# Cardiac Diffusion Tensor Biomarkers of Chronic Infarction Based on In Vivo Data
## 2 Methods  
### Animal Model and Infact Induction  
Animal care during infarct induction, imaging, and all experimental procedures followed protocol #2015-124 approved by the Institutional Animal Care and Use Committee of the University of California, Los Angeles. These experiments were part of a larger study, whose scope is to characterize myocardial structure and function [15], and to identify the material behavior of the passive myocardium [16]. As part of this study, an infarct model was created using female Yorkshire swine subjects. In vivo and/or ex vivo MRI data necessary for the current study was successfully acquired in seven (N = 7) subjects. All subjects (N = 7) were included in the ex vivo analysis. Two subjects were excluded from the in vivo analysis since: (1) one subject died during MRI acquisition before in vivo cDTI data could be acquired; and (2) one subject presented a right ventricle infarct that was not visible on in vivo cDTI data due to the poor in vivo cDTI quality in the right ventricle. The remaining five (N = 5) subjects were considered for in vivo analyses. Before the beginning of the experimental procedures, the animal subjects had time to acclimate for at least one week. At the time of the MRI exam, the subjects' body weight was 59.5 kg \(\pm\) 6.6 kg (mean \(\pm\) standard deviation). Myocardial infarction was induced under general anesthesia using microspheres. Ketamine (12.5 mg/kg) and midazolam (1 mg/kg) were injected intramuscularly to induce anesthesia. After induction, carprofen (4 mg/kg) and buprenorphine (0.02 mg/kg) were administered intramuscularly to provide pre-emptive analgesia. During MRI, anesthesia was maintained using isoflurane (1.5-2%) and Lactated Ringer's solution was administered (2-5 mL/kg/h). After accessing the femoral artery using a Seldinger technique, a balloon wedge pressure catheter (\(\mathcal{T}\) French) was inserted and guided to the aortic sinus using a metal guidewire under X-ray fluoroscopy. Subsequently, a micro guidewire (0.014 inches) was used to select a branch of the left circumflex (LCx) or left anterior descending (LAD) artery and a balloon catheter (1.5 mm diameter) was inserted and inflated prior of injecting a volume of microspheres (90 \(\upmu\)m Polystyrene microspheres) equal to 2.5-3.0 mL. After one minute to avoid microsphere backflow, the balloon catheter was deflated and extracted. In vivo imaging was conducted six to ten weeks after infarct induction to allow for the formation of scar tissue. Additional details regarding the experimental procedure may be found in [17]. A 3T MRI scanner (Prisma, Siemens Healthineers, Erlangen, Germany) was used for in vivo and ex vivo imaging. In vivo imaging protocols included: late gadolinium enhancement (phase-sensitive inversion recovery sequence, TE/TR = 1.6 ms/876 ms; flip angle = 20\({}^{\circ}\); spatial resolution = 1.33 \(\times\) 1.33 \(\times\) 8.0 mm\({}^{3}\), \(N_{\mathrm{avg}}=1\)), T1-mapping (modified look-locker inversion recovery sequence with motion correction, TE/TR = 1.04 ms/280.69 ms; flip angle = 30\({}^{\circ}\); spatial resolution = 1.77 \(\times\) 1.77 \(\times\) 8.0 mm\({}^{3}\), \(N_{\mathrm{avg}}=1\)), and cDTI (M1M2-nulled motion-compensated waveform sequence [18], TE/TR = 59 ms/5000 ms; flip angle = 90\({}^{\circ}\); spatial resolution = 2.0 \(\times\) 2.0 \(\times\) 8.0 mm\({}^{3}\); b-values = 0 s/mm\({}^{2}\) and 350 s/mm\({}^{2}\); \(N_{\mathrm{dir}}=12\); \(N_{\mathrm{avg}}=30\)). At the end of the in vivo MRI exam and before euthanasia, subjects were injected with a double dose of gadolinium-based contrast agent (0.6 mL/kg gadopentate dimeglumine and 10 mL of saline solution). Euthanasia solution (0.1 mL/lb, Euthanosl\({}^{\mathrm{B}}\), Virbac, Carros, France) was administered after 10 min to allow the circulation of the contrast agent. Hearts were then extracted, rinsed, and prepared for ex vivo imaging. To preserve ventricular geometry, the hearts were inserted into 3D-printed molds based on images acquired at mid-diastasis [19].