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enh: add suggestions from review
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eilidhmacnicol committed May 5, 2022
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Expand Up @@ -11,24 +11,24 @@ difficult to obtain.

## Hardware
### Magnet field strength
The scanner's field strength, which range from 4.7 to 16.4 Tesla, can itself
The scanner's field strength, which typically ranges from 4.7 to 16.4 Tesla for preclinical imaging, can itself
have many impacts on the data quality: higher field strength
provides higher signal-to-noise ratios in shorter acquisition times, but it also
provides higher signal-to-noise ratios, but it also
exacerbates many types of artifacts.
### Scanner manufacture
Bruker currently has a monopoly in preclinical imaging, but many sites have older scanners from other manufacturers.
Those with Bruker scanners may also have a maintenance package which includes tests
for quality assurance.
### Coils
Volume coils require manual tuning (at least) daily.
Some volume coils require manual tuning.
For scanners from out-of-business manufacturers, "homemade" coils are more common
and less standardised.
Cryocoils are increasingly available but not yet ubiquitous.
### Physiological monitoring
While the requirements for accurate physiological monitoring is explained in more
detail below, there are many pieces of hardware that can be discussed.
This minimally includes rectal thermometers and respiration balloons, but can also
include pulse oximeters and/or invasive blood pressure monitoring.
include pulse oximeters and/or invasive blood pressure monitoring.
### Other hardware_
Cradles, bite bars, ear bars, pillows can be provided by the scanner manufacturer or
"homemade".
Expand All @@ -39,14 +39,13 @@ These facilitate support of the animal in the scanner and reduce movement.
Related to scanner manufacture, is the software used to acquire and reconstruct
the images.
Bruker's software, Paravision, has several versions available.
Paravision generates `2dseq` files rather than the `DICOM` images commonly
Paravision generates `2dseq` files and can export `DICOM` images commonly
generated by human scanners.
Consequently, conversion to standardised naming formats requires specialised
software that can work with these proprietary files.
However, storage of metadata may not always be consistent with human imaging standards.
### Other software
Similarly, various software is available for monitoring physiology which is
discussed at length [below](#physiology).
As the animals are often anaesthetised task-based fMRI is less common.
As the animals are often anaesthetised, task-based fMRI is less common.
Instead, experiments may generate evoked-responses to some stimulus (e.g.
stimulating a paw with electricity) in the scanner.
Thus, software is also required to synchronise the stimulus onset to the scanning
Expand All @@ -64,7 +63,7 @@ still.
This difference in scale necessitates the increased magnet field strength but the change in field strength is not proportional to the change in size.
### Tissue differences
The proportion of white matter in rodents is smaller than that in humans.
Since white matter bundles are much less distinct in rats and mice, the MR
Since white matter bundles are much less distinct in rats and mice, the MR
signal contrast between the two tissue types is often less well-defined.

Additionally, the olfactory bulb is much larger in rodents than in humans and there
Expand All @@ -78,8 +77,7 @@ equivalent.
Additionally, I have noticed confusion in the convention for naming the scanner
orientations.
Humans most often enter the scanner supine along the axis that aligns
with that of B0 so the B1 field aligns with the anterior-posterior plane, and the
B0 field axis aligns with the superior-inferior axis.
with that of B0, i.e., the B0 field axis aligns with the superior-inferior axis.
Rodents are likely to be prone (although not always) and because of the difference
in anatomical orientation described above, the posterior-anterior plane in
quadripeds aligns with the B0 field axis.
Expand All @@ -88,7 +86,7 @@ Thus orientation may be "scanner-oriented" (where the axes aligns with the magne
field directions) or "subject-oriented" (where the axes align with the anatomy of
the subject).
### Strain
There may be differences in anatomy or physiology that come from differences in
There may be differences in anatomy or physiology that come from differences in
species strain.
In particular, genetically modified animals may be more susceptible to larger
ventricular compartments.
Expand All @@ -104,8 +102,8 @@ with benefits and costs.
Compound | Administration | Benefits | Costs
--- | --- | --- | ---
Isoflurane | inhalation | <li> non-invasive administration</li><li>Short recovery</li>|<li>Uncouples BOLD response</li><li>Dangerous cumulative effects</li>
(Dex)meditomidine | infusion | <li> preserves BOLD response </li> | <li> requires cannulation</li><li>requires Atipamezole for speedy recovery</li>
Alpha-Chloralose | infusion |<li> preserves BOLD response </li> | <li>Difficult recovery</li>
(Dex)meditomidine | infusion | <li> preserves BOLD response </li> | <li>requires Atipamezole for speedy recovery</li>
Alpha-Chloralose | infusion |<li> preserves BOLD response </li> | <li> requires cannulation</li><li>Difficult recovery</li>
Ketamine | infusion | |

### Respiration
Expand All @@ -121,16 +119,16 @@ Consequently, internal body temperature is recorded with a thermometer.
It is possible to use the thermometer reading as part of a feedback loop
controlling either a water heating system (built in to the bed or applied as a
heated blanket) or an air heating system (which is blown through the scanner bore
with a fan).
with a fan) with all the possible problems related to frequency shifts and drifting that could affect the scans.

Since temperature is critical for the rate of oxygen consumption, temperature should be maintained within a small normative range.
### Movement
Movement is often reduced in scanning animal imaging due to the use of bite bars,
Movement is often reduced in animal imaging due to the use of bite bars,
ear bars, and anaesthesitics and sedatives.
However, movement should still be carefully scrutinized as it may point to:
- less anaesthetised/sedated state
- movement associated with the onset of a task (e.g. jumping at stimulus)
- scanner drift
- scanner drift

## Hands-on
Let's see some of these factors in action.
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