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INTRODUCTION
ОглавлениеThis 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 | STIR | ||
| Long TE | 60 ms+ | Long TE | 60 ms+ |
| Long TR | 3000 ms+ | Long TR | 3000 ms+ |
| Short TI | 100–175 ms | Short TI | 210 ms |
| Long ETL/TF | 20+ | Long ETL/TF | 20+ |
| FLAIR | FLAIR | ||
| Long TE | 80 ms+ | Long TE | 80 ms+ |
| Long TR | At least 4× TI | Long TR | At least 4× TI |
| Long TI | 1700–2500 ms | Long TI | 1700–2500 ms |
| Long ETL/TF | 20+ | Long ETL/TF | 20+ |
| Rewound GRE | Rewound GRE | ||
| Long TE | 10–15 ms | Long TE | 10–15 ms |
| Short TR | <50 ms | Short TR | <50 ms |
| Flip angle | 30° to 45° | Flip angle | 30° to 45° |
| Spoiled GRE | Spoiled GRE | ||
| Short TE | Minimum | Short TE | Minimum |
| Short TR | <50 ms | Short TR | <50 ms |
| Flip angle | 30° to 45° | Flip angle | 30° to 45° |
| Balanced GRE | Balanced GRE | ||
| Short TE | Minimum | Short TE | Minimum |
| Short TR | Minimum | Short TR | Minimum |
| Flip angle | >35° | Flip angle | >35° |
| Reverse echo GRE | Reverse echo GRE | ||
| TE (effective) | Minimum | TE (effective) | Minimum |
| Short TR | <50 ms | Short TR | <50 ms |
| Flip angle | 30° to 45° | Flip angle | 30° to 45° |
| 1.5T and 3T | |||
| Slice thickness 2D | Slice thickness 3D | ||
| Thin | <1 mm/1 mm | Thin | <1 mm/1 mm |
| Medium | 2 –4 mm | Thick | 2–4 mm |
| Thick | 5 mm+ | ||
| FOV | Matrix | ||
| Small | <160 mm | Coarse | <256 × 128 |
| Medium | 160–300 mm | Medium | 256/512 × 256 |
| Large | 300 mm+ | Fine | 512 ×512 |
| Very fine | >1024 × 1024 | ||
| NEX/NSA | Slice number 3D | ||
| Low | 1 or less | Small | <32 |
| Medium | 2–3 | Medium | 64 |
| High/multiple | 4+ | Large | >128 |
| PC‐MRA 2D and 3D | TOF‐MRA 2D | ||
| TE | Minimum | TE | Minimum |
| TR | 25–33 ms | TR | 28–45 ms |
| Flip angle | 30° | Flip angle | 40°–60° |
| VENC venous | 20–40 cm/s | ||
| VENC arterial | 60 cm/s | TOF‐MRA 3D | |
| TE | Minimum | ||
| TR | 25–50 ms | ||
| Flip angle | 20°–30° |
