Novel developments in non-invasive imaging of peripheral arterial disease with CT: experience with state-of-the-art, ultra-high-resolution CT and subtraction imaging

Infrapopliteal Segments on Lower Extremity CTA: Prospective Intraindividual Comparison of Energy-Integrating Detector CT and Photon-Counting Detector CT

BACKGROUND. The higher spatial resolution and image contrast for iodine-containing tissues of photon-counting detector (PCD) CT may address challenges in evaluating small calcified vessels when performing lower extremity CTA by energy-integrating detector (EID) CTA. OBJECTIVE. The purpose of the study was to compare the evaluation of infrapopliteal vasculature between lower extremity CTA performed using EID CT and PCD CT. METHODS. This prospective study included 32 patients (mean age, 69.7 ± 11.3 [SD] years; 27 men, five women) who underwent clinically indicated lower extremity EID CTA between April 2021 and March 2022; participants underwent investigational lower extremity PCD CTA later the same day as EID CTA using a reduced IV contrast media dose. Two radiologists independently reviewed examinations in two sessions, each containing a random combination of EID CTA and PCD CTA examinations; the readers assessed the number of visualized fibular perforators, characteristics of stenoses at 11 infrapopliteal segmental levels, and subjective arterial sharpness. RESULTS. Mean IV contrast media dose was 60.0 ± 11.0 (SD) mL for PCD CTA versus 139.6 ± 11.8 mL for EID CTA (p < .001). The number of identified fibular perforators per lower extremity was significantly higher for PCD CTA than for EID CTA for reader 1 (R1) (mean ± SD, 6.4 ± 3.2 vs 4.2 ± 2.4; p < .001) and reader 2 (R2) (8.8 ± 3.4 vs 7.6 ± 3.3; p = .04). Reader confidence for assessing stenosis was significantly higher for PCD CTA than for EID CTA for R1 (mean ± SD, 82.3 ± 20.3 vs 78.0 ± 20.2; p < .001) but not R2 (89.8 ± 16.7 vs 90.6 ± 7.1; p = .24). The number of segments per lower extremity with total occlusion was significantly lower for PCD CTA than for EID CTA for R2 (mean ± SD, 0.5 ± 1.3 vs 0.9 ± 1.7; p = .04) but not R1 (0.6 ± 1.3 vs 1.0 ± 1.5; p = .07). The number of segments per lower extremity with clinically significant nonocclusive stenosis was significantly higher for PCD CTA than for EID CTA for R1 (mean ± SD, 2.2 ± 2.2 vs 1.6 ± 1.7; p = .01) but not R2 (1.1 ± 2.0 vs 1.1 ± 1.4; p = .89). Arterial sharpness was significantly greater for PCD CTA than for EID CTA for R1 (mean ± SD, 3.2 ± 0.5 vs 1.8 ± 0.5; p < .001) and R2 (3.2 ± 0.4 vs 1.7 ± 0.8; p < .001). CONCLUSION. PCD CTA yielded multiple advantages relative to EID CTA for visualizing small infrapopliteal vessels and characterizing associated plaque. CLINICAL IMPACT. The use of PCD CTA may improve vascular evaluation in patients with peripheral arterial disease.

First experience of evaluation of the impact of high-matrix size reconstruction in image quality in arterial CT runoff studies of the lower extremities

OBJECTIVES

To determine whether image reconstruction with a higher matrix size improves image quality for lower extremity CTA studies.

METHODS

Raw data from 50 consecutive lower extremity CTA studies acquired on two MDCT scanners (SOMATOM Flash, Force) in patients evaluated for peripheral arterial disease (PAD) were retrospectively collected and reconstructed with standard (512 × 512) and higher resolution (768 × 768, 1024 × 1024) matrix sizes. Five blinded readers reviewed representative transverse images in randomized order (150 total). Readers graded image quality (0 (worst)-100 (best)) for vascular wall definition, image noise, and confidence in stenosis grading. Ten patients' stenosis scores on CTA images were compared to invasive angiography. Scores were compared using mixed effects linear regression.

RESULTS

Reconstructions with 1024 × 1024 matrix were ranked significantly better for wall definition (mean score 72, 95% CI = 61-84), noise (74, CI = 59-88), and confidence (70, CI = 59-80) compared to 512 × 512 (wall = 65, CI = 53 × 77; noise = 67, CI = 52 × 81; confidence = 62, CI = 52 × 73; p = 0.003, p = 0.01, and p = 0.004, respectively). Compared to 512 × 512, the 768 × 768 and 1024 × 1024 matrix improved image quality in the tibial arteries (wall = 51 vs 57 and 59, p < 0.05; noise = 65 vs 69 and 68, p = 0.06; confidence = 48 vs 57 and 55, p < 0.05) to a greater degree than the femoral-popliteal arteries (wall = 78 vs 78 and 85; noise = 81 vs 81 and 84; confidence = 76 vs 77 and 81, all p > 0.05), though for the 10 patients with angiography accuracy of stenosis grading was not significantly different. Inter-reader agreement was moderate (rho = 0.5).

