Extremities CBCT 7/14/2015 Advances in Cone-Beam CT and Emerging Applications
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7/14/2015 Advances in Cone-Beam CT and Emerging Applications: Extremities CBCT W Zbijewski Department of Biomedical Engineering Johns Hopkins University The I-STAR Laboratory istar.jhu.edu Imaging for Surgery, Therapy, and Radiology JH Siewerdsen, JW Stayman, A Sisniega, G Gang, Q Cao, A Muhit, P DeJean, P Prakash Carestream Health J Yorkston, N Packard, R Senn, D Yang JHU Radiology JA Carrino, G Thawait, S Demehri, M Mahesh, A. Machado Funding Support Carestream Health NIH 2R01-CA-112163 NIH R21-AR-062293 NIH R01-EB-0188961 Clinical Motivation Insufficiency fractures Osteoporosis Dietary deficiencies Radiation therapy →Need for biomarkers 50 JHU Radiology →Monitoring of healing JHU Radiology Fracture / Trauma 100 150 200 250 300 350 Arthritis 400 Osteoarthritis (OA) ~30 million US adults Joint replacement →Need for early biomarkers 450 Rheumatoid arthritis ~1.5 million US adults Deformity and chronic pain Novel drugs →Monitoring of treatment response Gout ~8 million US adults →DE imaging 500 50 100 150 200 250 300 350 400 450 Imaging capabilities: • Contrast resolution Joint space, tendons, ligaments • Spatial resolution Bone micoarchitecure • Bone composition (quantitative) • Weight-bearing (functional) • Longitudinal studies 1 7/14/2015 MSK Radiology Contrast resolution Spatial resolution Quantitative + +++ ++ +++ + + ++ + ++ +++ ++(+) ++ +++ + Rad First line imaging Fluoro Motion Functional Functional (load-bearing) (motion) CT Trauma Fracture MRI +++ Joint internal derangement US + ++ + ++ +++ + ++ ++ + +++ ++ CT (www.GE.com) ++ MRI (www.GE.com) Soft-tissue lesions Guidance NM Infection +++ CT – high-resolution bone – limited + soft tissue + MR – exquisite soft tissue MR – limited spatial resolution (Dual Energy-CT) A Dedicated Extremity CBCT Scanner System Configuration Flat-panel detector (FPD) Compact gantry Sitting / standing examination Carestream + JHU* Capabilities Weight-bearing scans Natural stance High isotropic spatial resolution Multi-mode Rad / Fluoro / CBCT Simplified logistics Modest imaging dose Longitudinal studies Planmed Verity** *Zbijewski et al. Med Phys 2011 et al. Radiology 2014 et al. AJR 2013 et al. Skeletal Radiol 2015 *Carrino **Tuominen ** Huang planmed.com Scanner Configuration Standing Configuration General considerations Side entry – sliding door Natural stance FOV: 20 x 20 x 20 cm 3 ~20 sec/scan X-ray source and FPD Fixed anode, 0.5 focal spot 50-125 kVp, 0.8 kW max 0.194 mm detector pixel Clinical Prototype Patient studies: Weight-bearing lower extremities Arthritis and trauma Sitting Configuration FPD X-ray Tube Application Development Joint space morphology Bone health Bone microarchitecture Bone Mineral Density (BMD) Side Entry 2 7/14/2015 Spatial Resolution Line-Pair Pattern High-Res Nominal 21 21 Nominal Protocol (2x2 Binning) 0.388 mm pixels (0.26 mm voxels) 20 20 High-Res Protocol (1x1 Binning) 0.194 mm pixels (0.13 mm voxels) 19 19 1 18 0.9 0.8 17 18 lp/cm 17 lp/cm 0.7 1x1 (Ramp) |MTF| 0.6 0.5 16 16 15 15 1x1 (Hann) 0.4 14 14 0.3 2x2 2x2 (Ramp) (Hann) 0.2 0.1 0 0.5 1 Cadaver Hand 1.5 2 2.5 