3D cone-beam CT of the ankle using a novel twin robotic X-ray system: Assessment of image quality and radiation dose

A systematic review comparing the effective radiation dose of musculoskeletal cone beam computed tomography to other diagnostic imaging modalities

PURPOSE

Cone-Beam CT (CBCT) is well established in orofacial diagnostic imaging and is currently expanding into musculoskeletal applications. This systematic review sought to update the knowledge base on radiation dose comparisons between imaging modalities in MSK imaging and consider how research studies have reported dose measures.

METHODS

This review utilised a database search and an online literature tool. Studies with potential relevance were screened then before full text review, each performed by two independent reviewers, with a third independent reviewer available for conflicts. Data was extracted using a bespoke tool created within the literature tool.

RESULTS

21 studies were included in the review which compared CBCT with MSCT (13), conventional radiography (1), or both (7). 19 studies concluded that CBCT provided a reduced radiation dose when compared with MSCT: the factor of reduction ranging from 1.71 to 50 with an average of 12. Studies comparing CBCT to DR found DR to have an average dose reduction of 4.55.

CONCLUSIONS

The claims that CBCT produces a lower radiation dose than MSCT is borne out with most studies confirming doses less than half that of MSCT. Fewer studies include DR as a comparator but confirm that CBCT results in a higher effective dose on average, with scope for CBCT to provide an equivalent radiation dose. This review highlighted a need for consistency in methodology when conducting studies which compare radiation dose across different technologies. Potential solutions lie outside the scope of this review, likely requiring multi-discipline approach to ensure a cohesive outcome.

Generating patient-matched 3D-printed pedicle screw and laminectomy drill guides from Cone Beam CT images: Studies in ovine and porcine cadavers

Background

The emergence of robotic Cone Beam Computed Tomography (CBCT) imaging systems in trauma departments has enabled 3D anatomical assessment of musculoskeletal injuries, supplementing conventional 2D fluoroscopic imaging for examination, diagnosis, and treatment planning. To date, the primary focus has been on trauma sites in the extremities.

Purpose

To determine if CBCT images can be used during the treatment planning process in spinal instrumentation and laminectomy procedures, allowing accurate 3D‐printed pedicle screw and laminectomy drill guides to be generated for the cervical and thoracic spine.

Methods

The accuracy of drill guides generated from CBCT images was assessed using animal cadavers (ovine and porcine). Preoperative scans were acquired using a robotic CBCT C‐arm system, the Siemens ARTIS pheno (Siemens Healthcare, GmbH, Germany). The CBCT images were imported into 3D‐Slicer version 4.10.2 (www.slicer.org) where vertebral models and specific guides were developed and subsequently 3D‐printed. In the ovine cadaver, 11 pedicle screw guides from the T1–T5 and T7–T12 vertebra and six laminectomy guides from the C2–C7 vertebra were planned and printed. In the porcine cadaver, nine pedicle screw guides from the C3–T4 vertebra were planned and printed. For the pedicle screw guides, accuracy was assessed by three observers according to pedicle breach via the Gertzbein–Robbins grading system as well as measured mean axial and sagittal screw error via postoperative CBCT and CT scans. For the laminectomies, the guides were designed to leave 1 mm of lamina. The average thickness of the lamina at the mid‐point was used to assess the accuracy of the guides, measured via postoperative CBCT and CT scans from three observers. For all measurements, the intraclass correlation coefficient (ICC) was calculated to determine observer reliability.

Results

Compared with the planned screw angles for both the ovine and porcine procedures (n = 32), the mean axial and sagittal screw error measured on the postoperative CBCT scans from three observers were 3.9 ± 1.9° and 1.8 ± 0.8°, respectively. The ICC among the observes was 0.855 and 0.849 for the axial and sagittal measurements, respectively, indicating good reliability. In the ovine cadaver, directly comparing the measured axial and sagittal screw angle of the visible screws (n = 14) in the postoperative CBCT and conventional CT scans from three observers revealed an average difference 1.9 ± 1.0° in axial angle and 1.8 ± 1.0° in the sagittal angle. The average thickness of the lamina at the middle of each vertebra, as measured on‐screen in the postoperative CBCT scans by three observes was 1.6 ± 0.2 mm. The ICC among observers was 0.693, indicating moderate reliability. No lamina breaches were observed in the postoperative images.

