RPS 610 - Ultrasound, interventions and new techniques

Purpose:

To prospectively evaluate the accuracy of ultrasound in characterising superficial soft tissue tumours.

Methods and materials:

830 superficial soft tissue tumours were prospectively evaluated with ultrasound by 5 experienced musculoskeletal radiologists. The radiologist at the time of
examination provided 1-3 specific differential diagnoses and the perceived level of
confidence with regard to each diagnosis. The clinical diagnosis was recorded. Ultrasound and clinical diagnoses were compared with the histological diagnosis to determine the accuracy. Tumour malignancy was determined by histology or clinical follow-up.

Results:

234 (28.2%) of 830 tumours had a subsequent histological correlation. Compared with histology, the accuracy of clinical and ultrasound examination for determining the specific tumour type was 32.9% and 82.1%, respectively, considering all differential diagnoses provided. Radiologists were “fully confident” about the ultrasound diagnoses in 136 (58.1%) of 234 superficial soft tissue tumours and, in this setting, the diagnostic accuracy of ultrasound was 95.6%. When the radiologist was “not fully confident”, accuracy was 45.9% for the first
ultrasound differential diagnosis and 63.2% for all differential diagnoses. Sensitivity, specificity, positive predictive value, and negative predictive value of ultrasound for identifying malignant soft tissue tumours was 91.7%, 94.1%, 45.8%, and 99.5%, respectively.

Conclusion:

Based on the ultrasound appearances alone, the radiologist can be ‘fully
confident’ with providing a specific diagnosis in over half of the cases and, in this setting, diagnostic accuracy is very high. Ultrasound is also highly accurate at discriminating benign from malignant superficial soft tissue tumours.

Limitations:

Only one-quarter of tumours examined had a final histological diagnosis as it is common for soft tissue tumours with a clear diagnosis to forgo excision.

Moreover, a referral bias may have existed with more clinically atypical tumours referred for an ultrasound examination.

Ethics committee approval

This study was approved by the institutional review board.

Funding:

No funding was received for this work.

Purpose:

To evaluate callus formation and the role of Doppler in diaphyseal fractures of long bones treated by internal fixation.

Methods and materials:

100 patients with a diaphyseal fracture of long bones treated with internal fixation underwent ultrasonography of the fractured site at 6 weeks, 12 weeks, 18 weeks, and 24 weeks. The presence of callus and its echogenicity were evaluated. Doppler was applied to evaluate the vascularity within callus and spectral trace for the resistance index. Radiographs were obtained in AP and lateral views.

Results:

Out of the 100 patients evaluated, 87% progressed to union and 13% progressed to non-union of the fracture.

At 6 weeks, hypoechoic callus was seen in 83 patients progressing to union and 9 patients progressing to non-union. Callus formation on ultrasound at 6 weeks yielded a sensitivity and specificity of 95.4% and 69.2%, respectively. Callus on x-ray at 6 weeks yielded a sensitivity and specificity of 80.6% and 92.3%, respectively.

At 12 weeks, 100% of fractures demonstrated a hypoechoic callus with the presence of vascularity on the application of Doppler in 82% of uniting fractures and 84% of non-uniting fractures. The resistance index ranged from 0.56-0.89 in uniting fractures and 0.73-1.57 in non-uniting fractures, with cut-off below <0.88 yielding a sensitivity of 98% and specificity of 90%for uniting fractures.

At 18 weeks, 85% of patients progressing to union had a hyperechoic callus and 100% had a hyperechoic callus at 24 weeks.

Conclusion:

Ultrasound proved to be more sensitive for detecting the presence of early callus than radiographs. Colour Doppler and spectral trace add additional functional data on bone callus and neovascularisation with low resistive index in callus of uniting fractures.

Limitations:

Orthopaedic implants can limit the evaluation.

Ethics committee approval

Ethics committee approval obtained.

Funding:

No funding was received for this work.

Purpose:

To determine if dual-energy computerised tomography (DECT) was able to detect intra-articular monosodium urate (MSU) deposits, identified with ultrasonography (US), in patients with gout.

