Pre-clinical Imaging Roger Lecomte, Ph.D. Lecture 1: Thursday July 26, 2018, 9:15 Department of Nuclear R. Lecomte − Ohrid 2018 Workshop − July 25-28, 2018 Medicine & Radiobiology 1 Duality of Interest Statement IR&T Inc. – Co-founder & CSO Research contracts: Charles River, Bayer, Biogen R. Lecomte − Ohrid 2018 Workshop − July 25-28, 2018 2 Outline • Preclinical Imaging − Morphological/anatomical − Molecular imaging • Modalities − Overview (US, MRI, optical) − µCT − µSPECT − µPET • Applications − Multimodality imaging R. Lecomte − Ohrid 2018 Workshop − July 25-28, 2018 3 Why Small Animal Imaging ? • The rat and mouse host a large number of human diseases ∗ Opportunity to study disease progression / therapeutic response under controlled conditions non-invasively in same animal repetitively • Powerful tool for research into molecular pathways and biomarker identification ∗ Molecular targets, receptors & drug binding sites ∗ Relationship between genes ↔ phenotype ∗ Gene expression & gene therapy assessment • Bridge between in vitro / in vivo animal studies and Phase I trials ∗ PK/PD, ADME(T) ∗ Study of site, specificity, mechanism of action of new pharmaceuticals * Preclinical study of dose regimen, toxicity,… → faster screening of lead compounds (< time) → earlier decisions about compound’s suitability (< cost ) → smaller number of animals R. Lecomte − Ohrid 2018 Workshop − July 25-28, 2018 4 Preclinical Imaging In vivo Non-invasive Allows longitudinal follow up studies in same animal Primarily anatomical Primarily molecular Ultrasound (US) Optical (fluorescence, bioluminescence) Magnetic resonance (MRI) Single Photon Emission Computed Computed tomography (CT) Tomography (SPECT) Positron Emission Tomography (PET) R. Lecomte − Ohrid 2018 Workshop − July 25-28, 2018 5 The Challenge of Preclinical Imaging Na 18 F Bone Scans ×××1/300 ×××1/10 75 kg human 200 g rat 20 g mouse Clinical PET scanner Preclinical PET scanner Mouse PET scanner (5-6 mm or ~1 cc) (1.3 mm or ~2 µl) (0.8 mm or ~0.5 µl) R. Lecomte − Ohrid 2018 Workshop − July 25-28, 2018 6 A Anatomical Preclinical Imaging Modalities F Functional M Ultrasound Optical Molecular (Bioluminescence, fluorescence) Structure A 0.1 mm A Topography F Doppler µm to mm CT M Tissue Density, Z 3 A ~10 cells 20-50 µm ≠≠≠ quantitative F Fluoroscopy PET/SPECT F M MRI Radiotracer A F M ~1-2 mm H Concentration 0.1 mm <10 -12 mole BOLD, DCE = quantitative βββ-galactocidase 0.1 µmole H / µmole 31 P R. Lecomte − Ohrid 2018 Workshop − July 25-28, 2018 7 In Vivo Pre-Clinical Imaging Modalities MODALITY PARAMETERS RESOLUTION SENSITIVITY APPLICATIONS OPTICAL Metabolism, Receptors, Tumor µm (in situ ) ~10 2-3 cells Fluorescence Visible/IR light progression, Gene expression, mm (external) 10 -9-10 -15 M Bioluminescence Therapy assessment Raman, IVM Acoustic impedance Anatomy, Blood flow 10 -15 US Speed / Attenuation <100 µm Tissue structural (mic robubbles) Photoacoustic Frequency shift characteristics Anatomy Density ~20-50 µm ~µg Mineral content X-Ray CT Z Contrast media 1H concentration 0.1 µmole 1H Anatomy 31 MRI / MRS T1 & T 2 relaxation 25-100 µm µmole P Blood Flow Chemical shifts (>10 16 atoms) Conc./ Chemical State Blood flow/volume, Perfusion SPECT Radiotracer µSPECT 0.1-2 mm 10 -12 mole Metabolism, PK/ADME 11 PET concentration µPET 1-2 mm (>10 atoms) Receptor