agents. METHODS: The ratio of R1ρ dispersion and chemical exchange saturation transfer (CEST) (RROC) was used for pH-level dependent imaging of the IVD while eliminating the effect of labile proton concentration. The technique was validated by numerical simulations and studies on phantoms and ex vivo porcine spines. Four male (ages 42.8 ± 18.3) and two female patients (ages 55.5 ± 2.1) with LBP and scheduled for discography were examined with the method on a 3.0 Tesla MR scanner. RROC measurements were compared with discography outcomes using paired t-test. RESULTS: Simulation and phantom results indicated RROC is a concentration independent and pH level-dependent technique. Porcine spine study results found higher RROC value was related to lower pH level. Painful discs based on discography had significant higher RROC values than those with negative diagnosis (P < 0.05). CONCLUSION: RROC imaging is a promising pH level dependent MRI technique that has the potential to be a noninvasive imaging tool to detect painful IVDs in vivo.
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Algoritmos , Interpretação de Imagem Assistida por Computador/métodos , Degeneração do Disco Intervertebral/diagnóstico , Disco Intervertebral/química , Dor Lombar/diagnóstico , Imageamento por Ressonância Magnética/métodos , Animais , Biomarcadores/química , Concentração de Íons de Hidrogênio , Hidróxidos , Degeneração do Disco Intervertebral/complicações , Dor Lombar/etiologia , Imagens de Fantasmas , Reprodutibilidade dos Testes , Sensibilidade e Especificidade , SuínosRESUMO
PURPOSE: To propose a T1 mapping algorithm for the modified Look-Locker inversion-recovery (MOLLI) sequence that can improve T1 estimation accuracy. MATERIALS AND METHODS: The modified T1 mapping algorithm (InSiL) is based on the simulation of MOLLI signal evolution and simulates the longitudinal magnetization signal perturbation by each single-shot image acquisition in MOLLI as an instantaneous signal loss. InSiL was evaluated against original MOLLI using Bloch simulations, phantom studies, and in 15 healthy volunteers at 1.5T. RESULTS: In phantom studies, the maximum absolute error by InSiL is less than 2%, while that by MOLLI is more than 20% for T1 values from 221 msec to 1539 msec. The benefit of InSiL is greatest at heart rate (HR) >80 bpm and T1 >1000 msec, and InSiL reduced MOLLI T1 error from 14.9 ± 4.5% to 0.4 ± 0.3%. Average InSiL-derived native myocardial T1 values at 1.5T in healthy volunteers were significantly higher than MOLLI-derived values by 236.9 ± 11.7 msec (1160.3 ± 25.1 msec vs. 923.4 ± 22.3 msec, P < 0.001) at an average HR of 65.1 ± 14.7 bpm. CONCLUSION: The proposed InSiL approach yields better T1 mapping accuracy than MOLLI, and is less sensitive to HR variation in tissues with longer T1 values.
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Algoritmos , Coração/anatomia & histologia , Processamento de Imagem Assistida por Computador/métodos , Imageamento por Ressonância Magnética/métodos , Adulto , Feminino , Humanos , Masculino , Imagens de Fantasmas , Reprodutibilidade dos TestesRESUMO
PURPOSE: We propose a compressed-sensing (CS) technique based on magnitude image subtraction for high spatial and temporal resolution dynamic contrast-enhanced MR angiography (CE-MRA). METHODS: Our technique integrates the magnitude difference image into the CS reconstruction to promote subtraction sparsity. Fully sampled Cartesian 3D CE-MRA datasets from 6 volunteers were retrospectively under-sampled and three reconstruction strategies were evaluated: k-space subtraction CS, independent CS, and magnitude subtraction CS. The techniques were compared in image quality (vessel delineation, image artifacts, and noise) and image reconstruction error. Our CS technique was further tested on seven volunteers using a prospectively under-sampled CE-MRA sequence. RESULTS: Compared with k-space subtraction and independent CS, our magnitude subtraction CS provides significantly better vessel delineation and less noise at 4× acceleration, and significantly less reconstruction error at 4× and 8× (P < 0.05 for all). On a 1-4 point image quality scale in vessel delineation, our technique scored 3.8 ± 0.4 at 4×, 2.8 ± 0.4 at 8×, and 2.3 ± 0.6 at 12× acceleration. Using our CS sequence at 12× acceleration, we were able to acquire dynamic CE-MRA with higher spatial and temporal resolution than current clinical TWIST protocol while maintaining comparable image quality (2.8 ± 0.5 vs. 3.0 ± 0.4, P = NS). CONCLUSION: Our technique is promising for dynamic CE-MRA.
