Carotid artery stenting and follow-up: value of 64-MSCT angiography as complementary imaging method to color-coded duplex sonography

Purpose

To compare 64-multi-slice-CT angiography (64-MSCTA) to color-coded duplex sonography (CCDS) in the follow-up after carotid artery stenting (CAS).

Methods

Thirty patients who had an MSCTA and CCDS examination prior and after CAS were included. Twelve closed-cell and 24 open-cell stents were implanted. Neointimal surface, in-stent-restenosis (ISR), stent expansion, and fracture were evaluated. In addition, the occurrence of atherosclerotic lesions leading to a > 50% stenosis in supraaortic vessels was assessed.

Results

With MSCTA, >50% ISR was found in 5.6% of cases during a mean follow-up of 41.7 months. Comparing MSCTA and CCDS, grading of ISR and absolute diameters of neointimal surface correlated moderately (Spearman = 0.402, p = 0.015; Pearson = 0.404, p = 0.03). Assessment of the neointimal surface was significantly better with MSCTA (100% vs. 80.6%; p = 0.011). Stent expansion was significant, compared to the basic value, with both modalities and stent types (p < 0.001). Of 237 additionally assessed vessel segments, a > 50% stenosis was detected in 38 (16.0%) vessel segments. Findings were stable in 25 (10.5%) and progressed in 11 (4.6%) vessel segments. Five small intracranial aneurysms were detected in four (13.3%) patients. Of 21 incidental findings in 16 (51.6%) patients there was one with malignancy (4.8%).

Conclusion

With regard to ISR and stent expansion, no significant difference was found, when MSCTA and CCDS were compared. CTA is quite applicable as a complementary imaging method for the follow-up of patients with carotid artery stents. Additional advantages are the detection of supraaortic vessel pathologies and incidental findings.     

Evaluation of carotid vessel wall enhancement with image subtraction after gadobenate dimeglumine-enhanced MR angiography

Objectives

This study was aimed at testing the value of image subtraction for evaluating carotid vessel wall enhancement in contrast-enhanced MR angiography (MRA).

Materials and methods

IRB approval was obtained. The scans of 81 consecutive patients who underwent carotid MRA with 0.1 mmol/kg of gadobenate dimeglumine were reviewed. Axial carotid 3D T1-weighted fast low-angle shot sequence before and 3 min after contrast injection were acquired and subtracted (enhanced minus unenhanced). Vessel wall enhancement was assigned a four-point score using native or subtracted images from 0 (no enhancement) to 3 (strong enhancement). Stenosis degree was graded according to NASCET.

Results

With native images, vessel wall enhancement was detected in 20/81 patients (25%) and in 20/161 carotids (12%), and scored 2.0 ± 0.6 (mean ± standard deviation); with subtracted images, in 21/81 (26%) and 22/161 (14%), and scored 2.5 ± 0.6, respectively (P < 0.001, Sign test). The overall stenosis degree distribution was: mild, 41/161 (25%); moderate, 77/161 (48%); severe, 43/161 (27%). Carotids with moderate stenosis showed vessel wall enhancement with a frequency (17/77, 22%) significantly higher than that observed in carotids with mild stenosis (1/41, 2%) (P = 0.005, Fisher exact test) and higher, even though with borderline significance (P = 0.078, Fisher exact test), than that observed in carotids with severe stenosis (4/43, 9%).

Conclusion

Roughly a quarter of patients undergoing carotid MRA showed vessel wall enhancement. Image subtraction improved vessel wall enhancement conspicuity. Vessel wall enhancement seems to be an event relatively independent from the degree of stenosis. Further studies are warranted to define the relation between vessel wall enhancement and histopathology, inflammatory status, and instability.     

A comparative analysis of double inversion recovery TFE and TSE sequences on carotid artery wall imaging

Objective

To analyze the characteristics of double inversion recovery (DIR) turbo field echo (TFE) and turbo spin echo (TSE) sequences and explore the value of double inversion recovery TFE sequence on carotid artery wall imaging.

