High transmitter bandwidth can be used effectively to reduce scan times in claustrophobic and moving patients. Practical applications of high transmitter bandwidth (Fast mode) MRI conditional pacemakers, heart valves. Low transmitter bandwidth RF pulses are also useful for scanning patients with MRI conditional implants e.g.
Low SAR mode must be chosen while scanning pregnant patients to avoid any potential RF harm to the foetus. Low transmitter bandwidth mode is the most appropriate option to choose when scanning neonates and sedated patients due to their inability to feedback to the operator. Practical applications of low transmitter bandwidth (Low SAR mode) It should be noted that a Fast RF pulse will have a higher chance of peripheral nerve stimulation. It has shorter echo spacing (ES) and very minimal susceptibility and distortion artefacts. This RF pulse type will provide the user an opportunity to reduce TEs and TRs. This is a high bandwidth RF pulse with compromised slice profile and will give a higher SAR compared to the other modes. This is a medium bandwidth RF pulse with good slice profile and optimized SAR behaviour. Also, low transmitter bandwidth pulse type is more susceptible to susceptibility and distortion artefacts. A disadvantage of the low SAR RF pulse type are long scan times due to longer minimum TEs, TRs and echo spacing (the time from one echo to the next echo). Choosing this option reduces the chance of the sequence going into first level mode. This RF pulse type will give reduced SAR values. This option will allow you to choose the lowest possible slice thickness in most pulse sequences. This is a low bandwidth RF pulse with very good slice profile and allows less crosstalk between slices. A low specific absorption rate (SAR) option which is the low bandwidth pulse, a normal option which is the medium bandwidth pulse and a Fast option which is the higher bandwidth pulse. Siemens scanners offer three type of RF pulses in most of their sequences. the higher the transmitter bandwidth higher the lowest possible slice thickness. The lowest possible slice thickness of a pulse sequence is directly proportional to the transmitter bandwidth of the RF pulse type i.e. This is used to excite a discrete slice thickness or volume. Transmitter bandwidth is the bandwidth used during the transmission of RF pulses. Transmitter bandwidth describes the properties of transmitted radiofrequency (RF) pulses and receiver bandwidth describes the quality of MRI signal. An MRI sequence is designed with two types of bandwidths: transmitter bandwidth (tBW) and receiver bandwidth (rBW). Bandwidth is measured in cycles per second or Hertz (Hz). In MRI bandwidth is defined as the amount of frequencies or wavelengths that can be transmitted or received in a limited amount of time.
0 kommentar(er)