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Artérias/fisiologia , Compressão de Dados/métodos , Gadolínio , Interpretação de Imagem Assistida por Computador/métodos , Imageamento Tridimensional/métodos , Angiografia por Ressonância Magnética/métodos , Compostos Organometálicos , Técnica de Subtração , Algoritmos , Artérias/anatomia & histologia , Velocidade do Fluxo Sanguíneo/fisiologia , Meios de Contraste , Humanos , Aumento da Imagem/métodos , Reprodutibilidade dos Testes , Sensibilidade e EspecificidadeRESUMO
PURPOSE: To evaluate Off Resonance Insensitive Complementary SPAtial Modulation of Magnetization (ORI-CSPAMM) and Fourier Analysis of STimulated echoes (FAST) for the quantification of left ventricular (LV) systolic and diastolic function and compare it with the previously validated FAST+SPAMM technique. MATERIALS AND METHODS: LV short-axis tagged images were acquired with ORI-CSPAMM and SPAMM in healthy volunteers (n = 13). The FAST method was used to automatically estimate LV systolic and diastolic twist parameters from rotation of the stimulated echo and stimulated anti-echo about the middle of k-space subsequent to â¼3 min of user interaction. RESULTS: There was no significant difference between measures obtained for FAST+ORI-CSPAMM and FAST+SPAMM for mean peak twist (12.9 ± 3.4° versus 11.9 ± 4.0°; P = 0.4), torsion (3.3 ± 0.9°/cm versus 2.9 ± 1.0°/cm, P = 0.3), circumferential-longitudinal shear angle (9.1 ± 3.0° versus 8.2 ± 3.4°, P = 0.3), twisting rate (79.6 ± 20.2°/s versus 68.2 ± 23.4°/s, P = 0.1), untwisting rate (-117.5 ± 31.4°/s versus -106.6 ± 32.4°/s, P = 0.3), normalized untwisting rate (-9.3 ± 2.0/s versus -9.9 ± 4.4/s, P = 0.7), and time of peak twist (281 ± 18 ms versus 293 ± 25 ms, P = 0.04). FAST+ORI-CSPAMM also provided measures of duration of untwisting (148 ± 21 ms) and the ratio of rapid untwisting to peak twist (0.9 ± 0.3). Bland-Altman analysis of FAST+ORI-CSPAMM and FAST+SPAMM twist data demonstrates excellent agreement with a bias of -0.1° and 95% confidence intervals of (-1.0°, 3.2°). CONCLUSION: FAST+ORI-CSPAMM is a semi-automated method that provides a quick and quantitative assessment of LV systolic and diastolic twist and torsion. ORI-CSPAMM corrects off-resonance accrued during tagging preparation and readout and visibly removes chemical shift from the tagging pattern, which confers greater robustness to the derived quantitative measures.
