Iohexol

Dynamic Contrast Enhanced Micro-CT Angiography Protocol
1. Pre-experiment Preparation
(1) Weigh BALB/c mice (8-12 weeks old), and calculate the Iohexol dose: 25µl/g (=7.5mgI/g).
(2) Prepare the anesthetic mixture, sterilize with a 0.2µm filter, store the mixture in the dark at 4°C, and use immediately after preparation.
(3) 5ml of Iohexol (300mgI/ml) is added to 5ml of sterile saline and mixed to obtain 10ml of 150mI/ml working solution, sterilized with a 0.2µm filter, stored in the dark, and used immediately after preparation.
(4) Draw Iohexol into a 1ml syringe, expel air bubbles, and attach Iohexol to the injection pump. Set the flow rate: total injection volume (µl) = 25µl × body weight (g). Injection time = 45s → flow rate (µl/s) = total volume/45.
(5) Fix the mouse on a heating pad (37°C), and monitor the rectal temperature in real time to maintain it at 36.5-37.5°C.
2. Intravenous Injection
(1) Wipe the mouse tail's posterior 1/3 with an alcohol swab, and use an infrared lamp to assist in dilating the tail vein.
(2) Insert the indwelling needle, confirm the return of blood, and fix; connect the other end of the catheter to the injection pump extension tube filled with Iohexol.
(3) Slowly inject 20µl of 0.9% NaCl to verify that the channel is unobstructed without leakage.
3. Dynamic Contrast Scanning Procedure
(1) First, collect the "pre-contrast" baseline sequence (example parameters: 80kV; 500µA; 360-degree projection; 10min).
(2) Start the scan and trigger the injection pump simultaneously; immediately begin the first round of "post-contrast" scan after the injection is completed (45s).
(3) Repeat the post-contrast scan every 50s for a total of 5 periods; the entire process takes approximately 4.5min.
(4) After the scan, slowly remove the needle, apply local pressure to stop bleeding for 30s; place the mice on the heating pad to recover, and return the mice to the cage once the righting reflex returns.
4. Postoperative Observation
(1) Observe breathing, skin color, and activity at 0, 30, and 60min, record any adverse reactions (convulsions, respiratory depression, etc.).
(2) Provide 5% glucose water within 24h to aid iodine excretion.
(3) If multiple contrast scans are needed, the interval should be ≥ 72h, and monitor serum creatinine to assess renal function.
5. Precautions
(1) Iohexol is a low-osmolar non-ionic contrast agent and can be stored at room temperature; check for crystallization before use, and if present, dissolve Iohexol in a 37°C water bath.
(2) The depth of anesthesia should be such that there is no withdrawal reflex when the toe is pinched; too deep anesthesia can cause respiratory depression, and too shallow can result in motion artifacts.
(3) If the experimental period is > 1h, administer 0.3ml of warm saline intraperitoneally every 20min to prevent dehydration and hypotension.

References:
[1] Yan D, Zhang Z, Luo Q, et al. A novel mouse segmentation method based on dynamic contrast enhanced micro-CT images[J]. PLoS One, 2017, 12(1): e0169424.