the categories under each section. It is possible that all the categories are relevant if the examination is being performed for the first time. However, there may be occasions when only one item is appropriate. For example, there could be a specific artefact that is regularly observed in chest examinations, or image quality is not up to standard in lumbar spine protocols. Under these circumstances, read the subsection entitled Protocol optimization.
If the terms used, or concepts discussed in Part 2 are unfamiliar, then turn to Part 1 and read the summaries described there.
2 Protocol Parameters and Trade‐offs
INTRODUCTION
This section refers mainly to the Technical issues subheading discussed under the Protocol optimization heading considered for each examination in Part 2. Only a brief overview is provided here. For a more detailed explanation, please refer to Chapter 7 of the fifth edition of MRI in Practice or an equivalent text.
The main considerations of protocol optimization are:
signal‐to‐noise ratio (SNR)
contrast‐to‐noise ratio (CNR)
spatial resolution
scan time.
Each factor is controlled by certain protocol parameters, and each ‘trades off’ against the other. This section summarizes these parameters and their trade‐offs. Suggested protocol parameters are outlined in Table 2.1 and should be universally acceptable on most systems. However, weighting parameters are field strength dependent, and therefore some modification may be required for extremely low‐ or high‐field systems.
Table 2.1 Summary of parameters.
Source: Catherine Westbrook and John Talbot, MRI in Practice, 5th ed., John Wiley & Sons, 2019.
| 1.5 T | 3T | |||
|---|---|---|---|---|
| CSE | CSE | |||
| Short TE | Minimum–30 ms | Short TE | Minimum–15 ms | |
| Long TE | 70 ms+ | Long TE | 70 ms+ | |
| Short TR | 300–700 ms | Short TR | 400–800 ms | |
| Long TR | 2000 ms+ | Long TR | 2500 ms+ | |
| FSE/TSE | FSE/TSE | |||
| Short TE | Minimum – 20 ms | Short TE | Minimum–15 ms | |
| Long TE | 90 ms+ | Long TE | 90 ms+ | |
| Short TR | 400–600 ms | Short TR | 400–600 ms | |
| Long TR | 4000 ms+ | Long TR | 4000 ms+ | |
| Short ETL/TF | 2–6 | Short ETL/TF | 2–6 | |
| Long ETL/TF | 20+ | Long ETL/TF | 20+ | |
| IR T1 | IR T1 | |||
| Short TE | Minimum–20 ms | Short TE | Minimum–20 ms | |
| Long TR | 3000 ms+ | Long TR | 3500 ms+ | |
| TI | Short or null time of tissue | TI | Short or null time of tissue | |
| Short ETL/TF | 2–6 | Short ETL/TF | 2–6 | |
|
STIR
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