Do the cardiovascular risk profile and the degree of arterial wall calcification influence the performance of MDCT angiography of lower extremity arteries?

Combined influence of quantum iterative reconstruction level and kernel sharpness on image quality in photon counting CT angiography of the upper leg

Aim was to evaluate the influence of different quantum iterative reconstruction (QIR) levels on the image quality of femoral photon-counting CT angiographies (PCD-CTA).Ultra-high resolution PCD-CTA were obtained from both extremities of five extracorporeally-perfused cadavers using constant tube voltage and maximum radiation dose (71.2 ± 11.0 mGy). Images were reconstructed with three kernels (Bv48, Bv60, Bv76) and the four available levels of QIR. Signal attenuation in the arterial lumen, muscle, and fat were measured. Contrast-to-noise ratios (CNR) and blurring scores were calculated for objective assessment. Six radiologists evaluated the subjective image quality using a pairwise comparison tool.Higher QIR level resulted in a decisive image noise reduction, especially with sharper convolution kernels (Bv60: Q1 11.5 ± 6.3 HU vs. Q4 8.4 ± 2.6 HU; p < 0.001). Largest improvement of CNR was recorded with ultra-sharp reconstructions (Bv76: Q1 20.2 ± 4.4 vs. Q4 28.0 ± 3.5; p < 0.001). Blurring decreased with higher QIR levels for soft Bv48, remained constant for medium Bv60, and increased for sharp Bv76 reconstructions. Subjective QIR level preference varied kernel depending, preferred combinations were: Bv48/Q4, Bv60/Q2, Bv76/Q3. Interrater agreement was excellent.Sharp kernels benefited most from noise reduction of higher QIR levels in lower extremity PCD-CTA. In sum, QIR level 3 provided the best objective and subjective image quality results.

In vitro and in vivo optimized reconstruction for low-keV virtual monoenergetic photon-counting detector CT angiography of lower legs

BACKGROUND

Lower extremity peripheral artery disease frequently presents with calcifications which reduces the accuracy of computed tomography (CT) angiography, especially below-the-knee. Photon-counting detector (PCD)-CT offers improved spatial resolution and less calcium blooming. We aimed to identify the optimal reconstruction parameters for PCD-CT angiography of the lower legs.

METHODS

Tubes with different diameters (1-5 mm) were filled with different iodine concentrations and scanned in a water container. Images were reconstructed with 0.4 mm isotropic resolution using a quantitative kernel at all available sharpness levels (Qr36 to Qr76) and using different levels of quantum iterative reconstruction (QIR-2-4). Noise and image sharpness were determined for all reconstructions. Additionally, CT angiograms of 20 patients, reconstructed with a medium (Qr44), sharp (Qr60), and ultrasharp (Qr72) kernel at QIR-2-4, were evaluated by three readers assessing noise, delineation of plaques and vessel walls, and overall quality.

RESULTS

In the phantom study, increased kernel sharpness led to higher image noise (e.g., 16, 38, 77 HU for Qr44, Qr60, Qr72, and QIR-3). Image sharpness increased with increasing kernel sharpness, reaching a plateau at the medium-high level 60. Higher QIR levels decreased image noise (e.g., 51, 38, 25 HU at QIR-2-4 and Qr60) without reducing vessel sharpness. The qualitative in vivo results confirmed these findings: the sharp kernel (Qr60) with the highest QIR yielded the best overall quality.

CONCLUSION

The combination of a sharpness level optimized reconstruction kernel (Qr60) and the highest QIR level yield the best image quality for PCD-CT angiography of the lower legs when reconstructed at 0.4-mm resolution.

RELEVANCE STATEMENT

Using high-resolution PCD-CT angiography with optimized reconstruction parameters might improve diagnostic accuracy and confidence in peripheral artery disease of the lower legs.

KEY POINTS

Effective exploitation of the potential of PCD-CT angiography requires optimized reconstruction parameters. Too soft or too sharp reconstruction kernels reduce image quality. The highest level of quantum iterative reconstruction provides the best image quality.

CT angiography of the lower limbs: combining small field of view with large matrix size and iterative reconstruction further improves image quality of below-the-knee arteries

BACKGROUND

Image quality and diagnostic accuracy in computed tomography angiography (CTA) reach their limits in imaging of below-the-knee vessels.