concentration, Gene expression, Therapy assessment IVM: IntraVital Microscopy; US: UltraSound; CT: Computed Tomography; MRI/MRS: Magnetic Resonance Imaging/Spectroscopy; SPECT: Single Photon Emission Computed Tomography; PET: Positron Emission Tomography. R. Lecomte − Ohrid 2018 Workshop − July 25-28, 2018 8 The Molecular Imaging Matrix* CT MRS Resolution Limit Range *Adapted from: SR Meikle et al , Small animal SPECT and its place in the matrix of molecular imaging technologies, Phys Med Biol 50:R45-R61;2005 JC Gore JC et al , Molecular imaging without radiopharmaceuticals? J Nucl Med 41(3):332-8;2009 R. Lecomte − Ohrid 2018 Workshop − July 25-28, 2018 9 Ultrasound Imaging Vevo 2100 High-frequency US Photoacoustic high-frequency micro-US system from Visualsonics Strengths: Portable Inexpensive High spatial & time resolution Non-targeted Targeted Truly real-time (blood flow) Good depth penetration µbubbles contrast agent Clinically translatable Weaknesses: Limited to soft tissues (no bone or air structures) James & Gambhir. A molecular imaging primer: modalities, Probe coupling to subject imaging agents, and applications. Physiol Rev 92:897-965;2012 Operator dependent R. Lecomte − Ohrid 2018 Workshop − July 25-28, 2018 10 Magnetic Resonance Imaging (MRI) Pre-clinical MRI: 4-11T (Earth magnetic field: 0.00003T) Larmor frequency (H): !ͤ Ɣ ̼ͤ 1.5T: !ͤ Ɣ 64 ͇͂ͮ 7T: !ͤ Ɣ 300 ͇͂ͮ With imaging agent Pre-clinical MR scanner (SPIO) Strengths: High spatial resolution High soft-tissue contrast No ionizing radiation Weaknesses: High cost (>1 M$) Poor sensitivity Long acquisition time James & Gambhir. A molecular imaging primer: modalities, imaging agents, and applications. Physiol Rev 92:897-965;2012 R. Lecomte − Ohrid 2018 Workshop − July 25-28, 2018 11 Small Animal 7 Tesla MRI 7T MRI facility at the Sherbrooke Molecular Imaging Center R. Lecomte − Ohrid 2018 Workshop − July 25-28, 2018 12 7T MRI Cerebral Imaging Rat brain vascularisation Resovist (blood pool agent) T2* Weighting Resolution: 117 µm Acquisition time: 30 min In vivo Ex vivo Courtesy M. Lepage Université de Sherbrooke R. Lecomte − Ohrid 2018 Workshop − July 25-28, 2018 13 Pharmacokinetic modeling with Gd-DTPA/MRI vs FDG/PET Volume transfer constant Extravascular volume fraction Blood volume fraction Arterial input function measured with FDG and Gd-DTPA Poulin et al , Magn Reson Med 2012 10.1002/mrm.24318 R. Lecomte − Ohrid 2018 Workshop − July 25-28, 2018 14 Optical Imaging Bioluminescence Fluorescence Emerging variants • Cerenkov imaging • Raman imaging • Photoacoustic imaging • Intravital microscopy • Etc. Strengths: Inexpensive High sensitivity Multiplexing capabilities Weaknesses: Poor spatial resolution Pre-treatment Limited depth (mm to ~cm) Non-quantitative (Surface weighted images Post-treatment James & Gambhir. A molecular imaging primer: modalities, imaging agents, and applications. Physiol Rev 92:897-965;2012 R. Lecomte − Ohrid 2018 Workshop − July 25-28, 2018 15 Principle of µCT • Digital X-ray camera DETECTOR • Phosphor (GOS) or CsI on CCD or CMOS photodiode or a-Si sensor matrix • µfocus 10-100µm • W or Mo anode • MOS Flat panel CONE • A-Se on TFT or CMOS BEAM • 20-80 KV readout array • 0.1-5 mA • Be filter • Semiconductor pixel detector array* • Resolution: 10-100 µm * B. Mikulec, “Development of segmented semiconductor arrays for quantum