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Técnicas de Imagem de Sincronização Cardíaca/métodos , Interpretação de Imagem Assistida por Computador/métodos , Imageamento Tridimensional/métodos , Imagem Cinética por Ressonância Magnética/métodos , Contração Miocárdica/fisiologia , Função Ventricular Esquerda/fisiologia , Adulto , Algoritmos , Diástole , Feminino , Ventrículos do Coração/anatomia & histologia , Humanos , Aumento da Imagem/métodos , Masculino , Reprodutibilidade dos Testes , Rotação , Sensibilidade e Especificidade , SístoleRESUMO
The reduced field-of-view (rFOV) turbo-spin-echo (TSE) technique, which effectively suppresses bowel movement artifacts, is developed for the purpose of chemical exchange saturation transfer (CEST) imaging of the intervertebral disc (IVD) in vivo. Attempts to quantify IVD CEST signals in a clinical setting require high reliability and accuracy, which is often compromised in the conventionally used technique. The proposed rFOV TSE CEST method demonstrated significantly superior reproducibility when compared with the conventional technique on healthy volunteers, implying it is a more reliable measurement. Phantom study revealed a linear relation between CEST signal and glycosaminoglycan (GAG) concentration. The feasibility of detecting IVD degeneration was demonstrated on a healthy volunteer, indicating that the proposed method is a promising tool to quantify disc degeneration.
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Disco Intervertebral/patologia , Vértebras Lombares/patologia , Imageamento por Ressonância Magnética , Marcadores de Spin , Adulto , Feminino , Glicosaminoglicanos/metabolismo , Voluntários Saudáveis , Humanos , Degeneração do Disco Intervertebral/patologia , Masculino , Imagens de FantasmasRESUMO
Fluid attenuated inversion recovery (FLAIR) MRI sequences have become an indispensible tool for defining the malignant boundary in patients with brain tumors by nulling the signal contribution from cerebrospinal fluid allowing both regions of edema and regions of non-enhancing, infiltrating tumor to become hyperintense on resulting images. In the current study we examined the utility of a three-dimensional double inversion recovery (DIR) sequence that additionally nulls the MR signal associated with white matter, implemented either pre-contrast or post-contrast, in order to determine whether this sequence allows for better differentiation between tumor and normal brain tissue. T1- and T2-weighted, FLAIR, dynamic susceptibility contrast (DSC)-MRI estimates of cerebral blood volume (rCBV), contrast-enhanced T1-weighted images (T1+C), and DIR data (pre- or post-contrast) were acquired in 22 patients with glioblastoma. Contrast-to-noise (CNR) and tumor volumes were compared between DIR and FLAIR sequences. Line profiles across regions of tumor were generated to evaluate similarities between image contrasts. Additionally, voxel-wise associations between DIR and other sequences were examined. Results suggested post-contrast DIR images were hyperintense (bright) in regions spatially similar those having FLAIR hyperintensity and hypointense (dark) in regions with contrast-enhancement or elevated rCBV due to the high sensitivity of 3D turbo spin echo sequences to susceptibility differences between different tissues. DIR tumor volumes were statistically smaller than tumor volumes as defined by FLAIR (Paired t test, P = 0.0084), averaging a difference of approximately 14 mL or 24 %. DIR images had approximately 1.5× higher lesion CNR compared with FLAIR images (Paired t test, P = 0.0048). Line profiles across tumor regions and scatter plots of voxel-wise coherence between different contrasts confirmed a positive correlation between DIR and FLAIR signal intensity and a negative correlation between DIR and both post-contrast T1-weighted image signal intensity and rCBV. Additional discrepancies between FLAIR and DIR abnormal regions were also observed, together suggesting DIR may provide additional information beyond that of FLAIR.