PURPOSE

To evaluate whether image quality in CTA of lower limbs is further improvable by combining side-separate reconstruction with a larger matrix size and whether resulting noise can be compromised with iterative reconstruction (IR).

MATERIAL AND METHODS

From CTA of the lower extremities of 26 patients (5 women, 21 men; mean age = 68.5 ± 10.3 years), the lower legs were reconstructed side-separately with different reconstruction algorithms and matrix sizes including filtered back projection (FBP) with a 512 × 512 matrix, FBP with a 1024 × 1024 matrix, IR (SAFIRE) with a 512 × 512 matrix, and IR (SAFIRE) with a 1024 × 1024 matrix. A total of 208 CT series were evaluated. Subjective image quality was assessed by two readers using a 5-point Likert scale. Image noise was assessed by measuring signal-to-noise and contrast-to-noise ratios.

RESULTS

Subjective image quality was rated significantly higher when using a 1024 × 1024 matrix (P < 0.001) and could further be increased with IR. Vessel sharpness was rated significantly better with a larger matrix (P < 0.001). Visible and measured image noise was significantly higher with a 1024 × 1024 matrix but could be reduced by using IR (P < 0.001), even to a level below FBP with a 512 × 512 matrix while reconstructing with a larger matrix (P < 0.001).

CONCLUSION

Image quality, image noise, and vessel sharpness can be further improved in CTA of the lower extremities with side-separate reconstruction using a 1024 × 1024 matrix size and IR.

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.

Automatic Plaque Removal Using Dual-Energy Computed Tomography Angiography: Diagnostic Accuracy and Utility in Patients with Peripheral Artery Disease

Background and Objectives: This study aimed to evaluate the utility and accuracy of dual-energy automatic plaque removal (DE-APR) in patients with symptomatic peripheral arterial disease (PAD) using digital subtraction angiography (DSA) as the reference standard. Materials and Methods: We retrospectively analyzed 100 patients with PAD who underwent DE computed tomography angiography (DE-CTA) and DSA of the lower extremities. DE-CTA was used to generate APR subtracted images. In the three main arterial segments (aorto-iliac segment, femoro-popliteal segment, and below-the-knee segment), the presence or absence of hemodynamically significant stenosis (>50%) and calcification was assessed using the images. CTA data were analyzed using different imaging approaches (DE-standard reconstruction image (DE-SR), DE-APR maximum intensity projection image (APR), and DE-SR with APR). Results: For all segments evaluated, the sensitivity, specificity, and accuracy for detecting significant stenosis were 98.16%, 81.01%, and 89.58%, respectively, with DE-SR; 97.79%, 83.33%, and 90.56%, respectively, with APR; and 98.16%, 92.25%, and 95.20%, respectively, with DE-SR with APR. DE-SR with APR had greater accuracy than DE-SR or APR alone (p < 0.001 and p < 0.001, respectively). When analyzed based on vascular wall calcification, the accuracy of DE-SR with APR remained greater than 90% regardless of calcification severity, whereas DE-SR showed a considerable reduction in accuracy in moderate to severe calcification. In the case of APR, the degree of vascular wall calcification did not significantly influence the accuracy in the aorto-iliac and femoro-popliteal segments. DE-SR with APR achieved significantly higher diagnostic accuracy for all lower extremity segments in evaluating hemodynamically significant stenosis in patients with symptomatic PAD and transcended the impact of vascular wall calcification compared with DE-SR. Conclusions: APR demonstrated favorable diagnostic performance in the aorto-iliac and femoro-popliteal segments, exhibiting good agreement with DSA even in cases of moderate to severe vascular wall calcification.

The impact of the field of view (FOV) on image quality in MDCT angiography of the lower extremities

Objectives

To evaluate the impact of the reconstructed field-of-view (FOV) on image quality in computed-tomography angiography (CTA) of the lower extremities.

Methods

A total of 100 CTA examinations of the lower extremities were acquired on a 2 × 192-slice multidetector CT (MDCT) scanner. Three different datasets were reconstructed covering both legs (standard FOV size) as well as each leg separately (reduced FOV size). The subjective image quality was evaluated for the different vessel segments (femoral, popliteal, crural, pedal) by three readers using a semi-quantitative Likert scale. Additionally, objective image quality was assessed using an automated image quality metric on a per-slice basis.

