MRI of cardiac iron overload

Transfusion therapy has greatly improved the survival of transfusion dependent thalassemia major (TM) patients; however, the resultant iron load damages tissues including the heart, liver and endocrine organs. Among these, heart complication still remains the leading cause of mortality. Myocardial iron deposition can occur independently of other solid organ involvement; conversely, the heart may be spared despite heavy siderosis in other tissues. Iron chelation treatment diminishes the risk of hemosiderosis; however, the chelation treatment has its own toxicities and might not be available to all patients due to costs. Close monitoring of individual organ iron concentration and function is thus important for optimization of individual patient care. This review outlines the importance and clinical significance of recently available MRI techniques for monitoring cardiac iron load.

Angiographic features, collaterals, and infarct topography of symptomatic occlusive radiation vasculopathy: a case-referent study

BACKGROUND AND PURPOSE

Occlusive radiation vasculopathy (ORV) predisposes head-and-neck cancer survivors to ischemic strokes.

METHODS

We analyzed the digital subtraction angiography acquired in 96 patients who had first-ever transient ischemic attack or ischemic strokes attributed to ORV. Another age-matched 115 patients who had no radiotherapy but symptomatic high-grade (>70%) carotid stenoses were enrolled as referent subjects. Digital subtraction angiography was performed within 2 months from stroke onset and delineated carotid and vertebrobasilar circulations from aortic arch up to intracranial branches. Two reviewers blinded to group assignment recorded all vascular lesions, collateral status, and infarct pattern.

RESULTS

ORV patients had less atherosclerotic risk factors at presentation. In referent patients, high-grade stenoses were mostly focal at the proximal internal carotid artery. In contrast, high-grade ORV lesions diffusely involved the common carotid artery and internal carotid artery and were more frequently bilateral (54% versus 22%), tandem (23% versus 10%), associated with complete occlusion in one or both carotid arteries (30% versus 9%), vertebral artery (VA) steno-occlusions (28% versus 16%), and external carotid artery stenosis (19% versus 5%) (all P<0.05). With comparable rates of vascular anomaly, ORV patients showed more established collateral circulations through leptomeningeal arteries, anterior communicating artery, posterior communicating artery, suboccipital/costocervical artery, and retrograde flow in ophthalmic artery. In terms of infarct topography, the frequencies of cortical or subcortical watershed infarcts were similar in both groups.

CONCLUSIONS

ORV angiographic features and corresponding collaterals are distinct from atherosclerotic patterns at initial stroke presentation. Clinical decompensation, despite more extensive collateralization, may precipitate stroke in ORV.

Frequency and predictors of proxy-confirmed post-stroke cognitive complaints in lacunar stroke patients without major depression

OBJECTIVE

Many lacunar stroke patients complained of cognitive decline after stroke. This study aims to investigate the factors underlying post-stroke cognitive complaints in these patients.

METHODS

Seventy-five consecutive lacunar stroke patients without major depression were recruited for the study. Stroke severity was measured using NIHSS score and MRI was performed during the acute admission period. At 3 months, objective psychometric performance and depressive symptoms were assessed. Post-stroke cognitive complaints were corroborated by a proxy. Using logistic regression we examined the contribution of demographic features, stroke severity, objective psychometric scores, depressive symptoms, and imaging features (white matter lesion volume and infarct measures) to post-stroke cognitive complaints.

RESULTS

Thirty-two (42.7%) patients had post-stroke cognitive complaints. Patients with post-stroke cognitive complaints had more depressive symptoms and worse psychometric performance than those without. In the multivariate logistic regression model, only the severity of depressive symptoms was independently associated with post-stroke cognitive complaints.

CONCLUSIONS

This study suggests that post-stroke cognitive complaints are frequent among lacunar stroke patients without major depression and are prominently determined by the subclinical depressive symptomatology.

Genetic predisposition of white matter infarction with protein S deficiency and R355C mutation

BACKGROUND

The association between protein S deficiency (PSD) and ischemic stroke is controversial and warrants further investigation.

METHODS

We conducted a genotype and MRI correlation study in a Chinese family in which hereditary PSD cosegregated with premature ischemic strokes. Six out of 11 family members inherited PSD type III in an autosomal dominant manner.

RESULTS

Among all PSD members, a novel missense mutation 1063C→T in exon 10 of protein S alpha (PROS1) was identified, which encoded a substitution of arginine to cysteine at position 355 (R355C) in the first globular domain of laminin A of protein S. Wild-type PROS1 sequences were retained in non-PSD members. MRI detected deep white matter infarctions predominantly distributed in the borderzone regions. The infarct topography was homogeneous in all adult mutant carriers. By contrast, cerebral infarction was absent in nonmutant carriers. Extensive investigation in the family did not reveal any confounding stroke risk. Haplotype analysis with high-density single nucleotide polymorphism markers revealed a 6.1-Mb minimally rearranged region (rs12494685 to rs1598240) in 3q11.2, lod = 3.0. Among the 7 annotated genes in this region, PROS1 is known to be associated with thrombotic disorders. MRI screening in an additional 10 PSD families without R355C showed no cerebral infarction.