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Neoplasias Encefálicas/patologia , Meios de Contraste , Glioblastoma/patologia , Imageamento Tridimensional , Imageamento por Ressonância Magnética , Recidiva Local de Neoplasia/patologia , Progressão da Doença , Humanos , Aumento da Imagem , Processamento de Imagem Assistida por Computador , PrognósticoRESUMO
High doses of radiation to the hippocampus have been correlated with increased cognitive decline following radiation therapy for brain metastases. To mitigate these effects, a variety of hippocampal sparing techniques have been implemented for both whole brain radiation therapy (WBRT) and stereotactic radiosurgery (SRS). The goal of this review article is to provide a practical resource for the clinical implementation of hippocampal-sparing radiation therapy, starting with a brief background on the function and delineation of the hippocampal structure, as well as radiation effects on the hippocampus and the most widely recommended dose constraints. Considerations for treatment simulation are discussed, including options for cranial immobilization and optional head tilt. Hippocampal sparing has been demonstrated for WBRT using helical TomoTherapy, static intensity-modulated radiation therapy (IMRT), and volumetric-modulated arc therapy (VMAT) with a variety of patient setup positions, beam arrangements, and planning parameters. Tomotherapy has been shown to achieve slightly greater hippocampal sparing in some studies, while VMAT enables the most efficient treatment delivery. Hippocampal sparing has also been evaluated in a wide range of studies for both GammaKnife and linear accelerator (LINAC)-based SRS, with the proximity of metastases to the hippocampus being the most significant predictor of hippocampal dose. The methods and resulting hippocampal doses from these studies on both WBRT and SRS are discussed, as well as the role of automation in hippocampal sparing radiation therapy.
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Neoplasias Encefálicas , Radiocirurgia , Radioterapia de Intensidade Modulada , Humanos , Planejamento da Radioterapia Assistida por Computador/métodos , Dosagem Radioterapêutica , Irradiação Craniana/métodos , Neoplasias Encefálicas/radioterapia , Neoplasias Encefálicas/secundário , Radioterapia de Intensidade Modulada/métodos , Hipocampo/efeitos da radiaçãoRESUMO
Historically, patient datasets have been used to develop and validate various reconstruction algorithms for PET/MRI and PET/CT. To enable such algorithm development, without the need for acquiring hundreds of patient exams, in this article we demonstrate a deep learning technique to generate synthetic but realistic whole-body PET sinograms from abundantly available whole-body MRI. Specifically, we use a dataset of 56 18F-FDG-PET/MRI exams to train a 3-D residual UNet to predict physiologic PET uptake from whole-body T1-weighted MRI. In training, we implemented a balanced loss function to generate realistic uptake across a large dynamic range and computed losses along tomographic lines of response to mimic the PET acquisition. The predicted PET images are forward projected to produce synthetic PET (sPET) time-of-flight (ToF) sinograms that can be used with vendor-provided PET reconstruction algorithms, including using CT-based attenuation correction (CTAC) and MR-based attenuation correction (MRAC). The resulting synthetic data recapitulates physiologic 18F-FDG uptake, e.g., high uptake localized to the brain and bladder, as well as uptake in liver, kidneys, heart, and muscle. To simulate abnormalities with high uptake, we also insert synthetic lesions. We demonstrate that this sPET data can be used interchangeably with real PET data for the PET quantification task of comparing CTAC and MRAC methods, achieving ≤ 7.6% error in mean-SUV compared to using real data. These results together show that the proposed sPET data pipeline can be reasonably used for development, evaluation, and validation of PET/MRI reconstruction methods.
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PURPOSE: To validate a novel method for the rapid and facile quantification of left ventricular (LV) twist from tagged magnetic resonance images and demonstrate the potential clinical utility in a series of 20 healthy volunteers. MATERIALS AND METHODS: Cardiac magnetic resonance imaging (MRI) short-axis images were acquired with tissue tagging in 20 healthy subjects and six canines. The tagged images were processed using a novel Fourier Analysis of the STimulated echoes (FAST) method, which uses a series of Fourier-space operations to measure LV twist with limited user interaction. A subset of eight healthy subjects and the canine data were compared to results from previously validated "gold standard" software (FindTags). Interobserver and intraobserver coefficients of variation (CV(INTER) and CV(INTRA) ), linear regression, and Bland-Altman analyses were used to assess agreement between observers and methods. RESULTS: CV(INTRA) for peak systolic twist (2.9% and 2.6%) and CV(INTER) (4.3% and 4.2%) were all small. Linear regression analysis of the FAST and FindTags twist values indicated very good agreement in healthy subjects (R = 0.91) and in canines (R = 0.95). Bland-Altman comparison of the FAST and FindTags twist results indicated excellent agreement in healthy subjects (bias of -0.5°, 95% confidence intervals (-4.3°, 4.3°)) and canines (bias of 0.2°, 95% confidence intervals (-2.7°, 3.1°)). Peak systolic twist in healthy subjects averaged 10.5 ± 1.9° degrees. CONCLUSION: The FAST method for quantifying LV twist produces results that are not significantly different from the current "gold standard" in a fraction of the user interaction time and has demonstrated feasibility in human subjects.
