Imaging Carotid Atherosclerosis Plaque Ulceration: Comparison of Advanced Imaging Modalities and Recent Developments.

Atherosclerosis remains the leading cause of long-term mortality and morbidity worldwide, despite remarkable advancement in its management. Vulnerable atherosclerotic plaques are principally responsible for thromboembolic events in various arterial territories such as carotid, coronary, and lower limb vessels. Carotid plaque ulceration is one of the key features associated with plaque vulnerability and is considered a notable indicator of previous plaque rupture and possible future cerebrovascular events. Multiple imaging modalities have been used to assess the degree of carotid plaque ulceration for diagnostic and research purposes. Early diagnosis and management of carotid artery disease could prevent further cerebrovascular events. In this review, we highlight the merits and limitations of various imaging techniques for identifying plaque ulceration.

Combined MR direct thrombus imaging and non-contrast magnetic resonance venography reveal the evolution of deep vein thrombosis: a feasibility study.

OBJECTIVES: Lower limb deep venous thrombosis (DVT) is a common condition with high morbidity and mortality. The aim of the study was to investigate the temporal evolution of the acute thrombus by magnetic resonance imaging (MRI) and its relationship to venous recanalization in patients with recurrent DVTs. METHODS: Thirteen patients with newly diagnosed lower limb DVTs underwent MRI with non-contrast MR venography (NC-MRV) and MR direct thrombus imaging (MR-DTI), an inversion-recovery water-selective fast gradient-echo acquisition. Imaging was performed within 7 days of the acute thrombotic event, then at 3 and 6 months. RESULTS: By 3 months from the thrombotic event a third of the thrombi had resolved and by 6 months about half of the cases had resolved on the basis of vein recanalisation using NC-MRV. On the initial MR-DTI acute thrombus was clearly depicted by hyperintense signal, while the remaining thrombi were predominantly low signal at 3 and 6 months. Some residual thrombi contained small and fragmented persisting hyperintense areas at 3 months, clearing almost completely by 6 months. CONCLUSIONS: Our study suggests that synergistic venous assessment with combined NC-MRV and MR-DTI is able to distinguish acute venous thrombosis from the established (old) or evolving DVT detected by ultrasound. KEY POINTS: • MRI can distinguish between acute and evolving or chronic lower limb DVT • Two advanced MRI techniques can follow the evolution of lower limb DVT • MRI could be used to avoid an incorrect diagnosis of recurrent DVT • MRI could help avoid the risks and complications of lifelong anticoagulation therapy.

Superficial fibular nerve variations of fascial piercing: A meta-analysis and clinical consideration.

The superficial fibular (peroneal) nerve (SFN) is one of the successive branches of the common fibular (peroneal) nerve and goes on to bifurcate into the medial dorsal cutaneous (MDN) and intermediate dorsal cutaneous (IDN) nerves. The SFN is a main contributor to sensory innervation of the foot and lower leg. It varies widely in its penetrance of the deep (crural) fascia, and differences in its subsequent course can result in iatrogenic injuries. Articles on the prevalence of this anatomical variation were identified by a comprehensive database search. The data collected were extracted and pooled into a meta-analysis. A total of 14 articles (n = 665 lower limbs) were included on the meta-analysis of SFN variations in fascial piercing. The normal Type 1 variation, where the SFN pierces the deep fascia as a single entity and later bifurcates into the MDN and IDN, had a pooled prevalence of 82.7% (95%CI: 74.0-89.4). The Type 2 variant, where the SFN bifurcates early and then pierces the fascial layer separately as the MDN and IDN, had a pooled prevalence of 15.6% (95%CI: 8.9-23.6). Type 3, when the SFN penetrates the deep fascia and courses similar to the MDN with absent IDN was noted in 1.8% (95%CI: 0.0-4.9) of cases. A substantial portion of the population has a pattern of SFN piercing that deviates from the normal Type 1 anatomy. It is recommended that possible SFN variants in patients should be addressed thoroughly to help prevent iatrogenic injuries and postoperative complications. Clin. Anat. 30:120-125, 2017. © 2016 Wiley Periodicals, Inc.

Uterine artery pulsatility and resistivity indices in pregnancy: Comparison of MRI and Doppler US.

