Selection and application of coils in temporomandibular joint MRI.

OBJECTIVE: To compare and evaluate the signal-to-noise ratio (SNR) and the contrast-to-noise ratio (CNR) values between a 15-channel phased array head coil and 6-channel dS Flex M surface coil in the MRI of temporomandibular joint. METHODS: 300 patients were randomly assigned to two groups: 150 patients were examined by using a 15-channel phased array head coil and the other 150 patients were scanned by using a 6-channel dS Flex M surface coil. All of the data were set in the same 6 regions of interest including the temporal lobe, condyle neck, lateral pterygoid muscle, parotid gland, the adipose area and an area of the background noise）. SNR and CNR values were measured respectively. RESULTS: The numerical variation law of SNR and CNR values measured in regionsof interest of each group was similar, although different coils were used. There were statistically significant differences of SNR values in all of the oblique sagittal (OSag) proton density-weighted imaging, the part of OSag T 2 weighted image (T 2WI) except for SNR4 and SNR5. and oblique coronal (OCor) T 2WI sequence except for SNR2. On the contrary, SNR4 and SNR5 values in the OCor T 2WI and SNR5 values in OSag T 2WI sequences by using the surface coil were higher than those by using the head coil. There were no statistically significant intergroup differences of CNR values in OSag proton density-weighted imaging sequence except CNR1 and in OSag T 2WI sequence except CNR5. But, statistically significant differences of all the values in the OCor T 2WI sequence except for CNR1 were observed. CONCLUSION: Both the phased array head coil and dS Flex M surface coil can be used for temporomandibular joint MRI.

[Clinical analysis of spectrum CT imaging reducing metal artifacts of oral and maxillofacial region].

PURPOSE: To assess the capability of monochromatic energy images of gemstone spectral imaging(GSI) by using spectral CT in reducing metal artifacts of oral and maxillofacial region. METHODS: Spectral CT imaging was applied to 46 patients with metallic implants with GSI sequence to measure CT numbers (expressed in Hounsfield units, HU) and SD (standard deviation) numbers of the soft tissues. 11 monochromatic-image groups were obtained, ranging from 40 keV(kiloelectronvolts) to 140 keV (every 10 keV as one group). The data were analyzed with SPSS19.0 software package. RESULTS: Images in 20 subjects with orthodontic appliance, the minimal average AI ranged between (23.86±10.90) to (24.42±11.54) HU. Similarly, in 12 subjects with titanium implants, the minimal average AI ranged between (26.49±9.40) to (26.95±8.97) HU. In 10 images from 14 subjects with dental fillings or fixed dentures, the minimal average AI ranged between (29.84±13.04) to (30.97±13.15) HU. The average AI values were (63.36±70.52), (70.82±105.14) and (107.35±147.57) HU from 40 keV to 140 keV in 3 groups, respectively, which was similar to the average AI values of 70keV monochromatic images (61.46±32.06, 70.18±62.86, 110.28±78.70) HU in each corresponding group. There was a significant difference about AI value among 3 energy spectrum groups (P<0.05). CONCLUSIONS：Spectral CT imaging could obviously reduce metal artifacts, and improve the display capabilities of the structures around the metallic implants. 70 keV is the dividing point of metal artifact subtraction. The optimal energy range is at 110-140 keV in reducing metal artifacts of oral and maxillofacial region.