No pulsed radio emission during a bursting phase of a Galactic magnetar.

Fast radio bursts (FRBs) are millisecond-duration radio transients of unknown physical origin observed at extragalactic distances1-3. It has long been speculated that magnetars are the engine powering repeating bursts from FRB sources4-13, but no convincing evidence has been collected so far14. Recently, the Galactic magnetar SRG 1935+2154 entered an active phase by emitting intense soft γ-ray bursts15. One FRB-like event with two peaks (FRB 200428) and a luminosity slightly lower than the faintest extragalactic FRBs was detected from the source, in association with a soft γ-ray/hard-X-ray flare18-21. Here we report an eight-hour targeted radio observational campaign comprising four sessions and assisted by multi-wavelength (optical and hard-X-ray) data. During the third session, 29 soft-γ-ray repeater (SGR) bursts were detected in γ-ray energies. Throughout the observing period, we detected no single dispersed pulsed emission coincident with the arrivals of SGR bursts, but unfortunately we were not observing when the FRB was detected. The non-detection places a fluence upper limit that is eight orders of magnitude lower than the fluence of FRB 200428. Our results suggest that FRB-SGR burst associations are rare. FRBs may be highly relativistic and geometrically beamed, or FRB-like events associated with SGR bursts may have narrow spectra and characteristic frequencies outside the observed band. It is also possible that the physical conditions required to achieve coherent radiation in SGR bursts are difficult to satisfy, and that only under extreme conditions could an FRB be associated with an SGR burst.

[Diagnostic accuracy of cone beam computed tomography with different resolution settings for external root resorption].

OBJECTIVE: To evaluate the diagnostic accuracy of cone beam computed tomography (CBCT) with different resolution settings in detecting the simulated external root resorption defects. METHODS: External root resorption defects were simulated in 51 human single rooted premolar teeth. Cavities simulating root resorption defects of 1 mm in diameter and 0.1 mm, 0.2 mm, and 0.3 mm in depth were drilled in the cervical, middle and apical thirds of lingual surfaces of the teeth. In addition to the 51 locations as controls, a total of 102 cavities were obtained in the present study. Specimens were placed in a human dry mandible and scanned by ProMax 3D and DCT PRO CBCT with different resolution settings, respectively. The three-dimensional CBCT images were evaluated by two experienced observers. The data were analyzed with receiver operating characteristics (ROC) analysis. ROC curves were generated and the area under ROC curve (Az) was employed to express the diagnostic accuracy. RESULTS: The diagnostic accuracy (Az value) of ProMax 3D CBCT with high, normal and low resolution settings were 0.867, 0.703 and 0.665 (P < 0.05), respectively. Defects with depths of 0.2 mm and 0.3 mm were easier to be detected than those with depths of 0.1 mm (P < 0.05). The images obtained by high resolution mode scanning had obvious advantages in detecting smaller defects (depth 0.1 mm and 0.2 mm). The DCT PRO CBCT provided 4 resolution settings including normal quality + normal resolution, normal quality + high resolution, high quality + normal resolution and high quality + high resolution. The Az values for those 4 resolution settings were 0.527, 0.725, 0.743, and 0.794 (P < 0.05), respectively. Similar to ProMax 3D CBCT, the scanning mode with high resolution played a better role in detecting the defects with depth of 0.1 mm. Except for the scanning setting mode with normal quality + normal resolution, the other three modes could well be evaluated for the defects with depth of 0.2 mm and 0.3 mm. CONCLUSION: It is concluded that the diagnostic ability for external root resorption of CBCT could be affected by resolution settings. Computer-aid imaging method can improve the CBCT diagnostic accuracy for external root resorption without increasing the radiation dose level during CBCT scanning.

[Dosimetry of cone-beam computed tomography and multi-slice computed tomography scanning for temporal bone].

Objective: To compare the effective radiation dose levels of cone-beam computed tomography (CBCT) with those of multi-slice computed tomography (MSCT) when scanning for the temporal bone. Methods: The absorbed doses of CBCT and MSCT scanners were detected using thermoluminescent dosimeters (TLDs) that were placed in a head and neck phantom and a RGD-3D dose reader.Then the effective doses were calculated and expressed according to the International Commission on Radiation Protection (ICRP) 2007 guidelines. Results: Three-dimensional images about temporal bone can obtained by both CBCT and MSCT scanners in this study.The effective dose value of CBCT scanning for bilateral and unilateral temporal bone was 164.1 µSv (bone marrow: 32.1 µSv; thyroid gland: 10.6 µSv; salivary glands: 31.0 µSv), and 98.1 µSv (bone marrow: 17.4 µSv; thyroid gland: 6.2 µSv; salivary glands: 16.1 µSv), respectively.The dose of MSCT scanning for bilateral temporal bone was 714.6 µSv (bone marrow: 95.1 µSv; thyroid gland: 127.8 µSv; salivary glands: 135.7 µSv). Conclusions: When scanning for the temporal regions, the dose levels for CBCT are lower than those for MSCT.Dose levels reduction for CBCT could be obtained when smaller regions were scanned.