CONCLUSION

Higher matrix reconstructions of 768 × 768 and 1024 × 1024 improved image quality and may enable more confident assessment of PAD.

CLINICAL RELEVANCE STATEMENT

Higher matrix reconstructions of the vessels in the lower extremities can improve perceived image quality and reader confidence in making diagnostic decisions based on CTA imaging.

KEY POINTS

• Higher than standard matrix sizes improve perceived image quality of the arteries in the lower extremities. • Image noise is not perceived as increased even at a matrix size of 1024 × 1024 pixels. • Gains from higher matrix reconstructions are higher in smaller, more distal tibial and peroneal vessels than in femoropopliteal vessels.

Combined evaluation of blood flow and tissue perfusion in diabetic feet by intra-arterial dynamic 4DCT imaging

Critical limb ischemia is associated with high mortality and major amputations. Intra-arterial digital subtraction angiography (IADSA) has been the reference standard but has some shortcomings including the two-dimensional projection and the lack of tissue perfusion information. The aim of this exploratory study is to examine four-dimensional computed tomography (4DCT) angiography and perfusion imaging using low-volume intra-arterial contrast injections for an improved anatomic and hemodynamic assessment in patients with foot ulcers. Three patients underwent a low-volume (2 mL) intra-arterial contrast-enhanced 4DCT examination combined with a diagnostic IADSA. An automated assessment of blood flow and tissue perfusion from the 4DCT data was performed. Vascular structures and corresponding blood flows were successfully assessed and correlated well with the IADSA results. Perfusion values of the affected tissue were significantly higher compared to the unaffected tissue. The proposed 4DCT protocol combined with the minimal usage of contrast agent (2 mL) provides superior images compared to IADSA as three phases (arterial, perfusion, and venous) are captured. The obtained parameters could allow for an improved diagnosis of critical limb ischemia as both the proximal vasculature and the extent of the perfusion deficit in the microvasculature can be assessed.Relevance statementIntra-arterial 4DCT allows for assessing three phases (arterial, perfusion and venous) using minimal contrast (2 mL). This method could lead to an improved diagnosis of critical limb ischemia as both proximal vasculature and the extent of the perfusion deficit are assessed.Trial registrationISRCTN, ISRCTN95737449. Registered 14 March 2023-retrospectively registered, https://www.isrctn.com/ISRCTN95737449 Key points• Three phases (arterial, perfusion, and venous) are obtained from 2 mL intra-arterial 4DCT.• The obtained hemodynamic parameters correlated well with the IADSA findings.• 4DCT surpassed IADSA in terms of assessment of venous blood flow and inflammatory hyperperfusion.• The assessment of tissue perfusion could lead to optimizing the revascularization strategy.

Association between psoriasis and peripheral artery occlusive disease: a population-based retrospective cohort study

Introduction

Psoriasis (PSO) is a chronic skin condition that affects a variety of disorders, especially the cardiovascular system. This study investigated the association between PSO and peripheral arterial disease (PAOD).

Methods

A retrospective cohort study design was carried out between 2000 and 2018. The exposure subject was a newly diagnosed PSO. The diagnosis of PSO was never elaborated as a comparison subject. Balanced heterogeneity of the two groups was used by propensity score matching. The cumulative incidence of PAOD between the two groups was performed using Kaplan-Meier analysis. The Cox proportional hazard model was used to measure the risk of PAOD risk hazard ratio.

Results

After matching the 1: 1 propensity score, 15,696 subjects with PSO and the same number of subjects without the diagnosis of PSO were recruited. The PSO subject had a higher risk of PAOD than the non-PSO subject (adjusted HR = 1.25; 95% CI = 1.03-1.50). In the 40-64-year-old subgroup, the subject of PSO exhibited an increased risk of PAOD than the subject without PSO.

Conclusion

Psoriasis is associated with an increased risk of peripheral arterial disease and curative care is necessary to reduce the risk of PAOD..

Dual-Source Photon-Counting Computed Tomography-Part III: Clinical Overview of Vascular Applications beyond Cardiac and Neuro Imaging

Photon-counting computed tomography (PCCT) is an emerging technology that is expected to radically change clinical CT imaging. PCCT offers several advantages over conventional CT, which can be combined to improve and expand the diagnostic possibilities of CT angiography. After a brief description of the PCCT technology and its main advantages we will discuss the new opportunities brought about by PCCT in the field of vascular imaging, while addressing promising future clinical scenarios.