Patients and methods

56 patients (32 males and 24 females, aged 31–76 years with a mean age of 53 years) were performed with DIR TFE and DIR TSE T1 weighted imaging (T1WI) sequences on carotid artery bifurcations. Image quality acquired by different techniques were evaluated and scored by two physicians. Whether there is significant difference is determined by SPSS 11.0 software. Paired-samples t test was used for statistics.

Results

There was no significant difference in the image quality scores between two sequences (t = 0.880, P = 0.383 > 0.05).

Conclusions

DIR TFE sequence has short scanning time and high spatial resolution. DIR TFE sequence can be used as the preferred sequence for screening carotid atherosclerotic plaque compared with DIR TSE sequence.     

Quantification of coronary stenosis by dual source computed tomography in patients: a comparative study with intravascular ultrasound and invasive angiography

Objective

To determine the accuracy of dual-source CT (DSCT) to quantify coronary stenosis compared to intravascular ultrasound (IVUS) and quantitative coronary angiography (QCA).

Methods

21 patients (23 vessels) were examined with DSCT, IVUS and invasive coronary angiography. Coronary minimal luminal diameter (MLD) and area (MLA) were measured in cross-sectional multi-planar reformatted images perpendicular to the vessel long-axis. The vessel cross-sectional area stenosis (MLA/CSA ratio) was calculated. DSCT results were compared with IVUS and QCA.

Results

A good correlation between DSCT and IVUS was noted for diameter and area stenosis (r = 0.69 and r = 0.73), with an overestimation of MLD stenosis by DSCT (+9.1%) and an underestimation of MLA stenosis (−5.8%). For MLD and MLA, high correlation coefficients (r = 0.78 and r = 0.90, respectively) were found between DSCT and IVUS; and the bias was almost zero (−0.41 mm and +0.1 mm², respectively).The correlation between DSCT and QCA was moderate (r = 0.60) for MLD stenosis with minor overestimation by DSCT (+4.0%) and moderate (r = 0.59) for MLD (bias, +0.01 mm).The cross-sectional area stenosis showed a moderate correlation (r = 0.59) between DSCT and IVUS (+0.00).

Conclusions

DSCT allows accurate quantification of coronary stenosis as compared to IVUS. An excellent correlation was found for the MLA between DSCT and IVUS.     

Assessment of coronary artery disease by post-mortem cardiac MR

Objectives

Minimally invasive or virtual autopsies are being advocated as alternative to traditional autopsy, but have limited abilities to detect coronary artery disease. It was the objective of this study to assess if the occurrence of chemical shift artifacts (CSA) along the coronary arteries on non-contrast, post-mortem cardiac MR may be used to investigate coronary artery disease.

Methods

We retrospectively compared autopsy and CT findings of 30 cases with significant (≥75%), insignificant (<75%), or absent coronary artery stenosis to post-mortem cardiac MR findings. The chi-square test was used to investigate if the occurrence of CSA depends on the presence or absence of stenosis. Sensitivity, specificity and predictive values were calculated for each finding.

Results

CSA indicates the absence of (significant) stenosis (p < 0.001). The occurrence of paired dark bands in lieu of CSA on post-mortem cardiac MR suggests (significant) coronary arteries stenosis (p < 0.001). Both findings have a high specificity but low sensitivity.

Conclusions

CSA is a marker of vessel patency. The presence of paired dark bands indicates stenosis. These criteria improve the ability of minimally invasive or virtual autopsy to detect coronary artery disease related deaths.     

Intraobserver and interobserver agreement of volume perfusion CT (VPCT) measurements in patients with lung lesions

Objectives

To evaluate intraobserver and interobserver agreement of manually encompassed lung lesions for perfusion measurements using volume-perfusion computed tomography (VPCT).

Materials and methods

Institutional review board approval and informed consent were obtained. HIPAA guidelines were followed. A 65-s dynamic study was acquired with scan parameters 80 kV, 60 mA s (80 mA s for patients ≥70 kg), 128 × 0.6 mm collimation. Blood flow (BF), blood volume (BV) and K^trans parameters were determined by syngo volume perfusion CT body with 88 lesions analyzed retrospectively.

