Table 1.
Summary of the advantages and limitations of the use of the MRI technique in ocular drug-delivery research and comparison with the traditional ocular pharmacokinetics method of eye enucleation and dissection
| MRI | Traditional pharmacokinetics | |
|---|---|---|
| Type | Non-invasive | Invasive |
| Procedure | Continuous monitoring over time without killing the animal | Killing the animal and dissecting the eye at different time points |
| Molecule/drug | Can only monitor contrast agent or certain molecules. Selective monitoring | All types of molecules as long as tissue assay is available. Require assay development |
| Spatial resolution | Can monitor 3D distribution of small volume, but resolution may not be high enough to determine the concentration in thin tissues | Cannot evaluate 3D distribution of small finite volume, but can determine amount in small tissues (through dissection) |
| Temporal resolution | Limited by scan time, which is related to spatial resolution | Limited by the time of dissection. Tissue can be frozen to avoid molecule redistribution. Redistribution in tissue during dissection can be an issue. |
| Errors | Variability due to MRI hardware, experimental setup, and technique. Partial volume averaging effect. Relaxation times affected by tissue and microenvironment such as temperature and viscosity | Possible cross-contamination among tissues during dissection. Inherited errors from analytical techniques in tissue assay. Can be less variable than MRI |
| Sensitivity and detection limit | Relatively low compared with conventional assay techniques such as HPLCa and GC | High sensitivity and good limit of quantification to detect low concentration |
| Human clinical study | Possible with approved contrast agents and/or 19F MRS/MRI of the fluorinated drug compound | Difficult and not feasible with healthy subjects |
| Resource and cost | Expensive equipment is required. Special hardware is sometimes needed, such as 19F MR. Only a small number of animals is needed | Skillful researchers to perform precise dissection. Require a large number of animals |
a
HPLC, high-performance liquid chromatography; GC, gas chromatography.