Risk of Peripheral Arterial Occlusive Disease with Periodontitis and Dental Scaling: A Nationwide Population-Based Cohort Study

Periodontitis (PD) is a common oral disease associated with various other diseases, particularly those affecting the cardiovascular system. This study explored whether peripheral artery occlusive disease (PAOD) is associated with PD and dental scaling. This study was a retrospective cohort study design from 2000 to 2018. The study population was newly diagnosed with periodontitis. The comparison group was defined as never diagnosed with periodontitis. The outcome variable was defined with the diagnosis of peripheral arterial occlusive disease (PAOD). The propensity score matching was performed by age, sex, comorbidities, and dental scaling between the two groups. Kaplan-Meier analysis was used to calculate the cumulative incidence of PAOD among the two groups. To perform the independent risk of the PAOD group, the multivariate Cox proportional hazard model was used to estimate the hazard ratios. First, 792,681 patients with PD and 458,521 patients with no history of PD were selected from Taiwan's Longitudinal Health Insurance Database, which comprises the data of two million beneficiaries. After propensity score matching between the PD and non-PD groups for age, sex, comorbidities, and dental scaling, 357,106 patients in each group were analyzed for PAOD risk. The incidence density, relative risk, and cumulative incidence of PAOD were higher in the PD group than in the non-PD group. After adjusting for all variables, the risk of PAOD for the PD group was greater than for the non-PD group (adjusted hazard ratio = 1.03; 95% CI, 1.01-1.06). Undergoing at least one dental scaling procedure reduced the risk of PAOD. Age over 65 years was also a risk factor. In conclusion, patients with PD have an increased risk of PAOD. In addition, our results can lead to increased attention to oral hygiene, as dental scaling has a trend towards a lower risk of PAOD.

Influence of CT Image Matrix Size and Kernel Type on the Assessment of HRCT in Patients with SSC-ILD

Background: Interstitial lung disease (ILD) is a frequent complication of systemic sclerosis (SSc), and its early detection and treatment may prevent deterioration of lung function. Different vendors have recently made larger image matrices available as a post-processing option for computed tomography (CT), which could facilitate the diagnosis of SSc-ILD. Therefore, the objective of this study was to assess the effect of matrix size on lung image quality in patients with SSc by comparing a 1024-pixel matrix to a standard 512-pixel matrix and applying different reconstruction kernels. Methods: Lung scans of 50 patients (mean age 54 years, range 23−85 years) with SSc were reconstructed with these two different matrix sizes, after determining the most appropriate kernel in a first step. Four observers scored the images on a five-point Likert scale regarding image quality and detectability of clinically relevant findings. Results: Among the eight tested kernels, the Br59-kernel (sharp) reached the highest score (19.48 ± 3.99), although differences did not reach statistical significance. The 1024-pixel matrix scored higher than the 512-pixel matrix HRCT overall (p = 0.01) and in the subcategories sharpness (p < 0.01), depiction of bronchiole (p < 0.01) and overall image impression (p < 0.01), and lower for the detection of ground-glass opacities (GGO) (p = 0.04). No significant differences were found for detection of extent of reticulations/bronchiectasis/fibrosis (p = 0.50) and image noise (p = 0.09). Conclusions: Our results show that with the use of a sharp kernel, the 1024-pixel matrix HRCT, provides a slightly better subjective image quality in terms of assessing interstitial lung changes, whereby GGO are more visible on the 512-pixel matrix. However, it remains to be answered to what extent this is related to the improved representation of the smallest structures.

Performance of Ultra-High-Resolution Computed Tomography in Super High-Resolution Mode at the Routine Radiation Dose: Phantom Study

OBJECTIVE

Using a chest phantom, we compared the image quality of ultra-high-resolution computed tomography (U-HRCT) images acquired in super high-resolution (SHR) and normal resolution (NR) mode and at the routine radiation dose. The detector size was 0.25 and 0.5 mm, respectively.

METHODS

A chest phantom was scanned on a U-HRCT scanner. The scan parameters were tube voltage 120 kV and volume CT dose index 13.0 mGy, the routine radiation dose for conventional scans. The rotation time was 0.5 s/rot, the number of matrices was 512 in NR and 1024 in SHR mode. For physical evaluation, the modulation transfer function was measured on the spherical simulated nodule, and the noise power spectrum on the cylindrical water phantom. A CT value profile curve was created using an in-house simulated bronchial phantom. For visual evaluation, 3 radiologists and 3 radiology technologists evaluated overall image quality using a 4-grade scale (grade 1, poor; and grade 4, excellent).

RESULTS

The 10% of modulation transfer function was 13.5 lp/cm in NR and 14.9 lp/cm in SHR mode (P<0.01). ƒpeak was 5.6 lp/cm in NR and 8.8 lp/cm in SHR mode (P<0.01), and the peak of noise power spectrum shifted. On the profile curves, the CT value at the edge changed in NR but not in SHR mode. The overall image quality was grade 3.0 ± 0.7 in SHR and grade 2.0 ± 0.7 in NR mode (P<0.01).

CONCLUSIONS

The image quality of SHR mode with U-HRCT was superior to that of NR mode at the routine radiation dose.