Results

Within-subject coefficients of variation for intraobserver agreement (range 6.59–12.82%) were superior to those for interobserver agreement (range 21.75–38.30%). Size-dependent analysis revealed lower agreements for lesions <4 cm as compared to larger lesions. Additionally, agreements of the upper, middle and lower lung zones were different.

Conclusions

Intraobserver agreement was substantial for VPCT lung cancer perfusion measurements encouraging the use for tumor characterization and therapy response monitoring. Interobserver agreement is limited and unexperienced readers should be trained before using this new method.     

MDCT angiography for detection of pulmonary emboli: comparison between equi-iodine doses of iomeprol 400 mgI/mL and iodixanol 320 mgI/mL

Objectives

To compare iomeprol 400 and iodixanol 320 in pulmonary artery MDCTA in subjects with suspected pulmonary embolism.

Methods

Eighty randomized subjects received equi-iodine intravenous doses (48 g) of iomeprol 400 (n = 40) or iodixanol 320 (n = 40), via power injector at 4 mL/s. Four-row (35 subjects) and 64-row (45 subjects) scanners were used. Lumen attenuation was determined on-site and by two off-site blinded readers in the main, lobar, segmental and subsegmental pulmonary arteries. Statistical comparison between groups was performed for demographics and lumen attenuation.

Results

There were no between-group differences (p > 0.05) in demographics. Pulmonary artery attenuation was significantly (p ≤ 0.03) higher with iomeprol 400 for all readers. Attenuation quality was excellent in more patients after iomeprol 400 than after iodixanol-320 (80% vs. 62.5%; 82.5% vs. 77.5%; off-site readers 1 and 2, respectively). No safety concerns were noted.

Conclusion

The greater iodine delivery rate achievable with iomeprol 400 compared to iodixanol-320 at equi-iodine dose and injection rate permits consistently greater attenuation at all levels of the pulmonary arterial tree.     

Performance of unenhanced respiratory-gated 3D SSFP MRA to depict hepatic and visceral artery anatomy and variants

Objectives

To prospectively evaluate the performance of unenhanced respiratory-gated magnetization-prepared 3D-SSFP inversion recovery MRA (unenhanced-MRA) to depict hepatic and visceral artery anatomy and variants in comparison to contrast-enhanced dynamic gradient-echo MRI (CE-MRI) and to digital subtraction angiography (DSA).

Methods

Eighty-four patients (55.6 ± 12.4 years) were imaged with CE-MRI (TR/TE 3.5/1.7 ms, TI 1.7 ms, flip-angle 15°) and unenhanced-MRA (TR/TE 4.4/2.2 ms, TI 200 ms, flip-angle 90°). Two independent readers assessed image quality of hepatic and visceral arteries on a 4-point-scale. Vessel contrast was measured by a third reader. In 28 patients arterial anatomy was compared to DSA.

Results

Interobserver agreement regarding image quality was good for CE-MRI (κ = 0.77) and excellent for unenhanced-MRA (κ = 0.83). Unenhanced-MRA yielded diagnostic image quality in 71.6% of all vessels, whereas CE-MRI provided diagnostic image quality in 90.6% (p < 0.001). Vessel-based image quality was significantly superior for all vessels at CE-MRI compared to unenhanced-MRA (p < 0.01). Vessel contrast was similar among both sequences (p = 0.15). Compared to DSA, CE-MRI and unenhanced-MRA yielded equal accuracy of 92.9–96.4% for depiction of hepatic and visceral artery variants (p = 0.93).

Conclusions

Unenhanced-MRA provides diagnostic image quality in 72% of hepatic and visceral arteries with no significant difference in vessel contrast and similar accuracy to CE-MRI for depiction of hepatic and visceral anatomy.     

The prevalence and clinical predictors of incidental atherosclerotic renal artery stenosis

Objective

To evaluate the prevalence of incidental renal artery stenosis due to atherosclerosis and associated risk factors in patients with peripheral arterial disease (PAD).