3 Frequency [lp/mm] Contrast Resolution Constant dose ~10 mGy 60 kVp Max Power ~0.875 kW 5.7 mGy 3 Adipose (-100 HU) 2.5 3 mGy 80 kVp SDNR 2 BR-1 (-45 HU) 1.5 1 100 kVp 0.5 Muscle (+10 HU) 0 60 70 80 90 100 110 120 kVp Dynamic Gain, 2X2 Binning (0.388 mm pixels) 0.52 mm isotropic voxels, Hann Filter Cadaver knee Diagnostic Imaging Performance CBCT (10 mGy) MDCT (25 mGy) CBCT – MDCT comparison Bone and soft-tissue visualization tasks CBCT: 1st generation prototype MDCT: Siemens Definition Bone Recon Ramp Filter 0.26 mm voxels isotropic Bone Recon ‘Ultra-High-Res’ 0.4 mm voxels isotropic Observer study Fresh cadavers 10x knee, 10x hand 4 expert radiologists 8 diagnostic tasks Preference and satisfaction Soft Tissues Soft Tissues Hann Fitler ‘UHR Soft’ Protocol 0.52 mm voxels isotropic 0.6 mm voxels isotropic Demehri et al, Eur Radiol 2015 3 7/14/2015 Diagnostic Imaging Performance CBCT (10 mGy) Knee MDCT (25 mGy) Bone Tasks Tissue* Excellent 5 4Cortical Bone Medullary 2Bone Poor 1Fracture (if ppresent) = 0.026 Fair 3 Bone Recon Ramp Filter 0.26 mm voxels isotropic Bone Recon ‘Ultra-High-Res’ 0.4 mm voxels isotropic CBCT Hand Bone Tasks * * Criteria * Assessment 5 Visibility4 and integrity 3 Architecture of trabeculae 2 Detection 1 and characterization p = 0.353 MDCT CBCT MDCT Soft Tissue Tasks Hand Soft Tissue Tasks Assessment Criteria 5 density * Uniform * Integrity at attachment 4 * * Distinguish superficial from deep 3 Muscle Architecture of muscle 2 of ligaments Ligaments Integrity Fat Uniformity visibilityand 1 and Observer study CBCT vs. MDCT p < 0.001 p < width 0.001 Articular space radiographyJoint for fractures: Huang at el, Cartilage CBCT Rad MDCT CBCT Skel 2015 (Planmed Verity)MDCT Knee Tissue Excellent 5 Tendon 4 Fair 3 2 Soft Tissues Soft Tissues Hann Fitler ‘UHR Soft’ Protocol 0.52 mm voxels isotropic 0.6 mm voxels isotropic Poor 1 Bone Imaging: Fracture Healing Week 9 Week 15 Joint space width (JSW) Bone image Medial femoral condyle to tibial plateau Joint Space Width (JSW) (mm) Joint Space Analysis in OA p < 0.001 Meniscal Soft-tissue image protrusion (MP) 3.3 4.65 mm 3.21 OA: 2.05 OA: 1.45 17 patients with OA of the knee OA 18 patients without OA Normal 3 observers Non-Weight Bearing Weight-bearing (WB) vs. Non-weight bearing (NWB): (NWB) Significant difference in JSW for OA Normal OA Weight Bearing (WB) JSW change in OA Study setup Thawait et al. RSNA 2013 4 7/14/2015 Joint Space Analysis in OA p = 0.001 Meniscal Extrusion (ME) (mm) Meniscal Extrusion (ME) Soft-tissue image 4.65 mm 7.8 6.81 2.42 2.59 Study setup 17 patients with OA of the knee OA 18 patients without OA Normal 3 observers Non-Weight Bearing Weight-bearing (WB) vs. Non-weight bearing (NWB): (NWB) Significant difference in JSW for OA Significant difference in ME for OA No significant difference in JSW or ME for non-OA Normal OA Weight Bearing (WB) WB vs. NWB hindfoot alignement: Hirschmann at el, Eur Rad 2014 (Planmed Verity) The Electrostatic Model π½ ππ π = ππ π¬ = −ππ½ π π⋅π¬=π π ⊂ βπ , βπ ⇒ ππ π½ π = π ∀π ∈ π π π½ – Electric potential [V] π – Charge density [πΆ ⋅ π −3] π – Joint space of interest π½ ππ π = ππ For an electric field πΈcharacterized by field lines l (ππ × πΈ = 0) π½ππ π₯0 , π¦0 , π§0 = π 1 π 0 ππ π ππ πππ πππ π₯0 , π¦0 , π§0 ∈ π0 Ω Cao et al Phys Med Biol 2015 Joint Space Maps Normal A015 A066 Classification Accuracy A072 Electrostatic Model JSM A067 A041 A073 Minimum JSW Osteoarthritic M A021 A A030 A038 A031 A043 Radiologist L P A023 5 7/14/2015 Quantitative Imaging of Bone Health 50 Micro-CT 100 Bone health qCT 150 Structure: Micro-architecture (micro-CT) Composition: Bone Mineral Density BMD (DEXA / qCT) Bone Marrow Edema BME (T2-weighted MRI) (increased fluid content) Risk of fracture Mechanical competency (e.g. response to load) Osteoporosis, arthritis, insufficiency fractures 200 250 300 350 www.qct.com 400 450 500 50 100 150 200 250 300 350 400 450 T2 MRI CBCT: integrated platform for bone health assessment Superior bone visualization to conventional CT BME Micro-architecture: High resolution required (~100 mm) →Model-based reconstruction with deblurring →Multi-resolution model-based reconstruction (speed) →CMOS detectors *Sisniega et al, Phys. Med. Biol. (2015) Quantitative Imaging: Microarchitecture Trabecular Thickness (mm) 50 1.2 200 Micro CT (mCT) 250 300 (Johns Hopkins Univ) 40 % 0.5 350 Ex Vivo avox = 0.1 mm 400 450 500 50 100 150 200 250 300 350 400 450 0.0 MDCT (Siemens Somatom) Structure Model Index In Situ avox = 0.36 mm MDCT mCT MDCT (In Situ) MCCT (Ex Vivo) CBCT In Situ avox = 0.1 mm CBCT (In Situ) 0 MDCT mCT MDCT (In Situ) CBCT MCCT (Ex Vivo) CBCT (In Situ) 1.0 4.5 % Muhit et al. SPIE 2013 2% 0.2 CBCT 5 3% 2.5 (Dedicated Prototype) 140 % 0.7 1% MDCT mCT MDCT (In Situ) Degree of Anisotropy 150 Trabecular Volume Fraction 1.0 100 MCCT (Ex Vivo) 42 % 0.5 0.0 CBCT CBCT (In Situ) 50 % MDCT mCT MDCT (In Situ) MCCT (Ex Vivo) CBCT CBCT (In Situ) Ultra-High-Resolution CBCT Imaging : Deblurring and Noise Correlations in PWLS Source Blur ππ Bs Extended X-ray Source Bd Detector Blur ππ X-ray Photons Light Photons Object Photodiodes Scintillator Uncorrelated Uncorrelated, Attenuated Correlated Light Photons Correlated Electrons with Light Spread with Readout Noise Bare Beam X-rays with Focal Spot Blur Penalized Weighted Least Squares with Deblurring and Noise Covariance: System Matrix Roughness Penalty Image Estimate π = arg π min[ Aπ − π π πΎπΏ−1 π΄π − π + π½π π ] Covariance Matrix: Accounts for blur and deblurring Deblurred line integrals Tilley et al, Fully 3D Mtg 2015 6 7/14/2015 Deblurring and Noise Correlations in PWLS Experimental setup dominated by source blur Deblurring the source blur introduces correlations Modelling the correlations reduces noise in deblurred PWLS Both with Deblur Ultra-High-Resolution CBCT Imaging : Multi-Resolution Model-Based Reconstruction System Matrix Image Estimate π = arg π min[ Aπ − π π πΎπΏ−1 π΄π − π + π½π π ] Challenges for High Resolution PWLS System matrix A is large Multi-resolution PWLS System matrix separates into: -standard resolution component ASTD -fine resolution component AFINE π¦ = πΌ0 exp −π΄π = πΌ0 exp π¨πΊπ»π«π« π ππΊ βexp(π¨ππ°π΅πππ ) Cao et al, Fully 3D Mtg 2015 Multi-Resolution Reconstruction No Downsampling Downsampling=4 Downsampling=10 Fine Grid RMSE Downsampling=10 No Downsampling Digital Phantom Study Fixed regularization in m F Varied regularization and