Methods and materials:

Knees of patients with a diagnosis of gout via US and DECT scans were prospectively assigned to DC+ or DC- groups depending on the presence or absence of the US double-contour sign (DC).

Standardised regions of interest were drawn in the patellofemoral joint space, the menisci, and the femorotibial cartilage. 5 DECT parameters were obtained: CT numbers in Hounsfield Unit (HU) at 80 and 140 kV, effective atomic number (Z_eff), electron density (ρ_e), and the dual-energy index (DEI). Zones were compared between the two groups using linear mixed models.

In a preliminary study, we used a phantom constituted of 3 rods of MSU (0, 200, and 600mg/ml) which were scanned to determine the in vitro DECT parameters of different concentrations of MSU.

Results:

115 patients were included. The mean gout duration was 9.0±9.8 years, mean serum urate level was 7.3±2.3 mg/dL, and mean DECT volume of urate deposition was 1.2cm³±3.8. 225 knees were analysed. 36 knees were assigned to the DC+ group.

No significant differences were found between DC+ and DC- knees for Zeff, ρe, and DEI in menisci (p=0.94, 0.72, and 0.97, respectively), femorotibial cartilage (p=0.94, 0.89, and 0.97, respectively), or patellofemoral joint space (p= 0.48, 0.89, and 0.54, respectively).

Phantoms exhibited increasing values in ρ_e (p=0.03) with growing MSU concentrations.

Conclusion:

This study shows that, in vivo, DECT is not able to identify intra-articular MSU deposition in patients with gout, although it has the ability to detect in vitro growing concentrations of MSU.

Limitations:

n/a

Ethics committee approval

n/a

Funding:

No funding was received for this work.

Purpose:

To analyse changes in the apparent diffusion coefficient in patients with specific low back pain following CT-guided interventional therapy.

Methods and materials:

From 11/2017-2/2018, 14 MRI examinations in 7 patients suffering from low back pain were compared before and after CT-guided periradicular infiltration therapy in respect to the ADC value of the affected and treated nerve root. Two radiologists independently measured the ADC value of the affected nerve twice and the mean value was calculated. Before and, in average, 11 days after CT-guided treatment where a glucocorticoid, a local anaesthetic, and a contrast agent were injected close to the affected nerve root, the same nerve root was measured. The affected nerve root was compared by the same procedure to a non-affected nerve root. We asked the patients before each intervention to point out their actual pain on an analogue pain score ranging from 0-10. We calculated the correlation between the change in ADC value and the development of the pain score as a one-sided Pearson correlation.

Results:

There is a strong negative correlation of -0.698 (p=0.017) between the change of ADC value and the improvement of the pain score under therapy. For the reference nerve, no significant change of ADC over time was shown.

Conclusion:

Effective periradicular CT-guided infiltration leads to a significant ADC increase of the affected nerve.

Limitations:

The small number of patients.

Ethics committee approval

The presented study was approved by the local ethic committee.

Funding:

No funding was received for this work.

Purpose:

To present our experience in the treatment of chondroblastoma by radiofrequency thermal ablation.

Methods and materials:

In the last 15 years, we treated 9 patients (8 males) with chondroblastoma using RTA under CT-guidance. Tumours were located in the humeral head (3), the femoral head (2), and the distal femoral epiphysis (4). Age ranged from 11-20 years (median: 15 years). Tumour size ranged from 12-34 mm (median: 22 mm).

According to tumour size and location, the electrode’s active tip ranged from 1-3 cm. Dry ablation or perfused monopolar electrodes were used to treat smaller (6) and larger (3) lesions, respectively. Cementation was added in 3 cases.

Imaging follow-up was performed by MRI (7), CT (1), and radiography (9). Follow-up ranged from 6 months to 15 years.

Results:

Total pain control was achieved in all cases. A follow-up MRI demonstrated resolution of oedema, as well as a necrotic area extending beyond the outer edge of the lesion. Radiography showed stability of the lesions, with increased sclerosis and no cortex collapse.

In one case, a 4 cm shortening of the humerus was observed at the end of skeletal development (7 years after treatment). In another case, early hip osteoarthritis was developed (15 years after treatment).