Influence of monitor display resolution and displayed image size on the spatial resolution of ultra-high-resolution CT images: a phantom study

To determine the optimal display conditions for ultra-high-resolution computed tomography (UHRCT) images in clinical practice, this study investigated the effects of liquid-crystal display (LCD) resolution and displayed image size on the spatial resolution of phantom images acquired using a UHRCT system. A phantom designed to evaluate the high-contrast resolution was scanned. The scan data were reconstructed into four types of UHRCT image series consisting of the following possible combinations: two types of reconstruction kernels on the filtered back-projection method (for the lung and mediastinum) and two types of matrix sizes (1024² and 2048²). These images were displayed under eight types of display conditions: three image sizes displayed on a 2-megapixel (MP) and 3-MP color LCD and two image sizes on an 8-MP color LCD. A total of 32 samples (four image series × eight display conditions) were evaluated by eight observers for high-contrast resolution. The high-contrast resolution of the displayed UHRCT images was significantly affected by the displayed image size, although the largest (full-screen) displayed image size did not necessarily show the maximum high-contrast resolution. When the images were displayed in the full-screen size, LCD resolution affected the high-contrast resolution of only the 2048²-matrix-size images reconstructed using the lung kernel. In conclusion, the spatial resolution of UHRCT images may be affected by LCD resolution and displayed image size. To optimize the clinical display conditions for UHRCT images, it is necessary to adopt an LCD with an adequate resolution for each viewing situation.

Ultrahigh-Resolution Computed Tomography Improves Preoperative Computed Tomography Angiography for Deep Inferior Epigastric Artery Perforator Flap Reconstruction

OBJECTIVE

The aim of the study was to compare computed tomography (CT) angiography (CTA) imaging of deep inferior epigastric artery perforator (DIEP) using the ultrahigh-resolution CT (UHRCT) and conventional multidetector CT (MDCT).

METHODS

This retrospective study enrolled 20 patients who underwent CTA of DIEP flap with UHRCT and MDCT. Computed tomography values were measured at 4 large vessels (thoracic aorta, abdominal aorta, common iliac artery, and external iliac artery) and 5 peripheral vessels (proximal and distal internal thoracic artery, proximal and distal deep inferior epigastric artery, and DIEP).

RESULTS

There were no significant differences in mean CT values of the major vessel between UHRCT and MDCT. Ultrahigh-resolution CT shows higher CT values of the peripheral vessels than MDCT (P < 0.05 for all). The median CT values of the DIEP in UHRCT were approximately 3 times higher than those in MDCT (P < 0.001).

CONCLUSIONS

Ultrahigh-resolution CT provides higher-quality CTA of DIEP compared with MDCT.

Image quality improvement with deep learning-based reconstruction on abdominal ultrahigh-resolution CT: A phantom study

Purpose

In an ultrahigh‐resolution CT (U‐HRCT), deep learning‐based reconstruction (DLR) is expected to drastically reduce image noise without degrading spatial resolution. We assessed a new algorithm's effect on image quality at different radiation doses assuming an abdominal CT protocol.

Methods

For the normal‐sized abdominal models, a Catphan 600 was scanned by U‐HRCT with 100%, 50%, and 25% radiation doses. In all acquisitions, DLR was compared to model‐based iterative reconstruction (MBIR), filtered back projection (FBP), and hybrid iterative reconstruction (HIR). For the quantitative assessment, we compared image noise, which was defined as the standard deviation of the CT number, and spatial resolution among all reconstruction algorithms.

Results

Deep learning‐based reconstruction yielded lower image noise than FBP and HIR at each radiation dose. DLR yielded higher image noise than MBIR at the 100% and 50% radiation doses (100%, 50%, DLR: 15.4, 16.9 vs MBIR: 10.2, 15.6 Hounsfield units: HU). However, at the 25% radiation dose, the image noise in DLR was lower than that in MBIR (16.7 vs. 26.6 HU). The spatial frequency at 10% of the modulation transfer function (MTF) in DLR was 1.0 cycles/mm, slightly lower than that in MBIR (1.05 cycles/mm) at the 100% radiation dose. Even when the radiation dose decreased, the spatial frequency at 10% of the MTF of DLR did not change significantly (50% and 25% doses, 0.98 and 0.99 cycles/mm, respectively).

Conclusion

Deep learning‐based reconstruction performs more consistently at decreasing dose in abdominal ultrahigh‐resolution CT compared to all other commercially available reconstruction algorithms evaluated.

Semi-automatic vessel detection for challenging cases of peripheral arterial disease

OBJECTIVES

Manual or semi-automated segmentation of the lower extremity arterial tree in patients with Peripheral arterial disease (PAD) remains a notoriously difficult and time-consuming task. The complex manifestations of the disease, including discontinuities of the vascular flow channels, the presence of calcified atherosclerotic plaque in close vicinity to adjacent bone, and the presence of metal or other imaging artifacts currently preclude fully automated vessel identification. New machine learning techniques may alleviate this challenge, but require large and reasonably well segmented training data.