Materials and methods

To determine renal artery stenosis, aortofemoropopliteal digital substraction angiographies (DSA) of 629 consecutive patients with PAD were prospectively reviewed. Angiographies were performed as catheter angiography with automated pump injection. Of the patients, 540 were male (86%) and 89 female (14%) (mean age ± S.D.: 61.5 ± 11.1 years). Statistical analysis was performed to determine the association of significant renal artery stenosis (≥60% diameter stenosis) with patient demographics (age, sex, reason for angiography and smoking status), medical history (diabetes mellitus, hypertension and coronary artery disease), laboratory values (blood creatinine, fasting glucose, triglycerides, LDL, HDL and total cholesterol) and distribution of PAD (aortoiliac, femoropopliteal and crural diseases and multisegment involvement).

Results

Renal artery disease was found in 33% (207 of 629) of all patients with peripheral arterial disease, and 9.6% of patients (n = 60) had significant (≥60%) renal artery stenosis. Only age and hypertension (blood pressure systolic >140 mmHg or diastolic >90 mmHg) were independent risk factors for significant renal artery stenosis on multivariate analysis. Mean age of patients with RAS was 66.5 ± 8.9 years compared with 61 ± 11.2 years for patients without RAS (p < 0.001). Hypertension was found in 41% of the patients in control group and in 63% of the patients in RAS group (p = 0.01).

Conclusion

Incidental renal artery stenosis which can be mild or significant is a relatively common finding among patients with peripheral arterial disease. Advance age and hypertension are closely associated with significant renal artery stenosis.     

Diagnostic image quality of a comprehensive high-pitch dual-spiral cardiothoracic CT protocol in patients with undifferentiated acute chest pain

Objective

To evaluate diagnostic image quality of high-pitch dual source comprehensive cardiothoracic CT protocol in patients presenting with acute undifferentiated chest pain.

Materials and methods

Consecutive symptomatic subjects (n = 51) with undifferentiated acute chest pain underwent ECG-synchronized high-pitch dual-spiral chest CT angiography (Definition Flash, Siemens Medical Solutions, 2 × 100 kVp or 2 × 120 kV if BMI > 30, collimation: 128 × 0.6 mm, pitch: 3.2). Independent investigators determined the image quality of each cardiac and pulmonary vessel segment, measured contrast-to-noise-ratio (CNR), and determined radiation exposure. In addition, the prevalence of CT findings (pulmonary embolism (PE), aortic dissection (AD) and significant coronary stenosis (≥50%)) was determined. Univariate and multivariate analysis were performed to determine the subpopulation with highest diagnostic quality.

Results

Among 51 subjects (66% male, average age: 63 ± 15.8), the prevalence of positive CT findings was moderate (overall: 11.7%). Overall, image quality of the pulmonary, aortic and coronary vasculature was good (1.26 ± 0.43 and CNR: 2.52) with an average radiation dose of 3.82 mSv and 3.2% of segments rated non-evaluable. The image quality was lowest in the coronary arteries (p = 0.02), depending on the heart rate (r = 0.52, p < 0.001). In subjects with a heart rate of ≤65 bpm (n = 30) subjective image quality and CNR of the coronary arteries were higher (1.6 ± 0.5 vs. 2.1 ± 0.5, p = 0.03 and 1.21 ± 0.3 vs. 1.02 ± 0.3, p = 0.05) with only 1.5% segments classified as non-evaluable.

Conclusion

High-pitch dual-spiral comprehensive cardiothoracic CT provides low radiation exposure with excellent image quality at heart rates ≤65 bpm. In subjects with higher heart rates, image quality of the aortic and pulmonary vasculature remains excellent, while the assessment of the coronary arteries degrades substantially.     

Clinical usefulness of the visibility of the transcerebral veins at 3T on T2*-weighted sequence in acute stroke patients

Objectives

The objective of this work was to investigate the clinical usefulness of the visibility of the transcerebral veins (VTV) in acute ischemic stroke patients at 3 T.

Methods

Sixty consecutive carotid artery territory stroke patients were included retrospectively. Two readers categorized the VTV on T2*-weighted sequence at 3 T for each hemisphere, and asymmetry of this sign was assessed between each hemisphere by an asymmetry index (AI) using a three-item scale. The VTV and AI were correlated with clinical and radiological covariates. Particular interest was focused on patients for whom initial diffusion-weighted imaging alone was inconclusive.