Results

The subjective assessment of the image quality showed an almost perfect interrater agreement. The image quality of the small FOV datasets was rated significantly higher as compared to the large datasets for all patients and vessel segments (p < 0.05) with a tendency towards a higher effect in smaller vessels. The difference of the mean scores between the group with the large FOV and small FOV was 0.68 for the femoral level, 0.83 for the popliteal level, 1.12 for the crural level, and 1.08 for the pedal level. The objective image quality metric also demonstrated a significant improvement of image quality in the small FOV datasets.

Conclusions

Side-separated reconstruction of each leg in CTA of the lower extremities using a small reconstruction FOV significantly improves image quality as compared to a standard reconstruction with a large FOV covering both legs.

Key Points

• In CT angiography of the lower legs, the side-separated reconstruction of each leg using a small field-of-views improves image quality as compared to a standard reconstruction covering both legs.

• The side-separated reconstruction can be readily implemented at every commercially available CT scanner.

• There is no need for additional hardware or software and no additional burden to the patient.

Lower extremity CT angiography in peripheral arterial disease: from the established approach to evolving technical developments

With the advent of multidetector computed tomography (CT), CT angiography (CTA) has gained widespread popularity for noninvasive imaging of the arterial vasculature. Peripheral extremity CTA can nowadays be performed rapidly with high spatial resolution and a decreased amount of both intravenous contrast and radiation exposure. In patients with peripheral artery disease (PAD), this technique can be used to delineate the bilateral lower extremity arterial tree and to determine the amount of atherosclerotic disease while differentiating between acute and chronic changes. This article provides an overview of several imaging techniques for PAD, specifically discusses the use of peripheral extremity CTA in patients with PAD, clinical indications, established technical considerations and novel technical developments, and the effect of postprocessing imaging techniques and structured reporting.

Effects of epinephrine on heart rate variability and cytokines in a rat sepsis model

Catecholamines have both anti-inflammatory and vasoactive properties. A decreased cardiac response to catecholamines has been associated with a high risk of death in sepsis and septic shock. The aim of this study was to investigate the effects of epinephrine (EPI) on heart rate variability (HRV) and autonomic balance, as well as cytokine levels, in a rat sepsis model. Thirty-six male Sprague-Dawley rats were assigned to 4 experimental groups and 2 control groups of 6 rats each. The rats in the experimental groups were inoculated with a lipopolysaccharide (LPS, endotoxin) to establish a sepsis model. Group A received only LPS; group B received LPS, antecedent EPI and the nonselective β-blocker propranolol; group C received LPS and antecedent EPI; and group D received LPS, antecedent EPI and the selective β1-blocker esmolol. One control group received EPI and the other received saline placebo. Heart rate variability (HRV) was analyzed and tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6) and interleukin-1β (IL-1β) levels were measured. Measurements were carried out at baseline, at 0 hour after EPI infusion, and at 0.5, 2, and 4 hours after LPS inoculation. There were significant differences in HRV and cytokine levels between the groups, indicating that LPS infusion caused autonomic imbalance. Antecedent EPI significantly decreased the level of TNF-α in group C compared with group A in which TNF-α level peaked at 2 hours and then declined. Propranolol (group B) but not esmolol (group D) administration resulted in elevated TNF-α levels, comparable to those observed in group A. In conclusion, antecedent administration of EPI in a rat sepsis model inhibits the production of TNF-α possibly via the β2-adrenoceptor.

Peripheral arterial disease screening and diagnostic practice: A scoping review

Early reliable, valid screening, diagnosis, and treatment improve peripheral arterial disease outcomes, yet screening and diagnostic practices vary across settings and specialties. A scoping literature review described reliability and validity of peripheral ischaemia diagnosis or screening tools. Clinical studies in the PUBMED database January 1, 1970, to August 13, 2018, were reviewed summarising ranges of reliability and validity of peripheral ischaemia diagnostic and screening tools for patients with non-neuropathic lower leg ischaemia. Peripheral ischaemia screening and diagnostic practices varied in parameters measured such as timing, frequency, setting, ordering clinicians, degree of invasiveness, costs, definitions, and cut-off points informing clinical and referral decisions. Traditional ankle/brachial systolic blood pressure index <0.9 was a reliable, valid lower leg ischaemia screening test to trigger specialist referral for detailed diagnosis. For patients with advanced peripheral ischaemia or calcified arteries, toe-brachial index, claudication, or invasive angiographic imaging techniques that can have complications were reliable, valid screening, and diagnostic tools to inform management decisions. Ankle/brachial index testing is sufficiently reliable and valid for use during routine examinations to improve timing and consistency of peripheral ischaemia screening, triggering prompt specialist referral for more reliable, accurate Doppler, or other diagnosis to inform treatment decisions.