METHODS

We propose a novel semi-automatic vessel tracking approach for peripheral arteries to facilitate and accelerate the creation of annotated training data by expert cardiovascular radiologists or technologists, while limiting the number of necessary manual interactions, and reducing processing time. After automatically classifying blood vessels, bones, and other tissue, the relevant vessels are tracked and organized in a tree-like structure for further visualization.

RESULTS

We conducted a pilot (N = 9) and a clinical study (N = 24) in which we assess the accuracy and required time for our approach to achieve sufficient quality for clinical application, with our current clinically established workflow as the standard of reference. Our approach enabled expert physicians to readily identify all clinically relevant lower extremity arteries, even in problematic cases, with an average sensitivity of 92.9%, and an average specificity and overall accuracy of 99.9%.

CONCLUSIONS

Compared to the clinical workflow in our collaborating hospitals (28:40 ± 7:45 [mm:ss]), our approach (17:24 ± 6:44 [mm:ss]) is on average 11:16 [mm:ss] (39%) faster.

Diagnostic value of deep learning reconstruction for radiation dose reduction at abdominal ultra-high-resolution CT

OBJECTIVES

We evaluated lower dose (LD) hepatic dynamic ultra-high-resolution computed tomography (U-HRCT) images reconstructed with deep learning reconstruction (DLR), hybrid iterative reconstruction (hybrid-IR), or model-based IR (MBIR) in comparison with standard-dose (SD) U-HRCT images reconstructed with hybrid-IR as the reference standard to identify the method that allowed for the greatest radiation dose reduction while preserving the diagnostic value.

METHODS

Evaluated were 72 patients who had undergone hepatic dynamic U-HRCT; 36 were scanned with the standard radiation dose (SD group) and 36 with 70% of the SD (lower dose [LD] group). Hepatic arterial and equilibrium phase (HAP, EP) images were reconstructed with hybrid-IR in the SD group, and with hybrid-IR, MBIR, and DLR in the LD group. One radiologist recorded the standard deviation of attenuation in the paraspinal muscle as the image noise. The overall image quality was assessed by 3 other radiologists; they used a 5-point confidence scale ranging from 1 (unacceptable) to 5 (excellent). Superiority and equivalence with prespecified margins were assessed.

RESULTS

With respect to the image noise, in the HAP and EP, LD DLR and LD MBIR images were superior to SD hybrid-IR images; LD hybrid-IR images were neither superior nor equivalent to SD hybrid-IR images. With respect to the quality scores, only LD DLR images were superior to SD hybrid-IR images.

CONCLUSIONS

DLR preserved the quality of abdominal U-HRCT images even when scanned with a reduced radiation dose.

KEY POINTS

• Lower dose DLR images were superior to the standard-dose hybrid-IR images quantitatively and qualitatively at abdominal U-HRCT. • Neither hybrid-IR nor MBIR may allow for a radiation dose reduction at abdominal U-HRCT without compromising the image quality. • Because DLR allows for a reduction in the radiation dose and maintains the image quality even at the thinnest slice section, DLR should be applied to abdominal U-HRCT scans.

Measurement of stapes footplate thickness in otosclerosis by ultra-high-resolution computed tomography

BACKGROUND

Ultra-high-resolution computed tomography (U-HRCT) utilizes a 1024 × 1024 matrix with 0.25-mm section thickness, offering better spatial resolution than conventional multi-detector row CT to detect anatomic data for otologic surgery.

AIMS

We examined stapes footplate thickness using U-HRCT in relation to stapedotomy to predict the difficulty of the surgical procedure.

MATERIALS AND METHODS

Subjects were 12 otosclerosis patients and 25 controls who underwent diagnostic U-HRCT. A profile curve (Hounsfield units) was used to measure stapes footplate thickness along a perpendicular line across the stapes footplate in a plane parallel to the lateral semicircular canal.

RESULTS

Footplate thickness was smaller at the midpoint than just before the anterior crus and just after the posterior crus. Interobserver variability was lowest at the midpoint, where foot plate thickness was significantly greater in the affected ear in otosclerosis patients compared with controls (0.60 ± 0.09 mm vs 0.46 ± 0.04 mm; p < .001). Otosclerosis patients were detected using U-HRCT with a high area under the curve. Difficulty in the stapes opening procedure correlated with stapes footplate thickness.

CONCLUSIONS

Footplate thickness on U-HRCT correlated with temporal bone anatomy and corresponded to surgical difficulty. Significance: U-HRCT-derived anatomic data is useful for evaluating the stapes.

Deep learning reconstruction of drip-infusion cholangiography acquired with ultra-high-resolution computed tomography

PURPOSE

Deep learning reconstruction (DLR) introduces deep convolutional neural networks into the reconstruction flow. We examined the clinical applicability of drip-infusion cholangiography (DIC) acquired on an ultra-high-resolution CT (U-HRCT) scanner reconstructed with DLR in comparison to hybrid and model-based iterative reconstruction (hybrid-IR, MBIR).