downsampling in m S No visible artifacts in m F for downsampling ≤ 4 10x – 100x acceleration while maintaining quality in mF 7 7/14/2015 Multi-Resolution Reconstruction Knee phantom on a CBCT test-bench in extremities CBCT configuration Ultra-High-Resolution CBCT Imaging : CMOS detectors Flat Panel Varian 4030 0.194 mm pixels CMOS vs. aSi Flat Panel Higher resolution (smaller pixels) Lower electronic noise ~500 electrons/pixel Faster read-out 30 fr/sec for 30x30 cm FOV CMOS Dalsa Xineos 3030 0.1 mm pixels PSF of a 0.15 mm steel wire CMOS Experimental evaluation 600 mm CsI for CMOS and Flat Panel Extremities CBCT configuration 0.4 focal spot x-ray tube 75 mm voxels, Ramp filter Flat Panel FWHM ~0.26 mm Results and Future Work ~10-15% improvement in PSF FWHM ~0.31 mm [mm] Ultra-High-Resolution CBCT Imaging : CMOS detectors CMOS vs. aSi Flat Panel Higher resolution (smaller pixels) Lower electronic noise ~500 electrons/pixel Faster read-out 30 fr/sec for 30x30 cm FOV CMOS Dalsa Xineos 0.1 mm pixels Experimental evaluation 600 mm CsI for CMOS and Flat Panel Extremities CBCT configuration 0.4 focal spot x-ray tube 75 mm voxels, Ramp filter Flat Panel Varian 4030 0.194 mm pixels Results and Future Work ~10-20% improvement in PSF Better delineation of trabecular detail CMOS limited by thick scintillator Analytical optimization of scintillator thickness Task-based Detectability d’ 8 7/14/2015 Quantitative Imaging of Bone Health 50 Micro-CT 100 Bone health qCT 150 Structure: Micro-architecture (micro-CT) Composition: Bone Mineral Density BMD (DEXA / qCT) Bone Marrow Edema BME (T2-weighted MRI) (increased fluid content) Risk of fracture Mechanical competency (e.g. response to load) Osteoporosis, arthritis, insufficiency fractures 200 250 300 350 www.qct.com 400 450 500 50 100 150 200 250 300 350 400 450 T2 MRI CBCT: integrated platform for bone health assessment Bone Mineral Density / Bone Marrow Edema Accurate attenuation values →Comprehensive artifact correction * BME challenging in conventional CT (partial volume from trabeculae) Material decomposition →Dual Energy (DE) imaging BME *Sisniega et al, Phys. Med. Biol. (2015) Quantitative Imaging: BMD BMD calculated using CBCT and MDCT (Mindways QCT) BMD standard materials (CaHA rods) embedded in scanner door CBCT with scatter correction BMD calibration: 0, 75, and 150 mg/mL CaHA rods BMD (mg/mL) Osteoporotic (75 mg/mL) Healthy (150 mg/mL) 85 160 2.1% 0.3% 75 150 1.1% 3.1% 65 1 CBCT 140 2 MDCT 2 MDCT 1 CBCT BMD Test Phantom: 16 cm polyethylene cylinder CaHA inserts: 0, 75, 125, 150, 250 mg/mL Muhit et al. SPIE 2013 Dual Energy Imaging of Bone Health ππ―π¬ ππ³π¬ 1/mm 0.03 Image-based DE Three-material decomposition Volume preservation constraint Volume fractions of: Water + Fat/Marrow + Cortical Bone Requires good image uniformity 0.018 Water Fraction Marrow Fraction Bone Fraction DE Measurement of BMD Bone fraction → BMD DE Imaging of BME DE: Increased water fraction=edema * 0.3 1 Vol. Frac. *Pache 0.3 1 Vol. Frac. 0 0.12 Vol. Frac. et al, Radiology (2010) 9 7/14/2015 DE CBCT: Experimental Study Volume Composition Edema Inserts Base Materials Tissue-Mimicking Materials* Cortical Bone=Dipotassium Phosphate K2HPO4 Marrow/Fat=Ethanol