Results

VTV were detected in the stroke hemisphere in 58.3% (n = 35) and in the contralateral side in 10% (n = 6, p < 0.0001). Asymmetry of the VTV between ischemic and contralateral hemispheres was present in 53.3% (n = 32). Intracranial artery occlusion, final infarct volume and symptomatic hemorrhagic transformation were correlated with a higher AI at baseline (ρ = 0.563, ρ = 0.291, and ρ = 0.285, p < 0.05, respectively). Three hyperacute stroke patients with subtle DWI high signal intensity at admission demonstrated VTV.

Conclusions

The pathological value of the VTV seems to reside in its asymmetry between hemispheres, as it was correlated with important clinical parameters. This study also suggests that the VTV could be a supportive finding in stroke diagnosis, especially when DWI is unreliable.     

Dynamic 3D-MR-angiography for assessing rheumatoid disease of the hand--a feasibility study

Purpose

To investigate highly temporally resolved MR-angiography (MRA) with time-resolved imaging with stochastic trajectories (TWIST) of the hand as supplementary tool for dynamic assessment of synovitis and vascular pathologies in rheumatoid diseases.

Material and methods

A coronal dynamic TWIST–MRA-sequence (0.7 mm × 0.7 mm × 1.4 mm, temporal resolution 2.5 s, time of acquisition 4 min) of the predominantly affected hand of 17 patients with suspected rheumatoid disease was acquired after contrast administration (Multihance, Bracco Imaging SpA) at 3 T (Magnetom VERIO, 8-channel-knee-coil, Siemens Healthcare). As standard of reference, contrast enhanced non fat-saturated coronal and fat-saturated axial T1-w sequences were acquired. These static sequences and the dynamic TWIST–MRA–maximum-intensity-projections (MIP) were separately assessed by two readers in consensus, recording the number of synovial lesions (wrist, intercarpal, metacarpophaleangal/proximal/distal interphalangeal joints), signs of tenosynovitis and vasculitis. Diagnostic confidence was rated (4-point-scale: 4 = excellent; 1 = non-diagnostic). Statistical significance was tested using the Wilcoxon-rank-sum-test.

Results

An insignificantly lower number of synovial lesions (n = 72 vs. 89; p = 0.1) and only 3/9 cases with tenosynovitis were identified by the TWIST–MRA. For detected lesions, diagnostic confidence was comparable (MRA: 3.64; static T1-w post contrast: 3.47). In patients with high clinical activity dynamic MRA showed very early synovial enhancement. Only dynamic MRA detected 3 cases of vasculitis (subsequently confirmed with digital-subtraction-angiography).

Conclusion

TWIST–MRA facilitates fast detection of synovitis. Although dynamic MRA of the hand is inferior to static contrast enhanced sequences in assessing the number of synovitic and tenosynovitic lesions, its high temporal resolution allows for fast visual grading of disease activity and assessment of vasculitis without additional contrast material application.     

Comparison of arterial and venous coronary artery bypass flow measurements using 3-T magnetic resonance phase contrast imaging

Objective

Comparison of arterial and venous coronary artery bypass flow measurements using 3-T magnetic resonance (MR) phase contrast in correlation with intraoperative Doppler flow measurements.

Methods

Fifty-six coronary bypasses (right coronary artery n = 18, left internal mammary artery to left anterior descending artery n = 16, marginal artery n = 7, circumflex artery n = 7, diagonal artery n = 6, left anterior descending artery n = 1, and right internal mammary artery to right coronary artery n = 1) were studied in 27 asymptomatic patients. In this prospective study, each bypass was studied intra-operatively using Doppler flow measurement. Within one week post surgery, patients were studied using a 3-T MR scanner (Magnetom Verio, Siemens, Erlangen, Germany) using velocity encoded phase-contrast flow measurements.