METHODS

This retrospective, single-institution study included 30 patients seen between January 2018 and November 2019. A radiologist recorded the standard deviation of attenuation in the paraspinal muscle as the image noise and calculated the contrast-to-noise ratio (CNR) in the common bile duct. The overall visual image quality of the bile duct on thick-slab maximum intensity projections was assessed by two other radiologists and graded on a 5-point confidence scale ranging from 1 (not delineated) to 5 (clearly delineated). The difference among hybrid-IR, MBIR, and DLR images was compared.

RESULTS

The image noise was significantly lower on DLR than hybrid-IR and MBIR images and the CNR and the overall visual image quality of the bile duct were significantly higher on DLR than on hybrid-IR and MBIR images (all: p < 0.001).

CONCLUSION

DLR resulted in significant quantitative and qualitative improvement of DIC acquired with U-HRCT.

Multi-Scale deep learning framework for cochlea localization, segmentation and analysis on clinical ultra-high-resolution CT images

BACKGROUND AND OBJECTIVE

Performing patient-specific, pre-operative cochlea CT-based measurements could be helpful to positively affect the outcome of cochlear surgery in terms of intracochlear trauma and loss of residual hearing. Therefore, we propose a method to automatically segment and measure the human cochlea in clinical ultra-high-resolution (UHR) CT images, and investigate differences in cochlea size for personalized implant planning.

METHODS

123 temporal bone CT scans were acquired with two UHR-CT scanners, and used to develop and validate a deep learning-based system for automated cochlea segmentation and measurement. The segmentation algorithm is composed of two major steps (detection and pixel-wise classification) in cascade, and aims at combining the results of a multi-scale computer-aided detection scheme with a U-Net-like architecture for pixelwise classification. The segmentation results were used as an input to the measurement algorithm, which provides automatic cochlear measurements (volume, basal diameter, and cochlear duct length (CDL)) through the combined use of convolutional neural networks and thinning algorithms. Automatic segmentation was validated against manual annotation, by the means of Dice similarity, Boundary-F1 (BF) score, and maximum and average Hausdorff distances, while measurement errors were calculated between the automatic results and the corresponding manually obtained ground truth on a per-patient basis. Finally, the developed system was used to investigate the differences in cochlea size within our patient cohort, to relate the measurement errors to the actual variation in cochlear size across different patients.

RESULTS

Automatic segmentation resulted in a Dice of 0.90 ± 0.03, BF score of 0.95 ± 0.03, and maximum and average Hausdorff distance of 3.05 ± 0.39 and 0.32 ± 0.07 against manual annotation. Automatic cochlear measurements resulted in errors of 8.4% (volume), 5.5% (CDL), 7.8% (basal diameter). The cochlea size varied broadly, ranging between 0.10 and 0.28 ml (volume), 1.3 and 2.5 mm (basal diameter), and 27.7 and 40.1 mm (CDL).

CONCLUSIONS

The proposed algorithm could successfully segment and analyze the cochlea on UHR-CT images, resulting in accurate measurements of cochlear anatomy. Given the wide variation in cochlear size found in our patient cohort, it may find application as a pre-operative tool in cochlear implant surgery, potentially helping elaborate personalized treatment strategies based on patient-specific, image-based anatomical measurements.

Automatic bronchial segmentation on ultra-HRCT scans: advantage of the 1024-matrix size with 0.25-mm slice thickness reconstruction

PURPOSE

The aim of this study was to evaluate the advantages of ultra-high-resolution computed tomography (U-HRCT) for automatic bronchial segmentation.

MATERIALS AND METHODS

This retrospective study was approved by the Institutional Review Board, and written informed consent was waived. Thirty-three consecutive patients who underwent chest CT by a U-HRCT scanner were enrolled. In each patient, CT data were reconstructed by two different protocols: 512 × 512 matrix with 0.5-mm slice thickness (conventional HRCT mode) and 1024 × 1024 matrix with 0.25-mm slice thickness (U-HRCT mode). We used a research workstation to compare the two CT modes with regard to the numbers and total lengths of the automatically segmented bronchi.

RESULTS

Significantly greater numbers and longer lengths of peripheral bronchi were segmented in the U-HRCT mode than in the conventional HRCT mode (P < 0.001, for fifth- to eighth-generation bronchi). For example, the mean numbers and total lengths of the sixth-generation bronchi were 81 and 1048 mm in the U-HRCT mode and 59 and 538 mm in the conventional HRCT mode.

CONCLUSIONS

The U-HRCT mode greatly improves automatic airway segmentation for the more peripheral bronchi, compared with the conventional HRCT mode. This advantage can be applied to routine clinical care, such as virtual bronchoscopy and automatic lung segmentation.