OBJECTIVE: The aim of this work was to evaluate whether the uterine arteries (UtA) could be identified and their flow profiles measured during a fetal MRI examination. A comparison was performed against same day sonographic Doppler assessment. METHODS: 35 normal, healthy, singleton pregnancies at 28-32 weeks gestation underwent routine Doppler examination, followed by MRI examination. The resistivity index (RI) and pulsatility index (PI) of the left and right UtA were measured using phase contrast MRI. Bland Altman statistics were used to compare MRI and ultrasound results. RESULTS: Sixty-nine comparable vessels were analysed. Six vessels were excluded due to artefact or technical error. Bland-Altman analysis demonstrated the ultrasound indices were comparable, although systematically lower than the MRI indices; Right UtA RI bias -0.03 (95% limits of agreement (LOA) -0.27 to +0.20), and left UtA RI bias -0.06 (95% LOA -0.26 to +0.14); Right UtA PI bias -0.06 (95% LOA -0.50 to +0.38), Left UtA PI bias -0.11 (95% LOA -0.54 to +0.32). The inter-rater agreement for the MRI derived PI and RI analysis was good. CONCLUSION: This study demonstrates that in the majority of early third trimester pregnancies, the uterine arteries can be identified, and their flow profiles measured using MRI, and that the derived PI and RI values are comparable with Doppler ultrasound values.

Amniotic fluid volume: Rapid MR-based assessment at 28-32 weeks gestation.

OBJECTIVES: This work evaluates rapid magnetic resonance projection hydrography (PH) based amniotic fluid volume (AFV) estimates against established routine ultrasound single deepest vertical pocket (SDVP) and amniotic fluid index (AFI) measurements, in utero at 28-32 weeks gestation. Manual multi-section planimetry (MSP) based measurement of AFV is used as a proxy reference standard. METHODS: Thirty-five women with a healthy singleton pregnancy (20-41 years) attending routine antenatal ultrasound were recruited. SDVP and AFI were measured using ultrasound, with same day MRI assessing AFV with PH and MSP. The relationships between the respective techniques were assessed using linear regression analysis and Bland-Altman method comparison statistics. RESULTS: When comparing estimated AFV, a highly significant relationship was observed between PH and the reference standard MSP (R(2) = 0.802, p < 0.001). For the US measurements, SDVP measurement related most closely to amniotic fluid volume, (R(2) = 0.470, p < 0.001), with AFI demonstrating a weaker relationship (R(2) = 0.208, p = 0.007). CONCLUSION: This study shows that rapid MRI based PH measurement is a better predictor of AFV, relating more closely to our proxy standard than established US techniques. Although larger validation studies across a range of gestational ages are required this approach could form part of MR fetal assessment, particularly where poly- or oligohydramnios is suspected. KEY POINTS: • MR projection hydrography can be used to estimate amniotic fluid volume. • MR projection hydrography relies on the T2w signal from amniotic fluid. • Amniotic fluid volume (AFV) is more accurately assessed than with ultrasound.

Advances in MRI for the evaluation of carotid atherosclerosis.

Carotid artery atherosclerosis is an important source of mortality and morbidity in the Western world with significant socioeconomic implications. The quest for the early identification of the vulnerable carotid plaque is already in its third decade and traditional measures, such as the sonographic degree of stenosis, are not selective enough to distinguish those who would really benefit from a carotid endarterectomy. MRI of the carotid plaque enables the visualization of plaque composition and specific plaque components that have been linked to a higher risk of subsequent embolic events. Blood suppressed T1 and T2 weighted and proton density-weighted fast spin echo, gradient echo and time-of-flight sequences are typically used to quantify plaque components such as lipid-rich necrotic core, intraplaque haemorrhage, calcification and surface defects including erosion, disruption and ulceration. The purpose of this article is to review the most important recent advances in MRI technology to enable better diagnostic carotid imaging.

3T diffusion-weighted MRI of the thyroid gland with reduced distortion: preliminary results.