imaging”, Nucl. Instrum. Meth. Phys. Res. A510, pp. 1-23, 2003. R. Lecomte − Ohrid 2018 Workshop − July 25-28, 2018 16 CT Measurement Process Transmission through tissues n I === I 0 exp −−−x ∑∑∑µµµi i===1 n I0 ln === x ∑∑∑µµµi I i===1 R. Lecomte − Ohrid 2018 Workshop − July 25-28, 2018 17 CT Measurement Image Display: Black +1000 ⇒ CT numbers* or Hounsfield Units (HU) µi − µwater Ni = 1000 × µwater ⇒ Diagnostic quality ~5-10 HU (~1% SD) * From G. Michael, “X-ray computed tomography”, Physics Education 36 (11), pp. 442-451, November 2001. White R. Lecomte − Ohrid 2018 Workshop − July 25-28, 2018 18 µCT Spatial Resolution 2 2 FWHM total ≈ FWHM d + FWHM x x 1 ∆ FWHM M X FWHM d ≈ 2.35 x ≈ × f M 2 FWHM d : detector resolution FWHM x : projection blurring due to X-ray focal spot size Dx Xf ∆x : pixel size Xf : focal spot size (FWHM) M : Magnification M = (dxs + dsd ) / dxs * M.J. Paulus et al., “High resolution X-ray computed tomography: an emerging tool for small animal cancer research”, Neoplasia 2(1-2), pp. 62-70, 2000 R. Lecomte − Ohrid 2018 Workshop − July 25-28, 2018 19 X-ray Energy in µCT Attenuation Coefficient vs Energy Contrast Resolution vs Energy* 1000 ) -1 Bone Soft Tissue 100 Fat Water 10 1 Attenuation Coefficient (cm 0.1 0 20 40 60 80 100 X-ray Energy (keV) • At low energy (µ ↑↑↑↑↑↑ ) contrast resolution limited by attenuation in subject • At higher energies (µ ↓↓↓↓↓↓ ) contrast resolution limited by low absorption in subject • Best contrast resolution at energy for which µ ~ 2/D • For rats (D ~ 5-6 cm), Eopt ~ 30 keV; for mice (D ~ 2.5-3 cm), Eopt ~ 20 keV • Most studies performed at E ~ 40-60 keV * M.J. Paulus et al., “High resolution X-ray computed tomography: an emerging tool for small animal cancer research”, Neoplasia 2 (1-2), pp. 62-70, Jan-April 2000. R. Lecomte − Ohrid 2018 Workshop − July 25-28, 2018 20 µCT Systems SkyScan-1078 ImTek MicroCAT II Stratec XCT Research SA GE eXplore RS R. Lecomte − Ohrid 2018 Workshop − July 25-28, 2018 21 Applications of µCT µCT Skeleton Image • Anatomy - Skeletal tissue - Adipose tissue - Thoracic imaging • Contrast enhanced soft tissue imaging - Vascular morphology - Abdominal tumor imaging - Renal morphology and function • Tissue density • Tissue composition http://www.imtekinc.com/html/skeletal.html R. Lecomte − Ohrid 2018 Workshop − July 25-28, 2018 22 Volume Rendering of Mouse Skull À trouver D0 D9 C. Lackas, https://commons.wikimedia.org/w/index.php?curid=5791359 R. Lecomte − Ohrid 2018 Workshop − July 25-28, 2018 23 Lung Tumor Follow-up in Mouse by CT D0 D9 Kirsch et al, Int J Radiat Oncol Biol Phys 76:973–977, 2010 R. Lecomte − Ohrid 2018 Workshop − July 25-28, 2018 24 Contrast Agent in CT Imaging Longitudinal micro-CT imaging of liposomal iodine biodistribution. Liposomes slowly accumulate in the subcutaneous tumor, liver, and spleen overD0 the course of 72 h. The white arrow points to the location of the D9 tumor in each image. Ashton et al, In vivo small animal micro-CT using nanoparticle contrast agents, Front Pharmacol 00256, 2015 R. Lecomte − Ohrid 2018 Workshop − July 25-28, 2018 25 Contrast Agent in CT Imaging EGFR- expressing tumors 3D micro-CT reconstructions of mice with EGFR-expressing tumors. Mice were injected with (A) saline, D9(B) non-targeted gold nanoparticles (GNPs), or (C) EGFR-antibody targeted gold nanoparticles.