Updates in Vascular Computed Tomography

Computed tomography angiography (CTA) has become a mainstay for the imaging of vascular diseases, because of high accuracy, availability, and rapid turnaround time. High-quality CTA images can now be routinely obtained with high isotropic spatial resolution and temporal resolution. Advances in CTA have focused on improving the image quality, increasing the acquisition speed, eliminating artifacts, and reducing the doses of radiation and iodinated contrast media. Dual-energy computed tomography provides material composition capabilities that can be used for characterizing lesions, optimizing contrast, decreasing artifact, and reducing radiation dose. Deep learning techniques can be used for classification, segmentation, quantification, and image enhancement.

Ultra high-resolution computed tomography with 1024-matrix: Comparison with 512-matrix for the evaluation of pulmonary nodules

PURPOSE

To determine whether a 1024-matrix provides superior image quality for the evaluation of pulmonary nodules.

MATERIALS AND METHODS

Prospective evaluation conducted between December 2017 and April 2018, during which CT images showing lung nodules of more than 6 mm and less than 30 mmm were reconstructed with 2 different protocols: 0.5-mm thickness, 512 × 512 matrix, 34.5-cm field of view (FOV) (0.5-512 protocol); and 2-mm thickness, 1024 × 1024 matrix, 34.5-cm FOV (2-1024 protocol). Lung nodule characteristics such as margin, lobulation, pleural indentation, spiculation as well as peripheral vessels and bronchioles visibility and overall image quality were evaluated by three chest radiologists, using a 5-point scale. Image noise was evaluated by measuring the standard deviation in the region of interest for each image.

RESULTS

A total of 89 nodules were evaluated. The 2-1024 protocol performed significantly better for the subjective evaluation of pulmonary nodules (p = 0.006 ∼ p < 0.0001). However, image noise was significantly higher both subjectively and objectively (p = 0.036, p < 0.0001).

CONCLUSION

The use of a 2-1024 protocol does not increase the amount of images and allows better assessment of pulmonary nodules, despite noise increase.

Quantitative Analysis of Lower Leg Muscle Enhancement Measured From Dynamic Computed Tomographic Angiography for Diagnosis of Peripheral Arterial Occlusive Disease

OBJECTIVES

The purpose of this study was to evaluate whether quantitative analysis of lower leg muscle enhancement measured from dynamic computed tomographic angiography (dyn-CTA) could be used for diagnosis of peripheral arterial occlusive disease.

METHODS

Patients (N = 35) with known peripheral arterial occlusive disease underwent the dyn-CTA of calves first. Five minutes later, standard CTA of the peripheral runoff from the diaphragm to the toes was performed. A runoff score was assigned by radiologists as a reference standard for each of 4 lower leg artery segments. The lower leg muscle enhancement measured from the dyn-CTA was analyzed by using quantitative kinetic parameters, including initial enhancement (E1), peak enhancement (Epeak), and enhancement ratio (ER) calculated from average time attenuation curves. In addition, histogram of lower leg muscle enhancement was evaluated by using the first enhanced phase images.

RESULTS

Lower extremities were diagnosed as a normal group (n = 22) with each vessel segment score equals to 1 or lower and runoff score, 7 or lower, and otherwise as an ischemia group (n = 48). Average ± SD E1 is 91.4% ± 8.5% and 82.3% ± 10.7%, Epeak is 122.7% ± 10.4% and 115.6% ± 11.1%, and ER is 0.75 ± 0.05 and 0.72 ± 0.09 for normal and ischemia group, respectively. Statistical analysis showed that average E1 and Epeak for the ischemia group were significantly lower (P < 0.05) than the normal group. The histogram analysis demonstrated that mean and median of muscle enhancement in the ischemia group were significantly smaller (P < 0.05), and coefficient of variation (CV) was significantly larger (P < 0.05) than the normal group. There were weak negative correlations (r = -0.42, P < 0.05) between runoff scores and E1 and Epeak, and weak positive correlation (r = 0.40, P < 0.05) between runoff scores and CV. The receiver operating characteristics analysis between the 2 groups had area under the curve of 0.77 and 0.76 for E1 and CV, respectively.

CONCLUSIONS

Lower leg muscle enhancement measured from the dyn-CTA could be assessed quantitatively to assist diagnosis of ischemia in clinical practice.

