Journal Club: Round window injection of contrast enhancing agent to visualise guinea pig cochlea.

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Today's journal article

Zhou C, Feng SJ, Leong S, Breil E, Voruz F, Valentini C, Hammer DR, Aksit A, Olson ES, Guo J, Kysar JW, Lalwani AK. Contrast Enhancement of Cochlea after Direct Microneedle Intracochlear Injection of Gadodiamide through the Round Window Membrane with Minimal Dosage. 

Why I picked this article

Because the cochlea is such a small organ, imaging the cochlea with Magnetic resonance imaging (MRI) is very challenging. MRI technique can be combined with the use of "contrast agent" which can enhance visualisation. Researchers and clinicians have used contrast agents administered via intravenous injection or intratympanic (= via ear canal) injection to image endolymphatic hydrops. However, the enhancement can be variable. 

This research aimed to test a proof-of-concept to use a tiny microneedle to directly inject a contrast-enhancing agent into the guinea pig cochlea. 

Some of the research findings

Animal Model: 
  • Hartley guinea pig 
  • Animals were euthenized either 5 min after surgical administration of the contrast agent (group 1), or before the administration (group 2).
Delivery of contrast agent:
  • a 100 μm-diameter microneedle (35 μm lumen) was used.
  • A microneedle was passed through the round window membrane to inject the contrast agent.
  • 1 μL of diluted gadodiamide (17.4 mM, diluted in artificial perilymph) was administered.
MRI imaging: 
  • serial 9.4 T small-animal MRI post-mortem
  • Early appearance: contrast was already visible in the basal turn of both ST and SV on the first scan, as early as 35 min after injection. 
  • By 60 min: contrast reached the first two turns of ST and SV.
  • By 90 min: contrast reached the second half of the third turns and the apical turns of ST and SV.

From part of Fig 3. Zhou et al 2025.

Haruna's takeaway

This is a very interesting study, and to be honest, for MRI, beautiful visualisation and segmentation of the guinea pig cochlea (which is tiny!). I didn't quite get why the imaging had to be done post-mortem... was it due to the fact that animals could not be maintained under anaesthesia in MRI? Gadolinium-based contrast-enhancing agent has safety concerns, as the researchers of this publication point out as limitations. What we need is a chemist to come up with a very novel, safe and easy to administer contrast-enhancing agent....! 

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This is Haruna's 85/100 of the 100-day challenge to post a science blog article every day! I love inner ear biology & cochlear physiology.