Gumbel distribution-based technique enables quantitative comparison between streak metal artifacts of multidetector row CT and cone-beam CT: a phantom study.

Cone-beam computed tomography (CBCT), derived from multidetector row CT (MDCT), has a high spatial resolution and has recently been applied to various organs. One of the severe limitations common to CBCT and MDCT is metal artifacts. In particular, streak metal artifacts (SMAs) between multiple metal materials often hinder diagnosis. However, no studies have quantitatively compared the strength of SMAs in MDCT and CBCT. Nomura et al. reported an evaluation method specialized in SMAs of CBCT using the Gumbel distribution (GD), which can also be applied to SMAs of MDCT (Oral Surg Oral Med Oral Pathol Oral Radiol 131: 494-502, 2021, https://doi.org/10.1016/J.OOOO.2020.08.031 ). This study aimed to quantitatively compare SMAs occurring between titanium materials on MDCT and CBCT images using the GD-based method. The SMAs were investigated as follows: A hydroxyapatite block was sandwiched between two titanium rods to generate an SMA. They were placed in an acrylic phantom, simulating a human head, and scanned using an MDCT scanner and two CBCT scanners. The obtained images were analyzed using Gumbel plots and location parameters, and the SMA strength was calculated. The results showed that the SMAs on the MDCT images were significantly weaker than those on the CBCT images. In the CBCT scans, a smaller volume CT dose index value caused stronger SMAs. These results indicate that MDCT is more advantageous than CBCT in terms of SMA reduction when bone morphology between titanium materials must be evaluated. The characteristic should be considered in clinical cases.

Turning and multitask gait unmask gait disturbance in mild-to-moderate multiple sclerosis: Underlying specific cortical thinning and connecting fibers damage.

Multiple sclerosis (MS) causes gait and cognitive impairments that are partially normalized by compensatory mechanisms. We aimed to identify the gait tasks that unmask gait disturbance and the underlying neural correlates in MS. We included 25 patients with MS (Expanded Disability Status Scale score: median 2.0, interquartile range 1.0-2.5) and 19 healthy controls. Fast-paced gait examinations with inertial measurement units were conducted, including straight or circular walking with or without cognitive/motor tasks, and the timed up and go test (TUG). Receiver operating characteristic curve analysis was performed to distinguish both groups by the gait parameters. The correlation between gait parameters and cortical thickness or fractional anisotropy values was examined by using three-dimensional T1-weighted imaging and diffusion tensor imaging, respectively (corrected p < .05). Total TUG duration (>6.0 s, sensitivity 88.0%, specificity 84.2%) and stride velocity during cognitive dual-task circular walking (<1.12 m/s, 84.0%, 84.2%) had the highest discriminative power of the two groups. Deterioration of these gait parameters was correlated with thinner cortical thickness in regional areas, including the left precuneus and left temporoparietal junction, overlapped with parts of the default mode network, ventral attention network, and frontoparietal network. Total TUG duration was negatively correlated with fractional anisotropy values in the deep cerebral white matter areas. Turning and multitask gait may be optimal to unveil partially compensated gait disturbance in patients with mild-to-moderate MS through dynamic balance control and multitask processing, based on the structural damage in functional networks.

Magnetic resonance imaging of methotrexate-related lymphoproliferative disorder with a chief complaint of oral symptoms.

OBJECTIVES: To determine the magnetic resonance imaging (MRI) features of methotrexate-related lymphoproliferative disorder (MTX-LPD) in the oral cavity of a patient with a chief complaint of oral symptoms. METHODS: We included six patients who visited our hospital between November 2014 and November 2019, histopathologically diagnosed with MTX-LPD. All images were examined using 3 T MRI and reviewed by two radiologists. RESULTS: Masses were detected in five cases; all masses demonstrated signal hypointensity and homogeneous signal hyperintensity on T1- and T2-weighted images with fat suppression. Homogeneous enhancement with fat suppression was evident on post-contrast T1-weighted imaging. We performed dynamic contrast-enhanced MRI in three cases and observed early enhancement with a low washout ratio pattern in all cases. Four patients underwent diffusion-weighted MRI and revealed low mean apparent diffusion coefficient (ADC) of 0.57 (range 0.5-0.65) × 10-3 mm2/s. CONCLUSIONS: We reported on the imaging characteristics of six rare cases of MTX-LPD in the oral cavity. Homogeneous hyperintensity on fat-suppressed T2-weighted images and low ADC values are possible features of MTX-LPD. Moreover, MTX-LPD can be differentiated from other carcinomas in the oral cavity.

Differentiation of cystic lesions in the jaw by conventional magnetic resonance imaging and diffusion-weighted imaging.

OBJECTIVES: This study aimed to determine the discrimination power of apparent diffusion coefficient (ADC) for cystic lesions in the jaw using MRI. METHODS: We selected 127 cystic lesions, comprising dentigerous cysts (DCs), odontogenic keratocysts (OKCs), and unicystic ameloblastomas (UABs), from our MRI database examined by 3T MRI, including diffusion-weighted imaging sequences, and we reviewed their imaging characteristics. We attempted to discriminate the three types of lesions by ADC values with receiver operator characteristic analysis; however, satisfactory results were not obtained for differentiation between DC and OKC. Therefore, we performed a decision tree analysis. RESULTS: The imaging characteristics of the lesions were significantly different according to Fisher's exact test, except for differences in sex. The ADC values statistically discriminated the lesions of DC and UAB, OKC and UAB, but not DC and OKC. Thus, differentiation was performed by a decision tree for DC and OKC by evaluating the following points: the attached tooth condition, signal intensity on the T1 weighted image (T1SI), ADC value, and the cyst site. However, cases showing hypo- or isointense T1SI with an ADC value under 1.168 × 10-3 mm2/s were difficult to differentiate. CONCLUSION: The ADC value helped distinguish UAB from both DC and OKC, but not DC from OKC. However, the decision tree based on ADC value, tooth contact status, and T1SI helped differentiate DC and OKC to some extent.

Quantitative evaluation of artefact reduction from metallic dental materials in short tau inversion recovery imaging: efficacy of syngo WARP at 3.0 tesla.

OBJECTIVES: To evaluate the effects of syngo WARP on reducing metal artefacts from dental materials. METHODS: Short tau inversion recovery (STIR) with syngo WARP [a dedicated metal artefact reduction sequence in combination with view-angle-tilting (VAT)] was performed using phantoms of three dental alloys: cobalt-chromium (Co-Cr), nickel-chromium (Ni-Cr), and titanium (Ti). Artefact volumes and reduction ratios of black, white and overall artefacts in the standard STIR and syngo WARP images with several different parameter settings were quantified according to standards of the American Society for Testing and Materials F2119-07. In all sequences, the artefact volumes and reduction ratios were compared. The modulation transfer function (MTF) and contrast-to-noise ratio (CNR) were also measured for evaluation of image quality. RESULTS: In standard STIR, the overall artefact volume of Co-Cr was markedly larger than those of Ni-Cr and Ti. All types of artefacts tended to be reduced with increasing receiver bandwidth (rBW) and VAT. The effect of artefact reduction tended to be more obvious in the axial plane than in the sagittal plane. Compared with standard STIR, syngo WARP with a matrix of 384 × 384, receiver bandwidth of 620 Hz/pixel, and VAT of 100 % in the axial plane obtained reduction effects of 30 % (white artefacts), 45 % (black artefacts), and 38 % (overall artefacts) although MTF and CNR decreased by 30 and 22 % compared with those of standard STIR, respectively. CONCLUSIONS: syngo WARP for STIR can effectively reduce metal artefacts from dental materials.