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

Despite advances, challenges remain for less invasive imaging of peripheral arterial occlusive disease (PAOD) using computed tomography (CT) angiography. The application of dual-energy imaging to PAOD has been reported to improve the diagnostic accuracy of this application; however, severe arteriosclerosis with heavy arterial wall calcification still hampers definitive lesion characterisation, especially in distal and smaller arteries. Recently an ultra-high resolution scanner has been introduced. In combination with advances in post-processing, such as subtraction techniques, these developments may overcome some of the current challenges and allow far more detailed characterisation of PAOD non-invasively. The aim of this review is to describe our current experience with ultra-high resolution CT in combination with subtraction and discuss the potential advantages of their application for peripheral angiography.

Combined Static and Dynamic Computed Tomography Angiography of Peripheral Artery Occlusive Disease: Comparison with Magnetic Resonance Angiography

PURPOSE

To compare in patients with known peripheral artery occlusive disease (PAOD), image quality of a combined CTA to a combined MRA protocol, including both static and dynamic acquisitions.

MATERIALS AND METHODS

Twenty-two patients with PAOD were examined with a combined CTA and MRA protocol consisting of static acquisitions (s-CTA, s-MRA) of the entire runoff and dynamic acquisitions (d-CTA, d-MRA) of the calves. Two radiologists compared image quality of the s-MRA versus s-CTA as well as d-MRA versus d-CTA. Image quality was assessed on a segmental basis using a 4-point Likert scale.

RESULTS

For s-CTA, 76% of segments were rated as excellent or good. For s-MRA, 50% of segments were rated as excellent or good (p < 0.0001). For d-CTA, median image quality score for all segments was rated as excellent for both readers. For d-MRA, median image quality for the different segments ranged from moderate to good. For both d-CTA and d-MRA, the median image quality scores were significantly higher for all segments of the lower limb compared with the static examinations of the lower limb segments (all p values < 0.0001). In patients with PAOD category 4-6, 80% of segments were rated as excellent or good for d-CTA, while 45% of segments were rated as poor or non-diagnostic for d-MRA.

CONCLUSION

In patients with known PAOD, a combined static and dynamic CTA examination improves image quality relative to static and dynamic MRA and should be considered as an alternative to MRA, particularly in patients with advanced stage PAOD.

Diagnostic confidence of run-off CT-angiography as the primary diagnostic imaging modality in patients presenting with acute or chronic peripheral arterial disease

Objectives

To investigate the reliability of CT-angiography of the lower extremities (run-off CTA) to derive a treatment decision in patients with acute and chronic peripheral artery disease (PAD).

Materials and Methods

314 patients referred for run-off CTA were includ-ed in this retrospective study. First, diagnostic confidence of run-off CTA to derive a treat-ment decision was assessed in an interdisciplinary vascular conference using a 2 point scale (sufficient or not sufficient diagnostic confidence) and compared with the image quality eval-uated by two readers in consensus in four different levels (abdominopelvic, thigh, calf, foot arteries). Second, reliability of treatment decision was verified in all patients undergoing re-vascularization therapy.

Results

Diagnostic confidence of run-off CTA to derive a treatment deci-sion was sufficient in all patients with acute and in 97% of patients (215/221) with chronic PAD, whereas the rate of run-off CTA with non-diagnostic image quality was considerably higher in the calf and foot level (acute vs. chronic; calf: 28% vs.17%; foot: 52% vs. 20%). Reliability of treatment decision was superior for patients with chronic (123/133 = 92%) than for patients with acute PAD (64/78 = 82%, P = 0.02).

Conclusion

Run-off CTA is a reliable imaging modality for primary diag-nostic work-up of patients with acute and chronic PAD.

Chronic critical limb ischemia

BACKGROUND

Some 40 000 lower limb amputations are performed in Germany each year, 70% of them in diabetics. About 80% of all major amputations may be preventable with the use of new interventional and vascular surgical procedures, particularly on the arteries of the leg and foot. We present the current state of the art in revascularization techniques and evaluate their usefulness for preservation of the lower limb.