Conclusion

Here, CBCT images have been used to generate accurate 3D‐printed pedicle screw and laminectomy drill guides for use in the cervical and thoracic spine. The results demonstrate sufficient precision compared with those previously reported, generated from standard preoperative CT and MRI scans, potentially expanding the treatment planning capabilities of robotic CBCT imaging systems in trauma departments and operating rooms.

Evaluation of Ultra-High-Resolution Cone-Beam CT Prototype of Twin Robotic Radiography System for Cadaveric Wrist Imaging

RATIONALE AND OBJECTIVES

Cone-beam CT (CBCT) applications possess potential for dose reduction in musculoskeletal imaging. This study evaluates the ultra-high-resolution CBCT prototype of a twin robotic X-ray system in wrist examinations compared to high-resolution multidetector CT (MDCT).

MATERIALS AND METHODS

Sixteen wrists of body donors were examined with the CBCT scan mode and a 384 slice MDCT system. Radiation-equivalent low-dose (CTDI_vol(16cm)  = 3.3 mGy) and full-dose protocols (CTDI_vol(16cm)  = 13.8 mGy) were used for both systems. Two observers assessed image quality on a seven-point Likert scale. In addition, software-assisted quantification of signal intensity fractions in cancellous bone was performed. Fewer pixels with intermediate signal intensity were considered to indicate superior depiction of bone microarchitecture.

RESULTS

Subjective image quality in CBCT was superior to dose equivalent MDCT with p ≤ 0.03 for full-dose and p < 0.001 for low-dose scans, respectively. Median Likert values were 7/7 (reader 1 / reader 2) in full-dose CBCT, 6/6 in full-dose MDCT, 5/6 in low-dose CBCT and 3/3 in low-dose MDCT. Intraclass correlation coefficient was 0.936 (95% confidence interval, 0.897-0.961; p < 0.001), indicating excellent reliability. Objective analysis displayed smaller fractions of "indecisive" pixels with intermediate signal intensity for full-dose CBCT (0.57 [interquartile range 0.13]) compared to full-dose MDCT (0.68 [0.21]), low-dose CBCT (0.72 [0.19]), and low-dose MDCT (0.80 [0.15]) studies. No significant difference was observed between low-dose CBCT and full-dose MDCT.

CONCLUSION

The new CBCT prototype provides superior image quality for trabecula and bone marrow in cadaveric wrist studies and enables dose reduction up to 75% compared to high-resolution MDCT.

Twin robotic x-ray system in small bone and joint trauma: impact of cone-beam computed tomography on treatment decisions

Objectives

Trauma evaluation of extremities can be challenging in conventional radiography. A multi-use x-ray system with cone-beam CT (CBCT) option facilitates ancillary 3-D imaging without repositioning. We assessed the clinical value of CBCT scans by analyzing the influence of additional findings on therapy.

Methods

Ninety-two patients underwent radiography and subsequent CBCT imaging with the twin robotic scanner (76 wrist/hand/finger and 16 ankle/foot/toe trauma scans). Reports by on-call radiologists before and after CBCT were compared regarding fracture detection, joint affliction, comminuted injuries, and diagnostic confidence. An orthopedic surgeon recommended therapy based on reported findings. Surgical reports (N = 52) and clinical follow-up (N = 85) were used as reference standard.

Results

CBCT detected more fractures (83/64 of 85), joint involvements (69/53 of 71), and multi-fragment situations (68/50 of 70) than radiography (all p < 0.001). Six fractures suspected in radiographs were ruled out by CBCT. Treatment changes based on additional information from CBCT were recommended in 29 patients (31.5%). While agreement between advised therapy before CBCT and actual treatment was moderate (κ = 0.41 [95% confidence interval 0.35–0.47]; p < 0.001), agreement after CBCT was almost perfect (κ = 0.88 [0.83–0.93]; p < 0.001). Diagnostic confidence increased considerably for CBCT studies (p < 0.001). Median effective dose for CBCT was 4.3 μSv [3.3–5.3 μSv] compared to 0.2 μSv [0.1–0.2 μSv] for radiography.

Conclusions

CBCT provides advantages for the evaluation of acute small bone and joint trauma by detecting and excluding extremity fractures and fracture-related findings more reliably than radiographs. Additional findings induced therapy change in one third of patients, suggesting substantial clinical impact.

Key Points

• With cone-beam CT, extremity fractures and fracture-related findings can be detected and ruled out more reliably than with conventional radiography.