OBJECTIVE: Single-shot diffusion-weighted (DW) echo planar imaging (EPI), which is commonly used for imaging the thyroid, is characterised by severe blurring and distortion. The objectives of this work were: 1, to show that a reduced-field of view (r-FOV) DW EPI technique can improve image quality; and 2, to investigate the effect of different reconstruction strategies on the resulting apparent diffusion coefficients (ADCs). METHODS: We implemented a single-shot, r-FOV DW EPI technique with a two-dimensional radiofrequency excitation pulse for DW imaging of the thyroid at 3T. Images were reconstructed using root sum of squares (SOS) and an optimal-B1 reconstruction (OBR). Phantom and in vivo experiments were performed to compare r-FOV and conventional full-FOV DW EPI with root SOS and OBR. RESULTS: r-FOV with OBR substantially improved image quality at 3T. In phantoms, r-FOV gave more accurate ADCs than full-FOV. In vivo r-FOV always gave lower ADC values with respect to the full-FOV technique irrespective of the reconstruction used and whether only two or multiple b-values were used to compute the ADCs. CONCLUSION: r-FOV DW EPI can reduce image blurring and distortion at the expense of a low signal-to-noise ratio. OBR is a promising reconstruction technique for accurate ADC measurements in lower signal-to-noise ratio regimes, although further studies are needed to characterise its performance. ADVANCES IN KNOWLEDGE: DW imaging of the thyroid at 3T could potentially benefit from r-FOV acquisition strategies, such as the r-FOV DW EPI technique proposed in this paper.

Imaging vascular function for early stage clinical trials using dynamic contrast-enhanced magnetic resonance imaging.

Many therapeutic approaches to cancer affect the tumour vasculature, either indirectly or as a direct target. Dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) has become an important means of investigating this action, both pre-clinically and in early stage clinical trials. For such trials, it is essential that the measurement process (i.e. image acquisition and analysis) can be performed effectively and with consistency among contributing centres. As the technique continues to develop in order to provide potential improvements in sensitivity and physiological relevance, there is considerable scope for between-centre variation in techniques. A workshop was convened by the Imaging Committee of the Experimental Cancer Medicine Centres (ECMC) to review the current status of DCE-MRI and to provide recommendations on how the technique can best be used for early stage trials. This review and the consequent recommendations are summarised here. Key Points • Tumour vascular function is key to tumour development and treatment • Dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) can assess tumour vascular function • Thus DCE-MRI with pharmacokinetic models can assess novel treatments • Many recent developments are advancing the accuracy of and information from DCE-MRI • Establishing common methodology across multiple centres is challenging and requires accepted guidelines.

Signal-to-noise ratio increase in carotid atheroma MRI: a comparison of 1.5 and 3 T.

OBJECTIVES: This study reports quantitative comparisons of signal-to-noise ratio (SNR) at 1.5 and 3 T from images of carotid atheroma obtained using a multicontrast, cardiac-gated, blood-suppressed fast spin echo protocol. METHODS: 18 subjects, with carotid atherosclerosis (>30% stenosis) confirmed on ultrasound, were imaged on both 1.5 and 3 T systems using phased-array coils with matched hardware specifications. T(1) weighted (T(1)W), T(2) weighted (T(2)W) and proton density-weighted (PDW) images were acquired with identical scan times. Multiple slices were prescribed to encompass both the carotid bifurcation and the plaque. Image quality was quantified using the SNR and contrast-to-noise ratio (CNR). A phantom experiment was also performed to validate the SNR method and confirm the size of the improvement in SNR. Comparisons of the SNR values from the vessel wall with muscle and plaque/lumen CNR measurements were performed at a patient level. To account for the multiple comparisons a Bonferroni correction was applied. RESULTS: One subject was excluded from the protocol owing to image quality and protocol failure. The mean improvement in SNR in plaque was 1.9, 2.1 and 2.1 in T(1)W, T(2)W and PDW images, respectively. All plaque SNR improvements were statistically significant at the p<0.05 level. The phantom experiment reported an improvement in SNR of 2.4 for PDW images. CONCLUSIONS: Significant gains in SNR can be obtained for carotid atheroma imaging at 3 T compared with 1.5 T. There was also a trend towards increased CNR. However, this was not significant after the application of the Bonferroni correction.

Magnetic resonance elastography: feasibility of liver stiffness measurements in healthy volunteers at 3T.

