A study of the diagnostic efficacy of diffusion-weighted magnetic resonance imaging in the diagnosis of perianal fistula and its complications

Purpose: To determine the diagnostic efficacy of diffusion-weighted magnetic resonance imaging (DWI) in the diagnosis of perianal fistula and its complications. Material and methods: This is a retrospective study based on the data of 47 patients with a clinical diagnosis of perianal fistula, who had an MRI study performed on a 1.5-T GE Signa MR scanner. DWI sequences were done using 3 different b-values. Other routine MR sequences were included. The MR images were studied to compare the diagnostic efficacy of the DW MRI sequence and other sequences in diagnosing perianal fistula and its complications. Apparent diffusion coefficient (ADC) values of abscesses and inflammatory soft tissue lesions were measured using ADC maps. The standard reference to obtain diagnostic efficacy was post-surgical data. Results: Seventy-nine perianal fistulas were diagnosed in 47 patients who had undergone an MRI study. The sensitivity and specificity of different MR sequences in diagnosing perianal fistulas are T2 FSFSE: 92% sensitivity; DWI: 96% sensitivity; combined T2+DWI: 100% sensitivity; and post-gadolinium T1 FS has 100% sensitivity in diagnosing perianal fistulas. The mean apparent diffusion coefficient for the abscess in our study was 0.990 ± 0.05 × 10-3, and the mean apparent diffusion coefficient for an inflammatory soft tissue lesion was 1.440 ± 0.05 × 10-3. The optimal ADC cut-off for the abscess was 1.098 × 10-3 mm2/s showing 100% sensitivity and 93.8% specificity. Conclusions: DW imaging is a reliable sequence to diagnose perianal fistula and its complications. Measurement of ADC values is reliable in diagnosing perianal abscess collection. DWI sequence helps patients with renal impairment in whom IV gadolinium is contraindicated

Diurnal and seasonal variability of turbulence parameters observed with Indian mesosphere-stratosphere-troposphere radar

Seasonal and diurnal variation of turbulence parameters such as refractivity structure constant Cn2 and eddy dissipation rate ε is presented using the data collected with the Indian mesosphere-stratosphere-troposphere (MST) radar over 3 years. The log Cn2 values estimated from signal-to-noise ratio (SNR) are found to be in the range of -17 to -19 m-2/3 in the height range of 7.5-21 km. Monthly mean values of log Cn2 show a maximum variation below 12 km with a magnitude of 12-15 dB during the course of annual cycle. A maximum variability of ~7-10 dB is observed below 12 km in seasonal mean values of log Cn2. The diurnal variation of log Cn2 at different heights is also given. Cn2 is found to be more in the region of strong shears, generally observed in the boundaries of jet streams. Different methods for the estimation of eddy dissipation rate and their limitations are discussed. For the present study, spectral width method is used after correcting the observed spectral width from beam and shear broadening effects. The observed median log ε is on the order of -3 to -4 m2 s-3. Monthly variation of log ε is found to be ~5-7 dB. Below 10 km the magnitude of ε is more in the postmonsoon than that observed in other seasons. The interannual variation of ε is less in winter than in other seasons. The diurnal variation of log ε is found to be small in postmonsoon at most of the heights. To facilitate a comparison with the other results, we have estimated the eddy diffusivity K and the inner and outer scales of turbulence. The observed values of Cn2, ε, K, and the inner and outer scales of turbulence are largely consistent with the results available in the literature