• Additional diagnostic information provided by cone-beam CT scans has substantial impact on therapy in small bone and joint trauma.

• For distal extremity injury assessment, one-stop-shop imaging without repositioning is feasible with the twin robotic x-ray system.

Comparison of 3D X-ray tomography with computed tomography in patients with distal extremity fractures

OBJECTIVE

To compare fracture detection, image quality, and radiation dose in patients with distal extremity fractures using 3D tomography and computed tomography (CT).

MATERIALS AND METHODS

IRB approval was obtained including informed consent for this prospective study from June to December 2016. Patients diagnosed with an acute fracture at CT were consecutively scanned on the same day using 3D tomography. Anatomical location (effected bone and location within the bone) and morphological characteristics of fractures (avulsion, articular involvement, mono- vs. multifragmented, displacement), visibility of bone/soft tissue structures, and image quality were assessed independently by two blinded readers on a 5-point Likert scale. Dose-length-product (DLP; mGy*cm) was compared between both modalities. Descriptive statistics, Wilcoxon signed rank test (P < 0.05), Student's t test (P < 0.05), and Cohen's kappa (κ) for interreader reliability were calculated.

RESULTS

In 46 patients (28 males; 18 females; mean age, 53 ± 20 years) with 28 hand/wrist and 18 foot/ankle examinations, 86 out of 92 fractures were diagnosed with 3D tomography compared with CT. No false-positive finding occurred at 3D tomography. The six missed fractures on 3D tomography were five avulsion fractures of the carpals/metacarpals or tarsals/metatarsals, respectively, and one nondisplaced fracture of the capitate. Interreader agreement of anatomical location and morphological characteristics was substantial to almost perfect for upper (κ = 0.80-0.96) and lower (κ = 0.70-0.97) extremity fractures. Visibility of bone and soft tissue structures and image quality were slightly inferior using 3D tomography compared with CT (upper extremity P < 0.001-0.038 and lower extremity P < 0.001-0.035). DLP of a comparable scan coverage was significantly lower for 3D tomography (P < 0.001) for both upper (3D mean, 19.4 ± 5.9 mGy*cm; estimated CT mean, 336.5 ± 52.2 mGy*cm) and lower extremities (3D mean, 24.1 ± 11.1 mGy*cm; estimated CT mean, 182.9 ± 6.5 mGy*cm). Even the highest DLP with 3D tomography was < 30% of the mean estimated CT dose of a comparable area of coverage.

CONCLUSION

Fracture assessment of peripheral extremities is reliable utilizing a low-dose 3D tomography X-ray system, with slightly reduced image quality.

In vivo 3D tomography of the lumbar spine using a twin robotic X-ray system: quantitative and qualitative evaluation of the lumbar neural foramina in supine and upright position

OBJECTIVES

Supine lumbar spine examinations underestimate body weight effects on neuroforaminal size. Therefore, our purpose was to evaluate size changes of the lumbar neuroforamina using supine and upright 3D tomography and to initially assess image quality compared with computed tomography (CT).

METHODS

The lumbar spines were prospectively scanned in 48 patients in upright (3D tomographic twin robotic X-ray) and supine (30 with 3D tomography, 18 with CT) position. Cross-sectional area (CSA), cranio-caudal (CC), and ventro-dorsal (VD) diameters of foramina were measured by two readers and additionally graded in relation to the intervertebral disc height. Visibility of bone/soft tissue structures and image quality were assessed independently on a 5-point Likert scale for the 18 patients scanned with both modalities. Descriptive statistics, Wilcoxon's signed-rank test (p < 0.05), and interreader reliability were calculated.

RESULTS

Neuroforaminal size significantly decreased at all levels for both readers from the supine (normal intervertebral disc height; CSA 1.25 ± 0.32 cm²; CC 1.84 ± 0.24 cm²; VD 0.88 ± 0.16 cm²) to upright position (CSA 1.12 ± 0.34 cm²; CC 1.78 ± 0.24 cm²; VD 0.83 ± 0.16 cm²; each p < 0.001). Decrease in intervertebral disc height correlated with decrease in foraminal size (supine: CSA 0.88 ± 0.34 cm²; CC 1.39 ± 0.33 cm²; VD 0.87 ± 0.26 cm²; upright: CSA 0.83 ± 0.37 cm², p = 0.010; CC 1.32 ± 0.33 cm², p = 0.015; VD 0.80 ± 0.21 cm², p = 0.021). Interreader reliability for area was fair to excellent (0.51-0.89) with a wide range for cranio-caudal (0.32-0.74) and ventro-dorsal (0.03-0.70) distances. Image quality was superior for CT compared with that for 3D tomography (p < 0.001; κ, CT = 0.66-0.92/3D tomography = 0.51-1.00).