AIM: To demonstrate the feasibility of obtaining liver stiffness measurements with magnetic resonance elastography (MRE) at 3T in normal healthy volunteers using the same technique that has been successfully applied at 1.5 T. METHODS AND MATERIALS: The study was approved by the local ethics committee and written informed consent was obtained from all volunteers. Eleven volunteers (mean age 35 ± 9 years) with no history of gastrointestinal, hepatobiliary, or cardiovascular disease were recruited. The magnetic resonance imaging (MRI) protocol included a gradient echo-based MRE sequence using a 60 Hz pneumatic excitation. The MRE images were processed using a local frequency estimation inversion algorithm to provide quantitative stiffness maps. Adequate image quality was assessed subjectively by demonstrating the presence of visible propagating waves within the liver parenchyma underlying the driver location. Liver stiffness values were obtained using manually placed regions of interest (ROI) outlining the liver margins on the gradient echo wave images, which were then mapped onto the corresponding stiffness image. The mean stiffness values from two adjacent sections were recorded. RESULTS: Eleven volunteers underwent MRE. The quality of the MRE images was adequate in all the volunteers. The mean liver stiffness for the group was 2.3 ± 0.38 kPa (ranging from 1.7-2.8 kPa). CONCLUSIONS: This preliminary work using MRE at 3T in healthy volunteers demonstrates the feasibility of liver stiffness evaluation at 3T without modification of the approach used at 1.5 T. Adequate image quality and normal MRE values were obtained in all volunteers. The obtained stiffness values were in the range of those reported for healthy volunteers in previous studies at 1.5 T. There was good interobserver reproducibility in the stiffness measurements.

DCE and DW MRI in monitoring response to androgen deprivation therapy in patients with prostate cancer: a feasibility study.

Androgen deprivation therapy (ADT) is a key primary treatment for advanced and metastatic prostate cancer and is an important neoadjuvant before radiotherapy. We evaluated 3.0 T dynamic contrast-enhanced MRI and diffusion-weighted (DW) MRI in monitoring ADT response. Twenty-three consecutive patients with prostate cancer treated by primary ADT were included. Imaging was performed at baseline and 3 months posttreatment with ADT. After 3 months therapy there was a significant reduction in all dynamic contrast-enhanced MRI parameters measured in tumor regions of interest (K(trans), k(ep), v(p), IAUGC-90); P < 0.001. Areas of normal-appearing peripheral zone showed no significant change; P = 0.285-0.879. Post-ADT, there was no significant change in apparent diffusion coefficient values in tumors, whilst apparent diffusion coefficient values significantly decreased in areas of normal-appearing peripheral zone, from 1.786 × 10(-3) mm(2) /s to 1.561 × 10(-3) mm(2) /s; P = 0.007. As expected the median Prostate-Specific Antigen (PSA) significantly reduced from 30 ng/mL to 1.5 ng/mL posttreatment, and median prostate volume dropped from 47.6 cm(3) to 24.9 cm(3) ; P < 0.001. These results suggest that dynamic contrast-enhanced MRI and diffusion-weighted MRI offer different information but that both could prove useful adjuncts to the anatomical information provided by T2-weighted imaging. dynamic contrast-enhanced as a marker of angiogenesis may help demonstrate ADT resistance and diffusion-weighted imaging may be more accurate in determining presence of tumor cell death versus residual tumor.

In vivo MRI-based 3D mechanical stress-strain profiles of carotid plaques with juxtaluminal plaque haemorrhage: an exploratory study for the mechanism of subsequent cerebrovascular events.