Results

Intraoperative Doppler flow measurements demonstrated regular flow patterns in all vascular territories supplied. All bypasses were patent on MRI and flow measurement results were as follows: median flow 60 ml/min (interquartile range (IQR): 37.5–78.5 ml/min). For comparison, the corresponding median intraoperative flow was 58 ml/min (IQR: 41–80 ml/min) (p < 0.001; R = 0.44). Linear regression analysis demonstrated a significant correlation for venous bypasses (p = 0.0002; R = 0.48), but not for arterial bypasses (p = 0.09; R = 0.24).

Conclusion

This study demonstrated that MR flow measurements of venous bypass grafts agreed more with Doppler than arterial bypass grafts. However, bypass patency was confirmed for all patients. In the future, this technique may be used for non invasive coronary bypass graft follow-up.     

Stenosis Asymmetry Index (SAI) between symptomatic and asymptomatic patients in the analysis of carotid arteries. A study using CT angiography

Purpose

Extracranial carotid artery stenosis is accepted as a significant risk factor for cerebrovascular events. The purpose of this paper was to evaluate whether the Stenosis Asymmetry Index (SAI) between carotid arteries (in symptomatic and asymptomatic patients) can be considered a further parameter in the stroke risk stratification.

Materials and methods

60 consecutive symptomatic (males 36; median age 64) patients and 60 non symptomatic patients matched for gender and age, were analyzed using a 40-detector-row CT angiography. Each patient was analyzed by injecting 80 mL of contrast material at a 5 mL\s flow rate. Stenosis degree of 240 carotids was calculated according to NASCET method. For each patient, the ratio between the most severe stenosis and the contralateral was calculated to obtain the SAI. Multiple logistic regression analysis was performed and ROC curve was also calculated.

Results

Results of our study indicate a mean SAI of 1.48 (±0.35 SD) in the asymptomatic group and a mean SAI of 1.69 (±0.53 SD) in the symptomatic group with a statistically significant difference (p value = 0.0204). The multiple logistic regression analysis did not find statistically significant association between SAI and symptoms. The ROC curve analysis indicated that an SAI value of 1.8 has a specificity of 84.31% presence of cerebral symptoms whereas using a 1.2 SAI we obtained a sensitivity of 88.24%.

Conclusion

Results of our study suggest that a SAI > 1.8 has a good sensitivity in identifying the association with cerebrovascular events.     

CT angiography of various superficial femoral artery stents: an in vitro phantom study

Purpose

To evaluate CT reconstruction parameters to improve stent lumen visualization in vitro.

Material and methods

12 latest superficial femoral artery (SFA) stents were placed in a vessel phantom (diameter 4.7 mm, intravascular attenuation 250 HU, extravascular density 50 HU). Stents were imaged with a 128-slice scanner (SOMATOM Definition Flash, Siemens, Germany) with standard parameters: 120 kV, 200 mAs, collimation 128 mm × 0.6 mm. Different reconstruction parameters were evaluated: B26f, B30f, B45f, B46f and B60f kernel; slice thickness of 0.6, 2.0 and 5.0 mm. To measure visualization characteristics, stent lumen diameter and intraluminal attenuation were assessed.

Results

Best stent lumen visualization could be obtained using the B46f kernel (p < 0.001). The visible stent lumen ranged from 66.4% to 83.3% with a mean diameter of 77.7 ± 4.6%. Nitinol stents showed a significant improved lumen visibility compared to the cobalt–chromium stent (p = 0.02). The most realistic lumen attenuation was achieved using the B46f kernel with a mean attenuation of 259.3 ± 8.9 HU. The visible lumen diameter in protocols with 5 mm slice thickness was significantly lower (70.0 ± 4.9%) compared to thinner slices (p < 0.001).

Conclusion

CTA of SFA stents should be reconstructed with a slice thickness of 2.0 mm and a B46f kernel to achieve best image quality and to become more sensitive to exclude instent restenosis.     

Association of carotid atherosclerotic plaque features with acute ischemic stroke: A magnetic resonance imaging study

Background and purpose

It remains unclear whether direct vessel wall imaging can identify carotid high-risk lesions in symptomatic subjects and whether carotid plaque characteristics are more effective indicators for cerebral infarct severity than stenosis. This study sought to determine the associations of carotid plaque characteristics by MR imaging with stenosis and acute cerebral infarct (ACI) sizes on diffusion weighted imaging (DWI).

