Impact of noise reduction on radiation dose reduction potential of virtual monochromatic spectral images: Comparison of phantom images with conventional 120 kVp images using deep learning image reconstruction and hybrid iterative reconstruction.

PURPOSE: To assess the effects of deep learning image reconstruction (DLIR) and hybrid iterative reconstruction (HIR) on the image quality of virtual monochromatic spectral (VMS) images and to investigate the dose reduction potential of the VMS and conventional 120 kVp images. METHODS: A cylindrical phantom simulating an adult abdomen was used. The contrast was set to 60 (medium) and 300 (high) Hounsfield units. CT acquisitions were performed at three dose levels: 12, 9, and 6 mGy. Images were reconstructed via filtered back projection (FBP), DLIR, and HIR. The noise power spectrum (NPS) and task transfer function (TTF) were measured, and the system performance (SP) function was calculated (TTF2/NPS). RESULTS: The noise magnitudes at low spatial frequencies with DLIR and HIR were lower than that with FBP by 45.6% and 24.4%, respectively. Compared to the FBP results, the TTF values at 50% with DLIR at medium and high contrast changed by -13.2% and +25.3% with the VMS images and -2.0% and +9.3% with the 120 kVp images, respectively. In the VMS and 120 kVp images, compared to the SP values of 12 mGy FBP images, SP values of 6 mGy DLIR images decreased at medium contrast and increased at high contrast. CONCLUSIONS: DLIR achieved better noise reduction than HIR. The spatial resolution of VMS-DLIR varied significantly depending on the contrast. The image quality of VMS-DLIR and 120 kVp-DLIR potentially decrease in medium contrast tasks and increase in high contrast tasks with 50% dose reduction.

Assessment of the image quality of virtual monochromatic spectral computed tomography images: a phantom study considering object contrast, radiation dose, and frequency characteristics.

Fast kilovoltage (kVp)-switching technology cannot obtain conventional 120 kVp images; thus, 70 keV virtual monochromatic spectral computed tomography (CT) images (VMSI) are generally used. The contrast-to-noise ratio (CNR) is used to evaluate the image quality of VMSI; however, CNR does not include frequency characteristics. The present study aimed to investigate the evaluation methods of VMSI considering frequency characteristics by comparing the image quality of 70 keV VMSI with that of conventional 120 kVp images. The evaluated object contrasts were 70 and 300 Hounsfield units (HU). Scans used two radiation dose levels: low (LD) and standard (SD). The volume CT dose index of LD and SD was 4.8- and 12 mGy, respectively. Images were reconstructed by filtered back projection, evaluating CNR, noise power spectrum (NPS), task transfer function (TTF), and system performance (SP) function calculated as TTF2/ NPS. The total NPS values (spatial frequency range: 0.2 ~ 0.4 mm-1) of 70 keV VMSI were higher than those of 120 kVp images. The spatial frequency TTF values that reached 10% (f10%) of the 70 keV VMSI changed based on object contrast. For the low-contrast condition, a lower f10% was observed with 70 keV VMSI. The CNR of 70 keV VMSI was comparable to that of 120 kVp images in low- and high-contrast conditions. However, for 70 keV VMSI, SP of low-contrast was low, and SP of high-contrast was high, compared with those of 120 kVp images. This study suggested that only CNR was not sufficient to evaluate the image quality of VMSI; thus, evaluation methods considering frequency characteristics should be used.

[Evaluation of Low-contrast Detectability of Iterative Reconstruction Algorithm in High-speed CT Technology for Head].

PURPOSE: The purpose of this study was to assess the feasibility of high-speed CT technology for head without deterioration of low-contrast detectability using the brain LCD (Canon Medical Systems) of iterative reconstruction. METHODS: System performance (SP) function analysis, low-contrast object specific contrast-to-noise ratio (CNRLO) analysis, and visual evaluation using Scheffe's paired comparison were performed. Additionally, analysis of the correlation of CNRLO and visual scores was performed. SP was performed with the self-made phantom. CNRLO was calculated with the catphan 504 phantom (CTP 515). Visual evaluation was performed using the brain phantom which simulated such as cerebral infarction and investigated on a fivepoint scale. All images were acquired with pitch factor of 0.61 (low pitch) and 1.40 (high pitch). All images were reconstructed with filtered back projection (FBP), brain LCD standard (LCD STD) and strong (LCD STR). RESULTS: SP of brain LCD improved compared with FBP. CNRLO of FBP decreased in high pitch compared with low pitch. CNRLO of brain LCD images acquired by low- and high pitch were improved compared with FBP. Visual scores denoted similar trends to that of CNRLO and there was high correlation with CNRLO. CONCLUSION: It was suggested that using brain LCD can achieve the high speed CT technology for head without deterioration of low-contrast detectability.

Image quality of virtual monochromatic images obtained using 320-detector row CT: A phantom study evaluating the effects of iterative reconstruction and body size.