CONCLUSIONS

The size of the lumbar foramina is smaller in the upright weight-bearing position compared with that in the supine position. Image quality, especially nerve root delineation, is inferior using 3D tomography compared to CT.

KEY POINTS

• Weight-bearing examination demonstrates a decrease of the neuroforaminal size. • Patients with higher decrease in intervertebral disc showed a narrower foraminal size. • Image quality is superior with CT compared to 3D tomographic twin robotic X-ray at the lumbar spine.

3D cone-beam CT with a twin robotic x-ray system in elbow imaging: comparison of image quality to high-resolution multidetector CT

Background

Elbow imaging is challenging with conventional multidetector computed tomography (MDCT), while cone-beam CT (CBCT) provides superior options. We compared intra-individually CBCT versus MDCT image quality in cadaveric elbows.

Methods

A twin robotic x-ray system with new CBCT mode and a high-resolution clinical MDCT were compared in 16 cadaveric elbows. Both systems were operated with a dedicated low-dose (LD) protocol (equivalent volume CT dose index [CTDI_{vol(16 cm)}] = 3.3 mGy) and a regular clinical scan dose (RD) protocol (CTDI_{vol(16 cm)} = 13.8 mGy). Image quality was evaluated by two radiologists (R1 and R2) on a seven-point Likert scale, and estimation of signal intensity in cancellous bone was conducted. Wilcoxon signed-rank tests and intraclass correlation coefficient (ICC) statistics were used.

Results

The CBCT prototype provided superior subjective image quality compared to MDCT scans (for RD, p ≤ 0.004; for LD, p ≤ 0.001). Image quality was rated very good or excellent in 100% of the cases by both readers for RD CBCT, 100% (R1) and 93.8% (R2) for LD CBCT, 62.6% and 43.8% for RD MDCT, and 0.0% and 0.0% for LD MDCT. Single-measure ICC was 0.95 (95% confidence interval 0.91–0.97; p < 0.001). Software-based assessment supported subjective findings with less “undecided” pixels in CBCT than dose-equivalent MDCT (p < 0.001). No significant difference was found between LD CBCT and RD MDCT.

Conclusions

In cadaveric elbow studies, the tested cone-beam CT prototype delivered superior image quality compared to high-end multidetector CT and showed a potential for considerable dose reduction.

Validation of radiological reduction criteria with intraoperative cone beam CT in unstable syndesmotic injuries

Purpose

Acute unstable syndesmotic lesions are regularly treated with closed or open reduction and fixation with either a positioning screw or tight rope. Conventional fluoroscopy is limited to identify a malreduction of the ankle mortise. The aim of the study was to validate the reduction criteria of intraoperative cone beam CT in unstable syndesmotic injuries by analyzing the clinical outcome.

Methods

Acute unstable syndesmotic injuries were treated with a positioning screw fixation, and the reduction in the ankle mortise was evaluated with intraoperative cone beam CT. The patients were grouped postoperatively according to the radiological reduction criteria in the intraoperative 3D images. The reduction criteria were unknown to the surgeons. Malreduction was assumed if one or more reduction criteria were not fulfilled.

Results

Seventy-three of the 127 patients could be included in the study (follow-up rate 57.5%). For 41 patients (56.2%), a radiological optimal reduction was achieved (Group 1), and in 32 patients (43.8%) a radiological adverse reduction was found (Group 2). Group 1 scored significantly higher in the Olerud/Molander score (92.44 ± 10.73 vs. 65.47 ± 28.77) (p = 0.003), revealed a significantly higher range of motion (ROM) (53.44 vs. 24.17°) (p = 0.001) and a significantly reduced Kellgren/Lawrence osteoarthritis score (1.24 vs. 1.79) (p = 0.029). The linear regression analysis revealed a correlation for the two groups with the values scored in the Olerud/Molander score (p < 0.01).

Conclusion

The reduction criteria in intraoperative cone beam CT applied to unstable syndesmotic injuries could be validated. Patients with an anatomic reduced acute unstable syndesmotic injury according to the criteria have a significantly better clinical outcome.