The Role of Vascular Smooth Muscle Cells in Arterial Remodeling: Focus on Calcification-Related Processes

Arterial remodeling refers to the structural and functional changes of the vessel wall that occur in response to disease, injury, or aging. Vascular smooth muscle cells (VSMC) play a pivotal role in regulating the remodeling processes of the vessel wall. Phenotypic switching of VSMC involves oxidative stress-induced extracellular vesicle release, driving calcification processes. The VSMC phenotype is relevant to plaque initiation, development and stability, whereas, in the media, the VSMC phenotype is important in maintaining tissue elasticity, wall stress homeostasis and vessel stiffness. Clinically, assessment of arterial remodeling is a challenge; particularly distinguishing intimal and medial involvement, and their contributions to vessel wall remodeling. The limitations pertain to imaging resolution and sensitivity, so methodological development is focused on improving those. Moreover, the integration of data across the microscopic (i.e., cell-tissue) and macroscopic (i.e., vessel-system) scale for correct interpretation is innately challenging, because of the multiple biophysical and biochemical factors involved. In the present review, we describe the arterial remodeling processes that govern arterial stiffening, atherosclerosis and calcification, with a particular focus on VSMC phenotypic switching. Additionally, we review clinically applicable methodologies to assess arterial remodeling and the latest developments in these, seeking to unravel the ubiquitous corroborator of vascular pathology that calcification appears to be.

Quantitative Emphysema Measurement On Ultra-High-Resolution CT Scans

Purpose

To evaluate the advantages of ultra-high-resolution computed tomography (U-HRCT) scans for the quantitative measurement of emphysematous lesions over conventional HRCT scans.

Materials and methods

This study included 32 smokers under routine clinical care who underwent chest CT performed by a U-HRCT scanner. Chronic obstructive pulmonary disease (COPD) was diagnosed in 13 of the 32 participants. Scan data were reconstructed by 2 different protocols: i) U-HRCT mode with a 1024×1024 matrix and 0.25-mm slice thickness and ii) conventional HRCT mode with a 512×512 matrix and 0.5-mm slice thickness. On both types of scans, lesions of emphysema were quantitatively assessed as percentage of low attenuation volume (LAV%, <-950 Hounsfield units). LAV% values determined for scan data from the U-HRCT and conventional HRCT modes were compared by the Wilcoxon matched-pairs signed rank test. The association between LAV% and forced expiratory volume in 1 s per forced vital capacity (FEV₁/FVC) was assessed by the Spearman rank correlation test.

Results

Mean values for LAV% determined for the U-HRCT and conventional HRCT modes were 8.9 ± 8.8% and 7.3 ± 8.4%, respectively (P<0.0001). The correlation coefficients for LAV% and FEV₁/FVC on the U-HRCT and conventional HRCT modes were 0.50 and 0.49, respectively (both P<0.01).

Conclusion

Compared with conventional HRCT scans, U-HRCT scans reveal emphysematous lesions in greater detail, and provide slightly increased correlation with airflow limitation.

Peripheral artery disease: the new frontiers of imaging techniques to evaluate the evolution of regenerative medicine

Introduction: Stem cells (ESC, iPSC, MSC) are known to have intrinsic regenerative properties. In the last decades numerous findings have favored the development of innovative therapeutic protocols based on the use of stem cells (Regenerative Medicine/Cell Therapy) for the treatment of numerous diseases including PAD, with promising results in preclinical studies. So far, several clinical studies have shown a general improvement of the patient's clinical outcome, however they possess many critical issues caused by the non-randomized design of the limited number of patients examined, the type cells to be used, their dosage, the short duration of treatment and also their delivery strategy. Areas covered: In this context, the use of the most advanced molecular imaging techniques will allow the visualization of very important physio-pathological processes otherwise invisible with conventional techniques, such as angiogenesis, also providing important structural and functional data. Expert opinion: The new frontier of cell therapy applied to PAD, potentially able to stop or even the process that causes the disease, with particular emphasis on the clinical aspects that different types of cells involve and on the use of more innovative molecular imaging techniques now available.

Deep learning reconstruction improves image quality of abdominal ultra-high-resolution CT

OBJECTIVES

Deep learning reconstruction (DLR) is a new reconstruction method; it introduces deep convolutional neural networks into the reconstruction flow. This study was conducted in order to examine the clinical applicability of abdominal ultra-high-resolution CT (U-HRCT) exams reconstructed with a new DLR in comparison to hybrid and model-based iterative reconstruction (hybrid-IR, MBIR).

METHODS

Our retrospective study included 46 patients seen between December 2017 and April 2018. A radiologist recorded the standard deviation of attenuation in the paraspinal muscle as the image noise and calculated the contrast-to-noise ratio (CNR) for the aorta, portal vein, and liver. The overall image quality was assessed by two other radiologists and graded on a 5-point confidence scale ranging from 1 (unacceptable) to 5 (excellent). The difference between CT images subjected to hybrid-IR, MBIR, and DLR was compared.

RESULTS

The image noise was significantly lower and the CNR was significantly higher on DLR than hybrid-IR and MBIR images (p < 0.01). DLR images received the highest and MBIR images the lowest scores for overall image quality.

CONCLUSIONS

DLR improved the quality of abdominal U-HRCT images.

KEY POINTS

• The potential degradation due to increased noise may prevent implementation of ultra-high-resolution CT in the abdomen. • Image noise and overall image quality for hepatic ultra-high-resolution CT images improved with deep learning reconstruction as compared to hybrid- and model-based iterative reconstruction.