Inversion Time (TI)
Inversion Time
In MRI (Magnetic Resonance Imaging), TI stands for “Inversion Time.” It refers to the time interval between the application of an inversion pulse and the acquisition of MRI signal. TI (Inversion Time) is used in certain pulse sequences to manipulate the contrast between different tissues in the image.
The inversion recovery technique involves applying an inversion pulse to the body tissues, which inverts the longitudinal magnetization. After a certain TI, a subsequent excitation pulse is applied to generate the MRI signal. The choice of TI determines the contrast between different tissues in the resulting image.
By adjusting the TI, it is possible to enhance the contrast between different types of tissues. For example, in brain imaging, a longer TI might be used to suppress the signal from cerebrospinal fluid (CSF) and highlight abnormalities in surrounding brain tissues. Shorter TIs, on the other hand, can emphasize the contrast between different types of tissues, such as white matter and gray matter.
Brain image with a TI of 2500ms
Foot image with a TI of 150ms
Use of TI in brain imaging
Different TI values are utilized in brain imaging, and the optimal choice depends on the specific clinical requirements and desired image contrast. Here are commonly employed TI values in brain MRI and their respective purposes:
Long TI (e.g., 2000-2500 ms): Longer TI values are utilized to nullify the signal from cerebrospinal fluid (CSF) and accentuate the contrast between gray matter (GM) and white matter (WM). This aids in distinguishing and defining brain structures, as well as detecting subtle abnormalities.
Short TI (e.g., 13-180 ms): Shorter TI values enhance contrast between various tissue types, including GM, WM, and pathologies. Additionally, shorter TI values are effective in suppressing fat signal in the skull and visualizing skull lesions.
Intermediate TI (e.g., 600-1000 ms): Intermediate TI values strike a balance between GM, WM, and other brain structures. They offer a compromise by maximizing tissue contrast while maintaining adequate signal-to-noise ratio.
TI 150
TI 900
TI 2500
Use of TI in MSK imaging
In MSK imaging, TI (Inversion Time) plays a crucial role in suppressing fat signals. A frequently employed technique is the “STIR” (Short TI Inversion Recovery) or “FS” (Fat Suppression) sequence, which typically utilizes a TI value of approximately 150-180 ms.
The specific choice of a TI around 150-180 ms in STIR MRI aims to nullify the signal emitted by fat tissues while preserving or enhancing the signal from water-containing tissues. By eliminating the influence of fat signals, the STIR sequence effectively highlights areas exhibiting edema, inflammation, or fluid accumulation. This proves beneficial in evaluating a range of musculoskeletal conditions, including bone marrow edema, joint inflammation, and soft tissue pathologies.
TI 150ms C SPINE image
TI 150ms neck image
TI 150ms foot image
References
- Bushong, S. C. (2017). Magnetic Resonance Imaging: Physical and Biological Principles (4th ed.). Elsevier.
- Haacke, E. M., Brown, R. W., Thompson, M. R., & Venkatesan, R. (2014). Magnetic Resonance Imaging: Physical Principles and Sequence Design. John Wiley & Sons.
- Parker, J. R. (2011). Inversion recovery imaging. American Journal of Roentgenology, 196(4), W449-W455.
- Kim, D. H., Sohn, C. H., Kim, S., Lim, K. S., Kim, M. J., & Shin, B. S. (2016). Application of inversion recovery sequences for hepatic arterial phase magnetic resonance imaging. World Journal of Gastroenterology, 22(38), 8481-8490.
- Ibrahim, T. S., & Lee, R. (1997). Inversion recovery EPI in functional MRI in human brain at 1.5 T and 3.0 T. Magnetic Resonance in Medicine, 38(1), 21-26.