Materials and methods

One hundred and fourteen symptomatic patients underwent carotid and brain MRI. ACI volume was determined from symptomatic internal carotid artery territory on DWI images. Ipsilateral carotid plaque morphological and compositional characteristics, and stenosis were also determined. The relationships between carotid plaque characteristics, stenosis and ACIs size were then evaluated.

Results

In carotid arteries with 30–49% stenosis, 86.7% and 26.7% were found to have lipid-rich necrotic core (LRNC) and intraplaque hemorrhage, respectively. Furthermore, 45.8% of carotid arteries with 0–29% stenosis developed LRNCs. Carotid morphological measurements, such as % wall volume, and the LRNC size were significantly associated with ipsilateral ACIs volume before and after adjustment for significant demographic factors (age and LDL) or stenosis in patients with carotid plaque (all p < 0.05).

Conclusions

A substantial number of high-risk plaques characterized by vessel wall imaging exist in carotid arteries with lower grade stenosis. In addition, carotid plaque characteristics, particularly the % wall volume and LRNC size, are independently associated with cerebral infarction as measured by DWI lesions. Our findings indicate that characterizing atherosclerotic plaque by MR vessel wall imaging might be useful for stratification of plaque risk and infarction severity.     

Utility of USPIO-enhanced MR imaging to identify inflammation and the fibrous cap: a comparison of symptomatic and asymptomatic individuals

Background and purpose

Inflammation is a risk factor the vulnerable atheromatous plaque. This can be detected in vivo on high-resolution magnetic resonance (MR) imaging using a contrast agent, Sinerem™, an ultra-small super-paramagnetic iron oxide (USPIO). The aim of this study was to explore whether there is a difference in the degree of MR defined inflammation using USPIO particles, between symptomatic and asymptomatic carotid plaques. We report further on its T₁ effect of enhancing the fibrous cap, which may allow dual contrast resolution of carotid atheroma.

Methods

Twenty patients with carotid stenosis (10 symptomatic and 10 asymptomatic) underwent multi-sequence MR imaging before and 36 h post-USPIO infusion. Images were manually segmented into quadrants and signal change in each quadrant was calculated following USPIO administration. Mean signal change across all quadrants were compared between the two groups.

Results

Symptomatic patients had significantly more quadrants with a signal drop than asymptomatic individuals (75% vs. 32%, p < 0.01). Asymptomatic plaques had more quadrants with signal enhancement than symptomatic ones (68% vs. 25%, p < 0.05); their mean signal change was also higher (46% vs. 15%, p < 0.01) and this appeared to correlate with a thicker fibrous cap on histology.

Conclusions

Symptomatic patients had more quadrants with signal drop suggesting larger inflammatory infiltrates. Asymptomatic individuals showed significantly more enhancement possibly suggesting greater stability as a result of thicker fibrous caps. However, some asymptomatic plaques also had focal areas of signal drop, suggesting an occult macrophage burden. If validated by larger studies, USPIO may be a useful dual contrast agent able to improve risk stratification of patients with carotid stenosis and inform selection for intervention.     

Nonenhanced ECG-gated time-resolved 4D steady-state free precession (SSFP) MR angiography (MRA) of cerebral arteries: comparison at 1.5T and 3T

Purpose

To compare image quality of nonenhanced time-resolved 4D steady-state free precession MR angiography (4D SSFP MRA) of cerebral arteries at 1.5 T and 3 T.

Materials and methods

12 healthy subjects (mean age 29.4 ± 6.9 years) were studied at both 1.5 T and 3 T. Two different positions of the acquisition slab were evaluated; in one acquisition the imaging slab included the carotid siphon (“S_low”), in the other acquisition the imaging slab was placed superior to the carotid siphon (“S_high”). Subjective image quality of cerebral arteries was assessed independently by two readers on a 4-point scale. Relative Signal-to-Noise-Ratio (SNR) was determined for the M1 segment of the middle cerebral artery.