OBJECTIVES: Atherosclerotic plaque features, such as fibrous cap erosion, ulceration and rupture and presence of haemorrhage in carotid plaque are two important characteristics associated with subsequent cerebrovascular events and juxtaluminal haemorrhage/thrombus (JLH/T) indicates these two high-risk characteristics. This study aims to investigate the association between JLH/T and subsequent events in patients suffering from transient ischaemic attack (TIA). Three-dimensional mechanical analysis was employed to represent the critical mechanical stress (P-CStress) and stretch (P-CStretch) within the plaque. METHODS: Fifty TIA patients with mild-to-moderate carotid stenosis (30-69%) underwent high-resolution magnetic resonance imaging (MRI) within 72 h of the acute event and eight were excluded from the analysis due to various reasons. A total of 21 patients were found to have JLH/T in the carotid plaque and 21 did not (N-JLH/T). During a 2-year follow-up period, 11 (52.4%) patients in the JLH/T group experienced recurrent events and none in the N-JLH/T group. Three-dimensional plaque structure was reconstructed based on the in vivo MRI for the mechanical analysis. RESULTS: P-CStress of both groups was comparable (N-JLH/T: 174.45 ± 63.96 kPa vs. JLH/T: 212.60 ± 89.54 kPa; p = 0.120), but P-CStretch of JLH/T was significantly bigger than that of N-JLH/T (N-JLH/T: 1.21 ± 0.08 vs. JLH/T: 2.10 ± 0.53; p < 0.0001). Moreover, there were much bigger variations in stress and stretch of the JLH/T group during one cardiac cycle than in those of N-JLH/T group. CONCLUSIONS: In vivo MRI-depicted JLH/T might be a high risk factor initiating recurrent events, as big deformation appearing around the rupture site might prevent healing and tear the haemorrhage/thrombus away from the host structure and prompt further thrombo-embolic events.

High-resolution magnetic resonance imaging-based biomechanical stress analysis of carotid atheroma: a comparison of single transient ischaemic attack, recurrent transient ischaemic attacks, non-disabling stroke and asymptomatic patient groups.

BACKGROUND: Vulnerable carotid plaques are associated with cerebrovascular ischaemic events. High-resolution magnetic resonance (MR) imaging not only allows the morphological assessment of such plaques, but also provides geometrical data, which can be used for biomechanical stress analysis. We assess its utility to assess the plaque stress profiles of symptomatic (transient ischaemic attack (TIA) and non-disabling stroke) and asymptomatic patients. METHODS: A total of 70 consecutive patients with confirmed underlying carotid artery disease underwent carotid MR imaging of their carotid artery in a 1.5-T MR system using a standard carotid atheroma imaging protocol. MR images were manually segmented for different plaque components and used for biomechanical stress analysis. The maximum critical stress (M-CStress) for various clinical groups was determined and compared. RESULTS: M-CStress of symptomatic plaques (n = 45) was significantly higher than for asymptomatic plaques (n = 25) (median (interquartile range (IQR): 275 kPa (190-390) vs. 165 kPa (120-200), p = 0.0001)). Within the symptomatic group, no M-CStress differences were present between the TIA (n = 30) and stroke (n = 15) patients (260 kPa (190-370) vs. 295 kPa (200-510), p = 0.31). Within the TIA patient cohort, those who had presented with recurrent TIAs (n = 6) had significantly higher stresses than patients who had suffered a single episode (n = 24) (425 kPa (285-580) vs. 250 kPa (180-310), p = 0.001). CONCLUSIONS: Symptomatic carotid plaques, particularly those associated with recurrent TIAs, have high biomechanical stresses. As there is pre-existing evidence to suggest that high biomechanical stresses are associated with plaque vulnerability, MR-imaging-based stress analysis has the potential to identify high-risk patients with vulnerable plaques.

Ultrasmall superparamagnetic iron oxide-enhanced magnetic resonance imaging of abdominal aortic aneurysms--a feasibility study.

OBJECTIVES: Abdominal aortic aneurysms (AAAs), being predominantly atherosclerotic in nature, have underlying inflammatory activity. As it is well established that ultrasmall superparamagnetic iron oxide (USPIO) particles accumulate in the macrophages within atheromatous lesions, USPIO-enhanced magnetic resonance (MR) imaging can be potentially effective in the quantification of the associated inflammatory processes. METHODS: A total of 14 patients underwent USPIO-enhanced MR imaging using a 1.5T-MR system. Quantitative T(2)* and T(2) relaxation time data were acquired before and 36 h after UPSIO infusion at identical AAA locations. The pre- and post-USPIO-infusion relaxation times (T(2)(∗) and T(2)) were quantified and the correlation between pre- and post-USPIO infusion T(2)* and T(2) values was investigated. RESULTS: There was a significant difference between pre- and post-infusion T(2)* and T(2) values (both respective p-values = 0.005). A significant correlation between T(2)* and T(2) values post-USPIO infusion was observed (r = 0.90, p < 0.001), which indicates USPIO uptake by the aortic wall. CONCLUSIONS: Aortic wall inflammation using USPIO-enhanced MR imaging is feasible. Use of quantitative T(2) and T(2)* pulse sequences provides a quantitative method for assessing USPIO uptake by the aortic wall.

