الفهرس 
INTRODUCTION & REVIEW OF LITERATUREOnly 14 pages are availabe for public view
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Abstract
DWMRI is an emerging non-invasive functional MRI technique that expresses freedom of motion of water molecules in intercellular spaces and relates to cellular density of tissues. Free water molecules normally contribute to signal formation in MRI. Biological barriers, principally cell membranes impair the free displacement of water molecules thus resulting in restricted diffusivity. Restricted diffusivity is seen in a variety of conditions including tumors with increased cellularity, infection and inflammation, as well as very thick fluids (abscesses) but in clear fluids (cysts) no motion restriction is observed. (59), (60)
This study included a total of seventeen (17) patients, ten (10) males and seven (7) females (age range: 13-68 years) selected from the outpatients’ clinic of Oral Surgery Department, Faculty of Dentistry, Ain-shams University. MRI examination was carried out in Oral Radiology Department, Faculty of Medicine, Ain-shams University with the following MRI Machine specifications: Philips 1.5 Tesla Achieva, Netherlands with multi-transmit, receive capabilities and 3 coils (ds base, ds head neck, ds posterior). T1 sequence parameters: repetition time (TR)/echo time (TE), 544/14ms, field of view of 260×207×134, Reconstruction matrix size: 672, section thickness: 4 mm, slice gap: 0.8 mm. T2 sequence parameters: TR/TE,3163/100ms, field of view of 253×200×129, Reconstruction matrix size: 512, section thickness: 4 mm, slice gap: 1 mm. DWMRI sequence parameters: TR/TE, 3730/64ms, field of view of 235 ×235×221 mm, Reconstruction matrix size: 320, section thickness: 5mm, slice gap: 0.4 mm, diffusion gradient encoding in three (x, y, z) orthogonal directions, b values of 0 and 800 s/mm2.
Malignant lesions appear restricted due to strong restriction of the movement of water molecules as result of the increase in cell density in the tumor matrix and increase in cell membranes. However, non-malignant lesions appear mainly facilitated due to free diffusion of water molecules as result of the decrease in cellularity and restrictive cell membranes.
The current study showed that there was a statistically significant difference between T1 signal distributions among patients with benign and malignant lesions (P-value= 0.027, Effect size= 0.685), Benign lesions showed higher prevalence of low signal while malignant lesions showed higher prevalence of intermediate signal. There was a statistically significant difference between T2 signal distributions among patients with benign and malignant lesions (P-value= 0.029, Effect size= 0.609), Benign lesions showed higher prevalence of high signal while malignant lesions showed higher prevalence of intermediate signal.
The present study showed that the mean ADC value for benign lesions (1.646 ± 0.305 ×10−3 mm2 /s) was significantly higher than that in malignant lesions (0.758 ± 0.153 ×10−3 mm2 /s; p < 0.001). ROC analysis revealed an optimal threshold value for the differentiation between malignant and benign lesions with an ADC cut-off value (≤ 1 10-3 mm2 with diagnostic accuracy of 94.1%, a sensitivity of 100% and specificity of 91.7%) indicating that ADC values less than or equal to 1 10-3 mm2 indicate malignant lesions and values greater than 1 10-3 mm2 indicate benign lesions.
Our study showed that there are some exceptions such as odontogenic keratocyst that showed restricted diffusion compared to the other cysts due to the presence of keratin which increase the viscosity of the contents of OKC.
This study concluded that DWMRI is highly accurate in the differentiation between benign and malignant intraosseous lesions of the jaws.