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Ventrículos do Coração/anatomia & histologia , Imagem Cinética por Ressonância Magnética/métodos , Sístole/fisiologia , Função Ventricular Esquerda/fisiologia , Adulto , Animais , Técnicas de Imagem de Sincronização Cardíaca/métodos , Cães , Feminino , Análise de Fourier , Humanos , Modelos Lineares , Masculino , Contração Miocárdica/fisiologiaRESUMO
OBJECTIVE: Simultaneous PET/MRIs vary in their quantitative PET performance due to inherent differences in the physical systems and differences in the image reconstruction implementation. This variability in quantitative accuracy confounds the ability to meaningfully combine and compare data across scanners. In this work, we define image reconstruction parameters that lead to comparable contrast recovery curves across simultaneous PET/MRI systems. METHOD: The NEMA NU-2 image quality phantom was imaged on one GE Signa and on one Siemens mMR PET/MRI scanner. The phantom was imaged at 9.7:1 contrast with standard spheres (diameter 10, 13, 17, 22, 28, 37 mm) and with custom spheres (diameter: 8.5, 11.5, 15, 25, 32.5, 44 mm) using a standardized methodology. Analysis was performed on a 30 min listmode data acquisition and on 6 realizations of 5 min from the listmode data. Images were reconstructed with the manufacturer provided iterative image reconstruction algorithms with and without point spread function (PSF) modeling. For both scanners, a post-reconstruction Gaussian filter of 3-7 mm in steps of 1 mm was applied. Attenuation correction was provided from a scaled computed tomography (CT) image of the phantom registered to the MR-based attenuation images and verified to align on the non-attenuation corrected PET images. For each of these image reconstruction parameter sets, contrast recovery coefficients (CRCs) were determined for the SUVmean, SUVmax and SUVpeak for each sphere. A hybrid metric combining the root-mean-squared discrepancy (RMSD) and the absolute CRC values was used to simultaneously optimize for best match in CRC between the two scanners while simultaneously weighting toward higher resolution reconstructions. The image reconstruction parameter set was identified as the best candidate reconstruction for each vendor for harmonized PET image reconstruction. RESULTS: The range of clinically relevant image reconstruction parameters demonstrated widely different quantitative performance across cameras. The best match of CRC curves was obtained at the lowest RMSD values with: for CRCmean, 2 iterations-7 mm filter on the GE Signa and 4 iterations-6 mm filter on the Siemens mMR, for CRCmax, 4 iterations-6 mm filter on the GE Signa, 4 iterations-5 mm filter on the Siemens mMR and for CRCpeak, 4 iterations-7 mm filter with PSF on the GE Signa and 4 iterations-7 mm filter on the Siemens mMR. Over all reconstructions, the RMSD between CRCs was 1.8%, 3.6% and 2.9% for CRC mean, max and peak, respectively. The solution of 2 iterations-3 mm on the GE Signa and 4 iterations-3 mm on Siemens mMR, both with PSF, led to simultaneous harmonization and with high CRC and low RMSD for CRC mean, max and peak with RMSD values of 2.8%, 5.8% and 3.2%, respectively. CONCLUSIONS: For two commercially available PET/MRI scanners, user-selectable parameters that control iterative updates, image smoothing and PSF modeling provide a range of contrast recovery curves that allow harmonization in harmonization strategies of optimal match in CRC or high CRC values. This work demonstrates that nearly identical CRC curves can be obtained on different commercially available scanners by selecting appropriate image reconstruction parameters.