CONCLUSIONS

PROS1 R355C mutation cosegregated with PSD type III and premature white matter infarctions in the index family. The findings substantiate an association between PSD and stroke. Study of the mechanism underlying this association may improve our understanding of premature cryptogenic white matter infarction.

International reproducibility of single breathhold T2* MR for cardiac and liver iron assessment among five thalassemia centers

PURPOSE

To examine the reproducibility of the single breathhold T2* technique from different scanners, after installation of standard methodology in five international centers.

MATERIALS AND METHODS

Up to 10 patients from each center were scanned twice locally for local interstudy reproducibility of heart and liver T2*, and then flown to a central MR facility to be rescanned on a reference scanner for intercenter reproducibility. Interobserver reproducibility for all scans was also assessed.

RESULTS

Of the 49 patients scanned, the intercenter reproducibility for T2* was 5.9% for the heart and 5.8% for the liver. Local interstudy reproducibility for T2* was 7.4% for the heart and 4.6% for the liver. Interobserver reproducibility for T2* was 5.4% for the heart and 4.4% for the liver.

CONCLUSION

These data indicate that T2* MR may be developed into a widespread test for tissue siderosis providing that well-defined and approved imaging and analysis techniques are used.

Restrictive right ventricular physiology and right ventricular fibrosis as assessed by cardiac magnetic resonance and exercise capacity after biventricular repair of pulmonary atresia and intact ventricular septum

BACKGROUND

The hypertrophic myocardium, myocardial fiber disarray, and endocardial fibroelastosis in pulmonary atresia and intact ventricular septum (PAIVS) may provide anatomic substrates for restrictive filling of the right ventricle.

HYPOTHESIS

Restrictive right ventricle (RV) physiology is related to RV fibrosis and exercise capacity in patients after biventricular repair of PAIVS.

METHODS

A total of 27 patients, age 16.5 +/- 5.6 years, were recruited after biventricular repair of PAIVS. Restrictive RV physiology was defined by the presence of antegrade diastolic pulmonary flow and RV fibrosis assessed by late gadolinium enhancement (LGE) cardiac magnetic resonance. Their RV function was compared with that of 27 healthy controls and related to RV LGE score and exercise capacity.

RESULTS

Compared with controls, PAIVS patients had lower tricuspid annular systolic and early diastolic velocities, RV global longitudinal systolic strain, systolic strain rate, and early and late diastolic strain rates (all P < 0.05). A total of 22 (81%, 95% confidence interval: 62%-94%) PAIVS patients demonstrated restrictive RV physiology. Compared to those without restrictive RV physiology (n = 5), these 22 patients had lower RV global systolic strain, lower RV systolic and early diastolic strain rates, higher RV LGE score, and a greater percent of predicted maximum oxygen consumption (all P < 0.05).

CONCLUSION

Restrictive RV physiology reflects RV diastolic dysfunction and is associated with more severe RV fibrosis but better exercise capacity in patients after biventricular repair of PAIVS.

The validity, reliability and clinical utility of the Hong Kong Montreal Cognitive Assessment (HK-MoCA) in patients with cerebral small vessel disease

BACKGROUND/AIMS

To evaluate the psychometric properties of the Hong Kong Montreal Cognitive Assessment (HK-MoCA) in patients with cerebral small vessel disease (SVD).

METHODS

40 SVD patients and 40 matched controls were recruited. Concurrent and criterion validity, inter-rater and test-retest reliability, internal consistency of the HK-MoCA were examined and clinical observations were made.

RESULTS

Performance on the HK-MoCA was significantly predicted by both executive (beta = 0.23, p = 0.013) and non-executive (beta = 0.64, p < 0.001) composite scores. It differentiated SVD patients from controls (area under the curve = 0.81, p < 0.001) with an optimal cutoff at 21/22. Reliability, internal consistency and clinical utility were good.

CONCLUSION

The HK-MoCA is a useful cognitive screening instrument for use in SVD patients.

Myocardial T2 quantitation in patients with iron overload at 3 Tesla

PURPOSE

To investigate the feasibility of measuring myocardial T2 at 3 Tesla for assessment of tissue iron in thalassemia major and other iron overloaded patients.

