The investigation of reduced field-of-view diffusion-weighted imaging (DWI) in patients with nasopharyngeal carcinoma: comparison with conventional DWI

Abstract

Background Field-of-view optimized and constrained undistorted single-shot imaging (FOCUS) is a new sequence that shows enhanced anatomical details, improving the diffusion-weighted (DW) images. Purpose To investigate the value of FOCUS diffusion-weighted imaging (DWI) in the evaluation of nasopharyngeal carcinoma (NPC) and compare it with the single-shot echo planner imaging (SS-EPI) DWI approach. Material and Methods A total of 87 patients with NPC underwent magnetic resonance imaging, including FOCUS and SS-EPI DWI sequences. The signal-to-noise ratio (SNR), signal-intensity ratio (SIR), contrast-to-noise ratio (CNR), and apparent diffusion coefficient (ADC) values of the nasopharyngeal lesions were measured and compared. According to the clinical stages of patients, T and N were divided into early and advanced stage groups, respectively. The mean ADC values of the two techniques were computed, and the area under the curve (AUC) was estimated to calculate the diagnostic efficiency. Results Subjective and objective image qualitative values of FOCUS were significantly higher than those of SS-EPI. The ADC values for FOCUS of early T and N stages were significantly lower than those of the advanced stages. Conclusion FOCUS provides significantly better image quality in NPC compared to SS-EPI, with lower ADC values for early-stage disease than late-stage disease.

Comparison of reduced field-of-view DWI and conventional DWI techniques for the assessment of lumbar bone marrow infiltration in patients with acute leukemia

“…In our study, the ADC values from r-FOV DWI were higher than those from conventional DWI, which is accordant with some prior studies ( 24 – 26 ). r-FOV DWI has better spatial resolution, desired fat suppression effects, and less artifacts, so its ADC values may be more accurate.…”

“…Our results suggested the overall image quality was improved on r-FOV DWI with sharper anatomical structure, reduced distortions and artifacts, and higher CNR as well as SIR when compared with conventional DWI. Similar findings were found in previous studies where the r-FOV DWI technique was used to the gallbladder carcinoma (21), cervical carcinoma (22,23), nasopharyngeal carcinoma (26), pancreas lesions (27) and rectal carcinoma (29). By reducing the FOV in the phase-encoding direction, r-FOV DWI has a faster traverse of k-space and a higher bandwidth, which enables it to achieve a higher spatial resolution in the same scan time and decrease image artifacts such as blurring and pixel misregistration (18)(19)(20).…”

“…The SNR of the r-FOV would degrade unless the acquisition time was prolonged, as observed in gallbladder carcinoma ( 21 ), cervical carcinoma ( 22 ), and endometrial cancer ( 24 ). It has also been found in some studies that the SNR of r-FOV is significantly higher or comparable to conventional sequences ( 23 , 25 , 26 ), mainly because the SNR is a relative measurement that is determined by various factors, such as FOV, matrix, echo time, signal average, b-values, magnetic field strength, and T 2 value for the tissue ( 23 , 35 ). Consequently, it is crucial to consider the balance between SNR and spatial resolution as well as acquisition time when setting the scanning parameters to achieve the satisfactory imaging quality.…”

“…However, some studies reported that the ADC values of r-FOV DWI did not differ statistically ( 19 – 22 , 29 ), while others reported significantly lower values than conventional DWI ( 23 , 28 , 30 ). The discrepancy could be explained by the differences in magnetic field strength, imaging technology vendor, b values, echo time, and organs under analysis in the various studies ( 26 , 28 ).…”

“…In the b = 0 s/mm 2 midsagittal images of the two DWI sequences, rectangular regions of interest (ROIs) of about 300mm 2 were placed at the center areas of vertebral cancellous bone from L2 to L4, and ROIs of about 50mm 2 were placed at the background and the L1/2 disc respectively. The ROIs were copied to b = 800 s/mm 2 images automatically, and the signal intensity were recorded ( 26 ). SNR, contrast-to-noise ratio (CNR) and signal intensity ratio (SIR) were calculated based on the following formulas ( 22 , 35 ):…”