Association between biomechanical structural stresses of atherosclerotic carotid plaques and subsequent ischaemic cerebrovascular events--a longitudinal in vivo magnetic resonance imaging-based finite element study.

BACKGROUND: High-resolution magnetic resonance (MR) imaging has been used for MR imaging-based structural stress analysis of atherosclerotic plaques. The biomechanical stress profile of stable plaques has been observed to differ from that of unstable plaques; however, the role that structural stresses play in determining plaque vulnerability remains speculative. METHODS: A total of 61 patients with previous history of symptomatic carotid artery disease underwent carotid plaque MR imaging. Plaque components of the index artery such as fibrous tissue, lipid content and plaque haemorrhage (PH) were delineated and used for finite element analysis-based maximum structural stress (M-C Stress) quantification. These patients were followed up for 2 years. The clinical end point was occurrence of an ischaemic cerebrovascular event. The association of the time to the clinical end point with plaque morphology and M-C Stress was analysed. RESULTS: During a median follow-up duration of 514 days, 20% of patients (n = 12) experienced an ischaemic event in the territory of the index carotid artery. Cox regression analysis indicated that M-C Stress (hazard ratio (HR): 12.98 (95% confidence interval (CI): 1.32-26.67, p = 0.02), fibrous cap (FC) disruption (HR: 7.39 (95% CI: 1.61-33.82), p = 0.009) and PH (HR: 5.85 (95% CI: 1.27-26.77), p = 0.02) are associated with the development of subsequent cerebrovascular events. Plaques associated with future events had higher M-C Stress than those which had remained asymptomatic (median (interquartile range, IQR): 330 kPa (229-494) vs. 254 kPa (166-290), p = 0.04). CONCLUSIONS: High biomechanical structural stresses, in addition to FC rupture and PH, are associated with subsequent cerebrovascular events.

Association between white matter ischaemia and carotid plaque morphology as defined by high-resolution in vivo MRI.

OBJECTIVES AND DESIGN: Both carotid plaque morphology and severity of white matter ischaemia (WMI) have been shown to be independent predictors of stroke risk. This study tests the hypothesis that there is an association between carotid plaque morphology as determined by high-resolution carotid MRI and WMI. MATERIALS AND METHODS: Forty patients (80 arteries) with at least 40% stenosis on screening Doppler ultrasound were recruited and underwent high-resolution axial carotid MRI at 1.5 T. In a blinded manner, plaque characteristics such as lipid core, fibrous cap, intraplaque haemorrhage, lumen area, plaque area, and American Heart Association (AHA) classification were qualitatively and quantitatively evaluated. The severity of WMI was independently quantified using a modified Scheltens score based on standard brain Fluid-Attenuated Inversion Recovery. Linear mixed effect models were used to test if carotid plaque characteristics could independently predict severity of WMI. RESULTS: Hypertension (p=0.005) and previous a history of transient ischaemic attack or stroke (p=0.038) were found to be significant predictors of severity of WMI. After accounting for confounding variables, no significant association was found between the modified Scheltens score and lipid core size (p=0.122), fibrous cap status (p=0.991), intraplaque haemorrhage (p=0.708), plaque area (0.835), lumen area (0.371) or an AHA Type VI complex plaque (p=0.195). CONCLUSIONS: Carotid plaque morphology as defined by MRI does not independently predict severity of WMI.

Temporal dependence of in vivo USPIO-enhanced MRI signal changes in human carotid atheromatous plaques.