OBJECTIVES: To compare the image quality between virtual monochromatic spectral (VMS) images obtained using 320-row detector CT and polychromatic 120-kVp images reconstructed with or without iterative reconstruction using various phantom sizes. MATERIALS AND METHODS: Torso phantoms simulating three patient sizes and containing four syringes filled with water or different contrast media (5, 10, 15mgI/mL15mgI/ml) were used. The phantoms were scanned using dual-energy (80/135-kVp) and single-energy (120-kVp) protocols at different settings (20mGy, 12mGy, and 6mGy). VMS images were generated at 1-keV intervals (range, 35-135keV). Both the VMS images and the single-energy 120-kVp images were reconstructed using filtered back projection (FBP) and adaptive iterative dose reduction 3D (AIDR-3D). The signal-to-noise ratio (SNR), and the contrast-to-noise ratio (CNR) were assessed. RESULTS: Using FBP reconstruction, the SNR and CNR of the VMS images were lower than or similar to those of the 120-kVp images for most dose settings. Using AIDR-3D reconstruction, however, the 70-keV VMS images had higher SNRs and CNRs than the 120-kVp images at most settings. CONCLUSIONS: The image quality of VMS images with FBP reconstruction tended to be lower than that of the 120-kVp images. With the use of AIDR-3D, however, approximately 70-keV VMS images had a higher image quality than the 120-kVp images.

Clinical experience of bone anchored hearing aid: a case report.

To improve conventional bone conduction hearing aids, Tjellstrom, Branemark, developed an implant system consisting of a maxillofacial implant that derived from dental implants and a bone conduction hearing aid that was attached directly to the implant. This system has been commercially available as a bone anchored hearing aid (BAHA). More than 10,000 patients have benefited from BAHA in Scandinavia, North America, and many other regions. BAHA first became available in 1977 in Sweden but has not been used in Japan as widely as expected. This paper reports a case of a 8-year use of BAHA for hearing loss caused by microtia and external auditory canal atresia, with a review of literature. The patient has been followed up for 9 years after implant placement. Play audiometry with a loudspeaker showed a hearing loss of 25 dB. The patient says that BAHA is superior to conventional transcutaneous bone conduction hearing aids in easiness of attachment, esthetics, and speech recognition and music recognition. The skin and the bone around the implants remain in favorable condition. She has been free from the use of a headband for a conventional hearing aid.

A new device for fixing the premaxilla with osteotomy in a child with complete bilateral cleft lip and palate in the mixed dentition period--a preliminary case report.

In the treatment of a protruded premaxilla associated with complete bilateral cleft lip and palate, some patients require surgical setback of the premaxilla with osteotomy as functional and aesthetic treatment. No satisfactory surgical approaches have been established for the setback because it is usually difficult to fix the premaxilla after osteotomy in the mixed dentition period. This paper reports the new method for fixing the premaxilla with osteotomy in a child with a severely protruded premaxilla in the mixed dentition period. To fix the segment, we fabricated a device consisting of a palatal bite plate and an anterior tray before surgery. The space between the tray and the premaxilla was filled with soft resin during surgery so that the reposition of the premaxilla could be adjusted. This approach produced a favorable result. Our device has several advantages. It allows the adjustment of repositioning of the premaxilla during surgery. It can change the range of the adjustment according to the intended position of the premaxilla. It allows secure fixation of the segment. It is removable for tooth brushing and observation of bone union. Our device can be applied to many children similar to our patient reported in this paper.

A case of chronic infection 28 years after silicone orbital implant.

Silicone was one of the most common biocompatible materials used for orbital floor reconstruction about twenty to thirty years ago. Recently, surgeons hardly use silicone due to numerous reports of complications such as infection, extrusion and implant displacement. We present a case of chronic infection seen after 28 years of silicone implant used in orbital floor repair. Although it is reported that infection due to silicone implant may decrease after long years of follow up, our case demonstrated the possible case of unexpected infection after more than twenty years with orbital silicone implant.

Salvage operations of free tissue transfer following internal jugular venous thrombosis: a review of 4 cases.

The internal jugular vein (IJV) is used as the optimal recipient for free-tissue transfer in reconstruction following modified radical neck dissection. Some reports documented rare cases of flap compromise following IJV thrombosis, but large sample studies are few. We present cases of emergent exploration and an analysis of factors to improve salvage rates of compromise due to IJV thrombosis. From a survey of 756 patients, four developed congestion due to IJV thrombosis and returned to the operating room. A restrospective analysis was made from the case records. This represents a rate of 0.5% for the entire series. Three flaps survived,and one failed. Detection of compromise ranged from 7-25 h postoperatively. All four IJVs recovered to provide adequate drainage after thrombectomy. While flap compromise following IJV thrombosis is rare, careful observation and early exploration are crucial for salvage, as in other microvascular venous crises.