METHODS

This overview is based on the guidelines for the diagnosis and treatment of peripheral artery disease (PAD) and diabetic foot syndrome (DFS) that have been issued by the American Heart Association (AHA), the American College of Cardiology (ACC), the German Society of Angiology (DGA), the Trans-Atlantic Intersociety Consensus (TASC II), the German Society of Vascular Surgery (DGG), and the German Diabetes Society (DDG). A selective search in PubMed for relevant articles that appeared from 2000 to 2011 was conducted with the search terms "pedal bypass," "vascular intervention crural pedal," and "crural-pedal revascularization."

RESULTS

Most of the data on crural and pedal revascularization are derived from small-scale studies. The few comparative studies of interventional treatments and bypass surgery have not revealed any significant differences in outcome, but all studies of revascularization have shown good success rates for lower limb preservation.

CONCLUSION

Though the data are still sparse, the high reported rates of limb preservation imply that peripheral revascularization techniques can play a major role in the treatment of chronic critical limb ischemia (CLI). Therefore, these techniques are recommended without exception by the current guidelines.

Characteristics of peripheral arterial disease and its relevance to the diabetic population

Peripheral arterial disease (PAD) is very frequent in diabetics, and it increases with age. Foot examination contributes poorly to diagnosis of PAD. The ankle-brachial index (ABI) measurement is considered the most accurate noninvasive diagnostic method when evaluating PAD: ABI evaluation is recommended in all diabetics aged >50 years. Many diabetic patients with PAD have a concomitant sensitive neuropathy: as a consequence, perception of ischemic pain is remarkably reduced or completely blocked. The result is that the prevalence of claudication in the diabetic population with PAD is lower than the prevalence of critical limb ischemia (CLI) in this population. CLI is a major risk factor for lower extremity amputation without revascularization. Ankle and toe pressures and oxygen tension at the foot are the noninvasive diagnostic parameters of CLI though the medial artery calcification inhibits accurate determination of the ankle and toe pressures, especially when a forefoot ulcer is present. In diabetics, the anatomical localization is mainly distal; arterial wall calcification is frequently observed and occlusion occurs more frequently than stenosis. Such anatomical features, along with the difficulties in the diagnostic approach, account for the fundamental role of CLI as the main prognostic indicator for major amputation. PAD is an expression of systemic atherosclerotic disease. Prognosis of patients with PAD is related to the presence and extent of underlying coronary artery disease (CAD) but also to the severity of PAD: in particular, patients in whom revascularization is not feasible have the highest mortality rate.

64-section CT angiography in patients with critical limb ischaemia and severe claudication: comparison with digital subtractive angiography

AIM

To assess the utility of 64 section multidetector computed tomography (MDCT) lower-limb angiography in the evaluation of patients with critical limb ischaemia (CLI) or severe intermittent claudication (IC) in grading disease before endovascular treatment.

MATERIALS AND METHODS

Forty-one consecutive patients with CLI or severe IC were assessed using 64 section MDCT angiography. The MDCT examinations were compared with subsequent intra-arterial digital subtraction angiography (IADSA) examinations performed at the time of endovascular intervention. The MDCT and IADSA examinations were independently scrutinized by readers blinded to the results of the other imaging method.

RESULTS

For arterial segments with haemodynamically significant disease (stenosis ≥50%), the overall sensitivity, specificity, and accuracy of MDCT in patients with severe claudication and CLI was 99% (95% CI: 98-100%), 98% (95% CI: 97-100%) and 98% (95% CI: 97-99%), respectively. The positive predictive value (PPV) was 97% and the negative predictive value (NPV) was 99%.

CONCLUSIONS

MDCT angiography is a useful tool in the assessment of patients with severe claudication and CLI and can be reliably used to grade disease severity and plan treatment.

Diabetes revealed: multisystem danger

OBJECTIVE

The purpose of this article is to review the role of diagnostic imaging in the evaluation of women with diabetes.

CONCLUSION

Diabetic patients present a challenging population for the performance of various imaging studies and special considerations need to be made to obtain adequate studies. Imaging plays a significant role in assessing the multisystem morbidity of diabetes. Furthermore, diabetes in women may have some unique features and consequences and imaging studies can aid in the correct management of these patients.