Zoomed echo-planar imaging using parallel transmission: impact on image quality of diffusion-weighted imaging of the prostate at 3T.

PURPOSE: To assess impact of two-channel parallel transmission (pTx) with focused excitation [zoomed echo-planar imaging (EPI)] on image quality of prostate diffusion-weighted imaging (DWI) at 3T. METHODS: 27 male volunteers (27 ± 8 years) underwent 3T prostate MRI using 2-channel radiofrequency-transmit system and 18-channel torso receive coil. Scans included EPI-DWI sequence (b values 50, 500, 1000 s/mm(2)) acquired both with standard sinc pulse and 2-channel pTX with focused excitation, each acquired at large-field-of-view (FOV) (20 × 20 cm) and small-FOV (14 × 14 cm). An abdominal radiologist scored b-1000 images and ADC maps for image quality measures. Sequences were compared using paired Wilcoxon tests. RESULTS: pTx with focused excitation showed significant improvements compared with standard DWI on b-1000 images at large-FOV for the absence of wrap and overall image quality (p ≤ 0.049); on b-1000 images at small-FOV for reduced distortion of prostate, absence of ghosting, absence of wrap, clarity of prostate capsule, clarity of peripheral/transition zone boundary, clarity of peri-urethral region, and overall image quality (p ≤ 0.004); and on ADC maps at small-FOV for reduced distortion of prostate, sharpness of prostate, clarity of prostatic capsule, clarity of peri-urethral region, and overall image quality (p = 0.002-0.036). When compared with standard large-FOV images, small-FOV images obtained using pTx with focused excitation showed no significant difference on the b-1000 images for any feature (p ≥ 0.175), while showing significant improvements on the ADC maps in terms of reduced distortion, absence of ghosting, and absence of wrap (p = 0.010-0.030). CONCLUSION: Zoomed DWI using 2-channel pTx reduced artifacts and improved image quality for 3T prostate DWI; benefit was most apparent for small-FOV images.

Evaluation of radiation dose among patients admitted through a university hospital emergency department.

This study was conducted to evaluate the impact of different patient presentations/characteristics on medical imaging and radiation exposure. We collected data on the estimated effective radiation dose (EED) of patients admitted through our University Hospital ER, and analyzed the relationships of patient gender, age, admitting diagnosis, and admission duration on EED. All (592) patients admitted through our ER (with imaging) during 1-week periods in May/November 2009 were included. To compare EEDs according to admission diagnosis, seven categories were created: Cardiopulmonary, Gastrointestinal, Genitourinary, Neurologic, Trauma, Infectious, and Other. EEDs of patients with various admission durations were also evaluated. Units for all EEDs are mSv. Median EED (MEED) for all patients was 4.5. Males (7.8, females = 2.5) and adults (6.1, pediatrics = 1.8) experienced higher MEEDs, but significance was lost after controlling for other variables. MEED increased with admission duration (0.1 for <24 h, 1.8 for 1-3 days and 92.0 for >2 months). Trauma patients experienced the highest MEED (18.3), while patients with gastrointestinal/genitourinary diagnoses experienced the second highest MEED (13.0 mSv for both). Pediatric/male patients experienced heightened radiation exposure, but these relationships were largely due to other variables (higher male frequency/severity of trauma, pediatric patients had shorter admissions and diagnoses requiring less radiologic workup). Patients admitted following trauma and for prolonged durations showed elevated radiation exposure even after adjustment for all other variables. The identification of these relationships may aid in the development and focusing of future radiation awareness/reduction efforts to persons involved in the evaluation and care of patients with these presentations and characteristics.