RESUMO
Purpose: One major challenge facing simultaneous positron emission tomography (PET)/ magnetic resonance imaging (MRI) is PET attenuation correction (AC) measurement and evaluation of its accuracy. There is a crucial need for the evaluation of current and emergent PET AC methodologies in terms of absolute quantitative accuracy in the reconstructed PET images. Approach: To address this need, we developed and evaluated a lesion insertion tool for PET/MRI that will facilitate this evaluation process. This tool was developed for the Biograph mMR and evaluated using phantom and patient data. Contrast recovery coefficients (CRC) from the NEMA IEC phantom of synthesized lesions were compared to measurements. In addition, SUV biases of lesions inserted in human brain and pelvis images were assessed from PET images reconstructed with MRI-based AC (MRAC) and CT-based AC (CTAC). Results: For cross-comparison PET/MRI scanners AC evaluation, we demonstrated that the developed lesion insertion tool can be harmonized with the GE-SIGNA lesion insertion tool. About < 3 % CRC curves difference between simulation and measurement was achieved. An average of 1.6% between harmonized simulated CRC curves obtained with mMR and SIGNA lesion insertion tools was achieved. A range of - 5 % to 12% MRAC to CTAC SUV bias was respectively achieved in the vicinity and inside bone tissues in patient images in two anatomical regions, the brain, and pelvis. Conclusions: A lesion insertion tool was developed for the Biograph mMR PET/MRI scanner and harmonized with the SIGNA PET/MRI lesion insertion tool. These tools will allow for an accurate evaluation of different PET/MRI AC approaches and permit exploration of subtle attenuation correction differences across systems.
RESUMO
Long-term methamphetamine (MA) abuse is associated with a wide range of deficits on explicit tasks of selective attention. Less is known however about the effects of MA abuse on implicit measures of attention. Accordingly, we used a computerized spatial priming task to assess implicit attentional processes in 54 MA dependent subjects (mean age=37.04+/-8.9 years) and 32 healthy controls without history of any form of substance abuse (mean age=33.63+/-7.05 years). The MA dependent subjects had been drug-abstinent a minimum of 3 weeks with a mean duration of MA use of 13.27+/-7.75 years. The MA dependent subjects did not differ significantly from controls on either inhibitory priming [p=.37] or facilitory priming) [p=.69]. This result comports with our earlier findings of intact object-based priming in MA dependent individuals and suggests that intact priming effects extend across spatial domains. Further, this pattern of sparing suggests that cortical brain systems typically supporting implicit attentional functioning are relatively intact in long-term MA dependent individuals whereas brain systems supporting explicit attentional processes are affected.
Assuntos
Atenção/fisiologia , Metanfetamina/efeitos adversos , Transtornos Relacionados ao Uso de Substâncias/fisiopatologia , Adulto , Feminino , Humanos , Inibição Psicológica , Masculino , Pessoa de Meia-Idade , Testes Neuropsicológicos , Reconhecimento Visual de Modelos , Estimulação Luminosa/métodos , Tempo de Reação/fisiologia , Percepção Espacial/fisiologiaRESUMO
The goal of this study was to examine behavioral characteristics of currently drug-abstinent methamphetamine (MA)-dependent subjects (n=39) who experienced psychotic symptoms associated with MA abuse. All participants completed the Wender Utah Rating Scale (WURS), which retrospectively assesses Attention Deficit Hyperactivity Disorder-relevant childhood behaviors. The results suggest the existence of possible behavioral markers reflecting an early cognitive vulnerability to the development of frequent MA-induced psychotic symptoms as well as increased vulnerability associated with a family history of psychiatric illness.