Results

Subjective image quality of the anterior cerebral artery (segments A1, A2) was significantly higher at 1.5 T as compared to 3 T, while 3 T provided significantly higher image quality for segment P3 of the posterior cerebral artery. For the middle cerebral artery (segments M1–M3), image quality was significantly higher at 1.5 T than at 3 T when the carotid siphon was included in the acquisition slab (“S_low”), while no significant difference was found between 1.5 T and 3 T with “S_high”. Relative SNR was significantly higher at 1.5 T (23.1 ± 5.1) as compared to 3 T (12.1 ± 7.8) for “S_low” and significantly higher at 3 T (29.8 ± 5.9) than at 1.5 T (24.2 ± 3.6) for “S_high”.

Conclusion

Our results indicate that 4D SSFP MRA should preferably be performed at 1.5 T with inclusion of the carotid siphon in the acquisition slab, which might be required for the assessment of intracranial collateral flow.     

Characterisation of focal liver lesions with unenhanced and contrast enhanced low MI real time ultrasound: on-site unblinded versus off-site blinded reading

Objective

To compare on-site and blinded off-site reading of baseline ultrasound (US) and contrast enhanced ultrasound (CEUS) for classification and characterisation of focal liver lesions.

Materials and methods

99 patients (57 women and 42 men, age range 18–89 years, mean age: 59 years) with 53 malignant and 46 benign liver lesions were studied with unenhanced US followed by contrast enhanced US after injection of 2.4 ml SonoVue^® (Bracco, Milano, Italy). Image interpretation was performed on-site with clinical information available by consensus of two readers and off-site by two independent blinded readers at two different centers. Comparison of pre and post contrast scans and of the different readers was performed. Reference examinations were histology, intraoperative US, MRI or CT.

Results

Sensitivity for malignancy improved from 81/89/66% (on-site/off-site reader 1/2) before to 100/96/96% post contrast administration (p < 0.05, except for reader 1). Specificity improved from 48/48/54% on baseline US to 89/80/76% on CEUS (p < 0.05). Accuracy for specific lesion diagnosis was 62/59/50% pre and 90/77/72% post contrast (p < 0.05). Classification and characterisation post contrast were mildly inferior for off-site reading. Agreement between on-site and off-site readers of unenhanced scans was fair (κ = 0.29–0.39) while it was good for CEUS (κ = 0.63–0.79).

Conclusions

CEUS improves classification and characterisation of focal liver lesions and interobserver agreement compared to conventional US. Classification and characterisation post contrast were mildly but statistically significantly better for on-site than for off-site reading.     

Prediction of the presence of renal artery stenosis by calcium scoring of the abdominal aorta

Objective

To establish a method for estimating the probability of renal artery stenosis (RAS) based on the calcium volume score of the aorta (ACS).

Materials and Methods

In a retrospective observation study, CT angiographies acquired on a 64-slice MDCT scanner were analyzed for 1351 patients (female: 531; male 826; mean age 60.9 ± 17.7 years). A volumetric scoring method was used, detecting plaques with a density of more than 600 HU.

Results

13.8% of the patients showed a stenosis >50%, 4.1% a stenosis >70%. The ACS was 0.61 ± 1.01 ml calcium. The sensitivity for detection of RAS >50% and RAS >80% was 0.9572 and 1.0, respectively. The negative predictive value (NPV) of a lack of calcification for excluding RAS >50% and RAS >80% was 0.9752 and 1, respectively. As ACS increased, the specificity for RAS >50% increased to 0.9390. With an ACS of 0.380 ml, accuracy reached a maximum of 0.6585. ROC analyses yielded an area under the curve of 0.88 (p < 0.0001). Sensitivity, specificity, NPV and PPV are indicated in relation to the degree of RAS, as well as the diagnostic yield of the method, which is valuable in patients older than 50 years.

Conclusion

Due to its extremely high sensitivity and NPV, the ACS is a very useful screening method for RAS. The validity of the method, as well as its diagnostic value is equivalent to that of coronary artery calcium scoring. Lack of calcifications of the aorta renders atherosclerotic RAS highly improbable.