Conclusion:

Successful treatment of chondroblastoma can be achieved by RTA. MRI hallmarks associated with clinical success were resolution of bone marrow oedema and an area of necrosis extending beyond the tumour edge. Radiography remains a useful exam to demonstrate cortex integrity.

Limitations:

A retrospective review of the cases, although data and images were acquired prospectively, according to hospital clinical protocols.

Ethics committee approval

This work was approved by the local ethics committee (0847-N-19).

Funding:

No funding was received for this work.

Purpose:

To investigate the effect of circular and elliptical polarisation of the radiofrequency (RF) pulse on metal-related artefacts in total hip arthroplasty implants during a metal artefact reduction sequence MRI at 3T.

Methods and materials:

A cobalt-chromium total hip arthroplasty system with a polyethylene liner immersed in a standard ASTM gel phantom underwent an MRI with high-bandwidth turbo spin-echo (HBW-TSE), slice encoding for metal artefact correction (SEMAC), and compressed sensing (CS) SEMAC in axial, coronal, and sagittal planes using proton density weighting. Each scan was acquired twice with circular (CP) and elliptical (EP) RF polarisation, while keeping other sequence parameters identical. After anonymisation/randomisation, artefacts were volumetrically quantified for CP and EP images using manual segmentation. Additionally, observers compared the two modes for overall image quality through a side-by-side display of each image pair and selection of the preferred polarisation mode.

Results:

On quantitative analysis, artefact degraded regions were significantly smaller on EP images compared to the CP images of the same location/pulse sequence (paired t-test: p<0.02 for all pulse sequences). The overall artefact volume (including the implant itself) calculated using axial HBW-TSE images was 19% lower for EP (510 cm³) compared to CP (608 cm³). Readers chose the image quality of EP in 56% (95% CI: 51%-61%) and CP in 7% (95% CI: 4%-9%) of the cases with significantly superior image quality of EP (signed test: p<0.001 for all sequences).

Conclusion:

3T MRI with elliptical RF pulse polarisation results in stronger metal artefact reduction and overall superior image quality than circular polarisation. Switching to elliptical polarisation for 3T imaging of metal-containing body parts may eventually hold promise for in vivo clinical imaging.

Limitations:

The in-vitro nature of the study.

Ethics committee approval

n/a

Funding:

RSNA fellow research grant.

Purpose:

To quantitatively assess the image quality of reduced-dose CBCT images, reconstructed with different levels of adaptive image noise optimiser (AINO).

Methods and materials:

A fresh frozen cadaver lower leg was scanned on a Planmed verity cone-beam CT-scanner using ultra-low-dose parameters of 0.4 mm resolution, 300 projections, 15 ms pulse length, and a sharp reconstruction kernel. The kV was varied between 96–80 and mA was reduced from 6.3 to 4, 2, and 1 mA. Acquisitions were reconstructed without AINO and with AINO (levels light/medium/strong), which resulted in a total of 80 reconstructions. CT-numbers, standard deviations as a noise estimate, and contrast-to-noise-ratios (CNR) were quantitatively assessed in regions-of-interest placed in the bone and soft tissue. Quantitative results of standard protocol images using 96kV and 6.3mA, without AINO, served as a reference.

Results:

CTDI_vol reduced 92%, from 2.74 mGy in 96kV/6.3mA acquisitions to 0.21 mGy in 80kV/1mA acquisitions. Standard deviations and CNR decreased while CT-numbers remained constant in reduced-dose results. AINO reduced standard deviations of noise, and increased CNR, while CT numbers remained constant. Increasing levels of AINO results in higher CNR (p<0.001). Based on the quantitative analysis on CNR, AINO potentially enables a radiation dose reduction of 15-85%, depending on the level of AINO, kV, and mA. Photon-starvation artefacts appear at low kV and mA.

Conclusion:

Based on the quantitative analysis on CNR, AINO potentially enables a radiation dose reduction of 15-85%, depending on the level of AINO, kV, and mA. However, AINO is incapable of eliminating photon-starvation artefacts and images appear smoother due to noise reduction.

Limitations:

The sample size and quantitative assessment of image quality only.

Ethics committee approval

n/a

Funding:

No funding was received for this work.