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Abstract
Purpose
To investigate the temperature-based differences of cortical bone ultrashort echo time MRI (UTE-MRI) biomarkers between body and room temperatures. Investigations of ex vivo UTE-MRI techniques were performed mostly at room temperature however, it is noted that the MRI properties of cortical bone may differ in vivo due to the higher temperature which exists as a condition in the live body.
Materials and Methods
Cortical bone specimens from fourteen donors (63 ± 21 years old, 6 females and 8 males) were scanned on a 3T clinical scanner at body and room temperatures to perform T1, T2*, inversion recovery UTE (IR-UTE) T2* measurements, and two-pool magnetization transfer (MT) modeling.
Results
Single-component T2*, IR-T2*, short and long component T2*s from bicomponent analysis, and T1 showed significantly higher values while the noted macromolecular fraction (MMF) from MT modeling showed significantly lower values at body temperature, as compared with room temperature. However, it is noted that the short component fraction (Frac1) showed higher values at body temperature.
Conclusion
This study highlights the need for careful consideration of the temperature effects on MRI measurements, before extending a conclusion from ex vivo studies on cortical bone specimens to clinical in vivo studies. It is noted that the increased relaxation times at higher temperature was most likely due to an increased molecular motion. The T1 increase for the studied human bone specimens was noted as being significantly higher than the previously reported values for bovine cortical bone. The prevailing discipline notes that the increased relaxation times of the bound water likely resulted in a lower signal loss during data acquisition, which led to the incidence of a higher Frac1 at body temperature.
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Fig. 1.
(a) Schematics of the MRI scanning setup which used the regulated temperature air blower (RTAB) to direct warm air at body temperature towards cortical bone specimens in a 30-ml syringe which was placed in a birdcage coil on a 3T clinical scanner. The warm air at 40˚ was directed through a flexible hose towards the transparent bag covering the coil and specimens. (b) Specimens were placed in a 30-ml syringe filled with Fomblin.
Fig. 2.
Ultrashort echo time MR images of fourteen cortical bone specimens in a 30-ml syringe (0.25 mm pixel size) at (a) room temperature and (b) body temperature. Bone specimens were placed in the syringe with three rubber pieces for further comparisons.
Fig. 3.
T2* bicomponent exponential fittings for a representative bone specimen (77-year-old, male, indicated in Fig. 1a) at (a) room temperature and (b) body temperature. T1 single-component exponential fitting for scans at (c) room temperature and (d) body temperature. The two-pool magnetization transfer modeling analyses at (e) room temperature and (f) body temperature using three pulse saturation power levels (400˚ in blue, 600˚ in green, and 800° in red) and five frequency offsets (2, 5, 10, 20, 50 kHz). Macromolecules fraction and macromolecular T2 refer to macromolecular fraction and macromolecular T2, respectively.
Table 1.
Average T2*, T1, and MT Modeling Results at Room Temperature Compared with Body Temperature in Studied Fourteen Cortical Bone Specimens (63 ± 21 years old, 6 females)
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