MATERIALS AND METHODS

A single-breathhold electrocardiogram-triggered black-blood multi-echo spin-echo (MESE) sequence with a turbo factor of 2 was implemented at 3 Tesla (T). Myocardial and liver T2 values were measured with three repeated breathholds in 8 normal subjects and 24 patients. Their values, together with the T2 values measured using a breathhold multi-echo gradient-echo sequence, were compared with those at 1.5T in the same patients.

RESULTS

At 3T, myocardial T2 was found to be 39.6 +/- 7.4 ms in normal subjects. In patients, it ranged from 12.9 to 50.1 ms. "T2 and T2(*) [corrected] were observed to correlate in heart (rho = 0.93, P [corrected] < 0.0001) and liver (rho = 0.95, P < 0.0001). Myocardial T2 and T2 at 3T were also highly correlated with the 1.5T measurements. Preliminary results indicated that myocardial T2 quantitation was relatively insensitive to B1 variation, and reproducible with 3.2% intra-exam and 3.8% inter-exam variations.

CONCLUSION

Myocardial T2 quantitation is feasible at 3T. Given the substantially decreased T2 and increased B0 inhomogeneity, the rapid myocardial T2 measurement protocol demonstrated here may present a robust alternative to study cardiac iron overload at 3T.

Long-term prognosis of Chinese patients with a lacunar infarct associated with small vessel disease: a five-year longitudinal study

RATIONALE

Lacunar infarct associated with small vessel disease is a common stroke subtype in China and has a favorable short-term prognosis. Data on its long-term prognosis among Chinese patients are lacking.

AIMS

We aimed to study its long-term prognosis and predictors for poor outcomes.

DESIGN

We followed up to 75 consecutive Chinese stroke patients who had a lacunar infarct for a period of 5 years. Clinical outcomes with respect to mortality and recurrent stroke were noted. We evaluated baseline clinical and imaging predictors for such outcomes using the Cox regression analysis.

STUDY OUTCOMES

Sixteen (21.3%) patients died and 12 (16%) patients had recurrent stroke during follow-up. Twenty-one (28%) patients had combined events of either death and/or recurrent stroke. Univariate Cox regression analysis showed that age, literacy, National Institute of Health Stroke Scale, incident stroke/transient ischemic attack, and white matter lesion volume predicted survival, while, age, National Institute of Health Stroke Scale, systolic blood pressure, hyperhomocysteinemia, silent lacunes, microbleeds, and white matter lesion volume predicted recurrent stroke. Multivariate Cox regression analysis showed that National Institute of Health Stroke Scale (HR 1.25, 95% CI 1.05-1.48) and white matter lesion volume (HR 1.46, 95% CI 1.11-1.92) predicted combined events of mortality and/or recurrent stroke after age adjustment.

CONCLUSION

Approximately one in four patients either died and/or had recurrent stroke within 5 years after a lacunar infarct. Age, stroke severity, and volume of white matter lesion predict a poor long-term prognosis.

Statins for asymptomatic middle cerebral artery stenosis: The Regression of Cerebral Artery Stenosis study

BACKGROUND

The progression of cerebral atherosclerosis increases the risk of stroke and vascular events. Given the known benefits of statins in retarding coronary and carotid atherosclerosis progression, we studied the effects of statins on asymptomatic middle cerebral artery (MCA) stenosis progression.

METHODS

We conducted a randomized, double-blind, placebo-controlled study to evaluate the effects of simvastatin on the progression of MCA stenosis among stroke-free individuals who had mild to moderately elevated LDL cholesterol (3.0-5.0 mmol/l). Two hundred and twenty-seven subjects were randomized to either placebo (n = 114) or simvastatin 20 mg daily (n = 113). The severity of MCA stenosis at baseline and at the end of the study was graded by MRA into normal, minimal (<10%), mild (10-49%), moderate (50-90%) and severe (>90%). The primary outcome was the change in grading of MCA stenosis over 2 years.

RESULTS

At the end of the study, the LDL cholesterol level decreased by 1.43 and 0.12 mmol/l for the active and placebo groups, respectively (p < 0.001). There was no significant difference in the proportion of patients having stable, progressive and regressive MCA stenosis between the placebo (72, 22 and 6%) and active groups (78.6, 15.5 and 5.8%). The all-cause mortality was significantly lower in the active group (n = 0) relative to the placebo group (n = 7, p = 0.014). Any clinical events were also lower in the active group (n = 5) than in the placebo group (n = 13, p = 0.052).

CONCLUSIONS

Simvastatin 20 mg daily had no apparent effect upon the evolution of asymptomatic MCA stenosis over 2 years.

