1.5 T MRI with a Dedicated Dental Signal-Amplification Coil as Noninvasive, Radiation-Free Alternative to CBCT in Presurgical Implant Planning Procedures

PURPOSE

Cone beam computed tomography (CBCT) is considered both reliable and safe and provides reproducible results in guided dental implant planning procedures. However, it has weaknesses in soft tissue contrast and is associated with radiation exposure. Recent studies showed promising results with magnetic resonance imaging (MRI) as a possible noninvasive, radiation-free, alternative imaging modality for dental indications. The purpose of this study was to evaluate the quality of 1.5 T MRI with a dedicated dental signal-amplification coil in comparison to CBCT for dental implant planning procedures.

MATERIALS AND METHODS

Sixteen subjects undergoing preoperative MRI (3D HR T1w TSE and 3D HR T1w FFE) and CBCT were included in this prospective study. All imaging data were used for dental implant planning procedures using commercially available software. Two experts scored the planning as "ideal," "improvable," or "unacceptable." Furthermore, quantitative distances according to EuCC recommendations were collected. Finally, discrepancies between CBCT and 3D HR T1w TSE were analyzed. Statistical analysis was performed using the Mann-Whitney U test and analysis of variance (ANOVA).

RESULTS

The dental implant planning procedure was technically feasibly using all imaging data. CBCT allowed for "ideal" placement in all cases. Ratings for 3D HR T1w TSE and 3D HR T1w FFE were 81.9%, 18.1%, and 0% and 54.2%, 30.0%, and 15.3% for ideal, improvable, and unacceptable, respectively, identifying 3D HR T1w TSE as superior compared with 3D HR T1w FFE. Head-to-head comparison between CBCT and 3D HR T1w TSE revealed no significant differences regarding the apical position of the implant of 1.2 ± 0.7 mm and 1.3 ± 0.5 mm coronally, respectively (P = .287). The deviation of the planed angle was 3.0 ± 1.2 degrees. In these merged data sets, the distance to the mandibular canal was significantly higher with 1.3 ± 0.8 mm, indicating better utilization of the existing bone.

CONCLUSION

Within the limits of this pilot study, it can be reported that the dental image planning procedure is feasible using 1.5 T MRI with a dedicated dental coil and specific MRI sequences.

Phantomless assessment of volumetric bone mineral density using virtual non-contrast images from spectral detector computed tomography

OBJECTIVE

To evaluate phantomless assessment of volumetric bone mineral density (vBMD) based on virtual non-contrast images of arterial (VNC_a) and venous phase (VNC_v) derived from spectral detector CT in comparison to true non-contrast (TNC) images and adjusted venous phase conventional images (CI_V(adjusted)).

METHODS

104 consecutive patients who underwent triphasic spectral detector CT between January 2018 and April 2019 were retrospectively included. TNC, VNC_a, VNC_v and venous phase images (CI_V) were reconstructed. vBMD was obtained by two radiologists using an FDA/CE-cleared software. Average vBMD of the first three lumbar vertebrae was determined in each reconstruction; vBMD of CI_V was adjusted for contrast enhancement as suggested earlier.

RESULTS

vBMD values obtained from CI_V(adjusted) are comparable to vBMD values derived from TNC images (91.79 ± 36.52 vs 90.16 ± 41.71 mg/cm³, p = 1.00); however, vBMD values derived from VNC_a and VNC_v (42.20 ± 22.50 and 41.98 ± 23.3 mg/cm³ respectively) were significantly lower as compared to vBMD values from TNC and CI_V(adjusted) (all p ≤ 0.01).

CONCLUSION

Spectral detector CT-derived virtual non-contrast images systematically underestimate vBMD and therefore should not be used without appropriate adjustments. Adjusted venous phase images provide reliable results and may be utilized for an opportunistic BMD screening in CT examinations.

ADVANCES IN KNOWLEDGE

Adjustments of venous phase images facilitate opportunistic assessment of vBMD, while spectral detector CT-derived VNC images systematically underestimate vBMD.

Utility of virtual monoenergetic images from spectral detector computed tomography in improving image segmentation for purposes of 3D printing and modeling

BACKGROUND

One of the key steps in generating three-dimensional (3D) printed models in medicine is segmentation of radiologic imaging. The software tools used for segmentation may be automated, semi-automated, or manual which rely on differences in material density, attenuation characteristics, and/or advanced software algorithms. Spectral Detector Computed Tomography (SDCT) is a form of dual energy computed tomography that works at the detector level to generate virtual monoenergetic images (VMI) at different energies/ kilo-electron volts (keV). These VMI have varying contrast and attenuation characteristics relative to material density. The purpose of this pilot project is to explore the use of VMI in segmentation for medical 3D printing in four separate clinical scenarios. Cases were retrospectively selected based on varying complexity, value of spectral data, and across multiple clinical disciplines (Vascular, Cardiology, Oncology, and Orthopedic).

RESULTS

In all four clinical cases presented, the segmentation process was qualitatively reported as easier, faster, and increased the operator's confidence in obtaining accurate anatomy. All cases demonstrated a significant difference in the calculated Hounsfield Units between conventional and VMI data at the level of targeted segmentation anatomy. Two cases would not have been feasible for segmentation and 3D printing using conventional images only. VMI data significantly reduced conventional CT artifacts in one of the cases.

CONCLUSION

Utilization of VMI from SDCT can improve and assist the segmentation of target anatomy for medical 3D printing by enhancing material contrast and decreasing CT artifact.

Thoracic-abdominal imaging with a novel dual-layer spectral detector CT: intra-individual comparison of image quality and radiation dose with 128-row single-energy acquisition

BACKGROUND

A novel, multi-energy, dual-layer spectral detector computed tomography (SDCT) is commercially available now with the vendor's claim that it yields the same or better quality of polychromatic, conventional CT images like modern single-energy CT scanners without any radiation dose penalty.

PURPOSE

To intra-individually compare the quality of conventional polychromatic CT images acquired with a dual-layer spectral detector (SDCT) and the latest generation 128-row single-energy-detector (CT128) from the same manufacturer.

MATERIAL AND METHODS

Fifty patients underwent portal-venous phase, thoracic-abdominal CT scans with the SDCT and prior CT128 imaging. The SDCT scanning protocol was adapted to yield a similar estimated dose length product (DLP) as the CT128. Patient dose optimization by automatic tube current modulation and CT image reconstruction with a state-of-the-art iterative algorithm were identical on both scanners. CT image contrast-to-noise ratio (CNR) was compared between the SDCT and CT128 in different anatomic structures. Image quality and noise were assessed independently by two readers with 5-point-Likert-scales. Volume CT dose index (CTDI_vol), and DLP were recorded and normalized to 68 cm acquisition length (DLP₆₈).

RESULTS

The SDCT yielded higher mean CNR values of 30.0% ± 2.0% (26.4-32.5%) in all anatomic structures ( P < 0.001) and excellent scores for qualitative parameters surpassing the CT128 (all P < 0.0001) with substantial inter-rater agreement (κ ≥ 0.801). Despite adapted scan protocols the SDCT yielded lower values for CTDI_vol (-10.1 ± 12.8%), DLP (-13.1 ± 13.9%), and DLP₆₈ (-15.3 ± 16.9%) than the CT128 (all P < 0.0001).

CONCLUSION

The SDCT scanner yielded better CT image quality compared to the CT128 and lower radiation dose parameters.