INTRODUCTION: Ultrasmall superparamagnetic iron oxide (USPIO)-enhanced MRI has been shown to be a useful modality to image activated macrophages in vivo, which are principally responsible for plaque inflammation. This study determined the optimum imaging time-window to detect maximal signal change post-USPIO infusion using T1-weighted (T1w), T2*-weighted (T2*w) and quantitative T2* (qT2*) imaging. METHODS: Six patients with an asymptomatic carotid stenosis underwent high resolution T1w, T2*w and qT2* MR imaging of their carotid arteries at 1.5 T. Imaging was performed before and at 24, 36, 48, 72 and 96 h after USPIO (Sinerem, Guerbet, France) infusion. Each slice showing atherosclerotic plaque was manually segmented into quadrants and signal changes in each quadrant were fitted to an exponential power function to model the optimum time for post-infusion imaging. RESULTS: The power function determining the mean time to convergence for all patients was 46, 41 and 39 h for the T1w, T2*w and qT2* sequences, respectively. When modelling each patient individually, 90% of the maximum signal intensity change was observed at 36 h for three, four and six patients on T1w, T2*w and qT2*, respectively. The rates of signal change decrease after this period but signal change was still evident up to 96 h. CONCLUSION: This study showed that a suitable imaging window for T1w, T2*w and qT2* signal changes post-USPIO infusion was between 36 and 48 h. Logistically, this would be convenient in bringing patients back for one post-contrast MRI, but validation is required in a larger cohort of patients.

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 T(1) 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.

MR-guided direct arthrography of the glenohumeral joint.

AIM: To evaluate the feasibility of magnetic resonance (MR)-guided direct arthrography of the glenohumeral joint with a 1.5 T MR system, performing the entire procedure in a single MR examination. MATERIALS AND METHODS: MR-guided direct arthrography was performed on 11 patients. MR imaging guidance and interactive MR fluoroscopy, with in-room control and display system, were used for needle placement and contrast medium injection. The outcome measures were success or failure of joint puncture, the time taken for introduction of contrast medium, and the diagnostic quality of the subsequent MR arthrography images. RESULTS: Contrast medium was successfully instilled into the joint and diagnostic quality MR arthrography images were obtained in all cases. The median time from initial placement of the skin marker to introduction of the contrast medium was 17 min (range 11-29 min). There were no immediate post-procedure complications. CONCLUSION: Accurate needle placement is feasible in a single MR examination on a commercial 1.5 T closed-bore MR system, using an in-room control and display system together with interactive fluoroscopic imaging, and this was used to provide direct MR arthrography in this study.

Comparison of the inflammatory burden of truly asymptomatic carotid atheroma with atherosclerotic plaques in patients with asymptomatic carotid stenosis undergoing coronary artery bypass grafting: an ultrasmall superparamagnetic iron oxide enhanced magnetic resonance study.

INTRODUCTION: Inflammation is a recognized risk factor for the vulnerable atherosclerotic plaque. The aim of this study was to explore whether there is a difference in the degree of Magnetic Resonance (MR) defined inflammation using Ultra Small Super-Paramagnetic Iron Oxide (USPIO) particles, within carotid atheroma in completely asymptomatic individuals and the asymptomatic carotid stenosis in a cohort of patients undergoing coronary artery bypass grafting (CABG). METHODS: 10 patients awaiting CABG with asymptomatic carotid disease and 10 completely asymptomatic individuals with no documented coronary artery disease underwent multi-sequence MR imaging before and 36 hours post USPIO infusion. Images were manually segmented into quadrants and signal change in each quadrant, normalised to adjacent muscle signal, was calculated following USPIO administration. RESULTS: The mean percentage of quadrants showing signal loss was 94% in the CABG group, compared to 24% in the completely asymptomatic individuals (p<0.001). The carotid plaques from the CABG patients showed a significant mean signal intensity decrease of 16.4% after USPIO infusion (95% CI 10.6% to 22.2%; p<0.001). The truly asymptomatic plaques showed a mean signal intensity increase (i.e. enhancement) after USPIO infusion of 8.4% (95% CI 2.6% to 14.2%; p=0.007). The mean signal difference between the two groups was 24.9% (95% CI 16.7% to 33.0%; p<0.001). CONCLUSIONS: These findings are consistent with the hypothesis that inflammatory atheroma is a systemic disease. The carotid territory is more likely to take up USPIO if another vascular territory is symptomatic.