Edema: Decreasing fraction of ethanol Imaging Experiments ~10 cm diameter phantom HE: 105 kVp, 0.1 mAs/frame, ~7 mGy CTDI LE: 60 kVp, 0.8 mAs/frame, ~7 mGy CTDI Water 100% H2O Marrow 100% C2H6O Cortical Bone 100% K2HPO4 Bone75 75 mg/ml K2HPO4 in H2O Bone100 100 mg/ml K2HPO4 in H20 Marrow Bone100 10% 10% 90% 25% 25% 75% 40% 40% 60% Fast GPU Monte Carlo scatter ~5 min correction per scan 1/mm 25% 10% Artifact Correction correction ** 0.026 Bone100 Marrow 40% 0.02 Bone75 *Goodsitt **Sisniega et al, Investig. Radiol (1987) et al, Phys. Med. Biol. (2015) Three-Material DE Decomposition Water Marrow Bone Narrow Beam “in-air” 10% Narrow Beam Water 25% Marrow Bone Marrow 40% Bone75 Full Beam Scatter Correction 0.02 0.026 0.75 1/mm 0.04 1 0 0.25 0.05 BMD Accuracy with Dual Energy CBCT DE estimates of bone and marrow volume fractions Relative difference with “in-air” narrow beam DE 25% Rel. diff.=0.03 10% Rel. diff. =0.01 “in-air” Bone100 Rel. diff. =0.01 40% Marrow Bone75 25% Bone100 40% Rel. diff.=0.01 10% 40% Marrow Bone75 25% 10% Measured Cortical Bone Vol. Fraction “in-air” Bone100 Marrow Vol. Fraction Measured Bone75 Rel. diff.=0.09 0 0.05 Bone vol. frac. 10 7/14/2015 Dual Energy with Three Source CBCT 3 source 1 source HEsup LEcentral HEinf Three-Source CBCT Configuration Custom fixed-anode unit Three x-ray tubes arranged axially Increased Field-of-View Reduced cone beam artifacts New method for Dual-Energy CBCT Obviates need for double scan Image Reconstruction in 3-Source DE CBCT LEcentral Penalized Likelihood (PL) mˆ ο½ arg max m L ο¨ m; y ο© ο ο’ R ο¨ m ο© * Forward model L(µ; y) Edge-preserving Huber penalty R central slice 1/mm 0.03 0.018 Low Energy reconstruction Combined PL reconstruction L(µ; y) involves LEcentral projections HEsup * High Energy reconstruction L(µ; y) combines HEsup and HEinf HE3 reconstruction HE1 reconstruction HEinf * Bone and Fat Fractions in Cadaveric Knee LE: 60 kVp, 7 mGy HE: 105 kVp, 7 mGy PL reconstruction Narrow Beam Double Scan DE Narrow Beam 105 kVp Double Scan DE Marrow frac.=0.74±0.13 Bone frac.=0.059±0.008 Marrow frac.=0.65±0.16 Bone frac.=0.034±0.004 0.016 0.024 1/mm 0.1 1 Fat vol. frac. Three-Source DE Marrow frac.=0.88±0.08 Bone frac.=0.064±0.005 Marrow frac.=0.48±0.18 Bone frac.=0.027±0.006 0.12 0 Bone vol. frac. 11 7/14/2015 Bone and Fat Fractions in Cadaveric Knee LE: 60 kVp, 7 mGy HE: 105 kVp, 7 mGy PL reconstruction Double Scan DE Three-Source DE Marrow frac.=0.95±0.03 Bone frac. =0.032±0.005 1/mm 0.016 0.02 0.024 Marrow frac.=0.85±0.09 Bone frac.=0.029±0.006 Fat vol. frac. 0.1 0.55 1 0 0.6 0.12 Bone vol. frac. Conclusions Extremities CBCT Weight bearing Soft tissue contrast Isotropic spatial resolution (~0.5 mm) Low dose (~10 mGy) (~20-40 mGy for high-resolution MDCT) Novel applications 3D Joint space maps Quantitative imaging of bone health Ultra-high resolution CBCT for bone morphometry Advanced blur and noise models in PWLS Multi-resolution PWLS Improved delineation of trabeculae with CMOS Scintillator optimization Motion correction Quantitative CBCT of bone composition Peripheral qCT DE imaging BMD accuracy within 15% of “in-air” value Detection of edema in DE CBCT Marrow volume fraction changes ≥ 20% 12