Organ-specific hemosiderosis and functional correlation in Chinese patients with thalassemia intermedia and hemoglobin H disease

We performed MRI assessment in 37 adult Chinese patients with thalassemia intermedia and hemoglobin H disease. Despite abnormal ferritin and liver T2*, only 5% of patients had cardiac hemosiderosis. The two patients with reduced ejection fraction had normal cardiac T2*. Half of the cases showed pituitary and pancreatic iron loading. Subclinical endocrine abnormalities (HOMA, insulin growth factor) showed correlation with pancreatic, pituitary, and cardiac MRI values. Prospective data with serial functional and imaging monitoring is needed to verify the utility for chelation to improve cardiac and endocrine function in this group of patients.

Left ventricular systolic dyssynchrony is a predictor of cardiac remodeling after myocardial infarction

OBJECTIVES

We sought to determine whether early assessment of left ventricular (LV) dyssynchrony by tissue Doppler imaging may predict progressive ventricular enlargement and cardiac dysfunction after acute myocardial infarction (MI).

METHODS

Forty-seven patients (mean age 59.9 +/- 11.6 years) with normal QRS duration underwent tissue Doppler imaging and contrast-enhanced cardiac magnetic resonance imaging (Ce-MRI) at days 2 to 6, 3 months, and at 1 year after the index MI. Systolic dyssynchrony index (Ts-SD) was calculated from 12 LV segments, and infarct size (IS) by Ce-MRI.

RESULTS

The remodeling group (n = 16) (defined as an increase in end-systolic volume > or =10% between 1 year and baseline) had greater initial IS (27.2 +/- 9.6 vs 13.7 +/- 4.1%, P < .001) and Ts-SD (50.9 +/- 12.8 vs 33.6 +/- 7.7 milliseconds, P < .001) than nonremodeling group (n = 31). At 1 year, the remodeling group had progressive increase in Ts-SD and decrease in LV ejection fraction (57.3 +/- 18.5 and 36.0 +/- 7.6%, respectively; both P < .05 vs baseline). Both Ts-SD (odds ratio 1.19 [1.07-1.32], P = .001) and IS (odds ratio 1.65 [1.19-2.29], P = .003) were shown to be independent predictors of progressive LV remodeling. A cutoff value of Ts-SD > or =45 milliseconds predicted LV remodeling at 1 year (sensitivity 90.5%, specificity 90.9%, Area-under-curve 0.907) (P = .0005).

CONCLUSIONS

Left ventricular systolic dyssynchrony is a newly identified predictor of chronic LV remodeling after acute MI, which is independent and incremental to conventional assessment and IS as measured by Ce-MRI.

Characterisation of brain disorders and evaluation of therapy by functional and molecular magnetic resonance techniques

OBJECTIVES

To review advanced functional and molecular magnetic resonance techniques that are currently clinically useful or with potential clinical use in the near future.

DATA SOURCES AND EXTRACTION

Literature search of Medline to December 2007 was conducted. Key words search terms were: 'magnetic resonance imaging', 'magnetic resonance spectroscopy', 'brain', 'functional', 'perfusion', 'diffusion', 'diffusion tensor', 'magnetic transfer', 'molecular imaging', 'superparamagnetic iron oxide'. Relevant original papers and review articles were retrieved.

STUDY SELECTION

A total of 83 original papers and review articles were systematically analysed.

DATA SYNTHESIS

The introduction of modern neuroimaging modalities in recent years has revolutionised investigation of the normal and diseased brain. Among others, magnetic resonance has emerged as the pre-eminent imaging modality, which can produce both high-resolution anatomical images and maps that reflect a variety of physiological parameters relevant to functional assessment and tissue characterisation. Magnetic resonance imaging techniques are now capable of visualising physiological and diseased processes at cellular and molecular levels, including cerebral blood flow, capillary perfusion and permeability, blood oxygenation level-dependent neuronal activation, microscopical motion of water (water diffusion), integrity of axonal fibres, and the molecular transfer of magnetisation within tissues. Magnetic resonance cell trafficking can evaluate the macrophage activity in areas of brain inflammation. Magnetic resonance cell-labelling strategies can be used to monitor the seeding and migration of embryonic stem cells. Magnetic resonance spectroscopy allows the detection of various metabolites that pertain to different biochemical processes in brain tissues. Such metabolites/spectra include: N-acetyl aspartate used as a neuronal marker, choline as a cell membrane metabolism marker, myo-inositol as a glial marker in proton spectrum, and phosphorous whose spectrum provides an in-vivo assessment of the bio-energetic status of tissues. Besides characterisation of brain disorders, magnetic resonance imaging and spectroscopy can improve the planning and monitoring of therapy and contribute to the development of new therapies.

CONCLUSION

Advances in neuroimaging have made a great leap in the morphological, metabolic, and functional assessment of the neurological diseases, enabling better diagnosis and management of patients.