Time-resolved three-dimensional technique for dynamic magnetic resonance dacryocystography.

IMPORTANCE: This study introduces a new technique in the assessment of nasolacrimal drainage with magnetic resonance imaging. BACKGROUND: To describe a new dynamic magnetic resonance dacryocystography (MRDCG) protocol and report normative findings on asymptomatic lacrimal drainage systems. DESIGN: A prospective observational study at the Royal Adelaide Hospital. PARTICIPANTS: Seventeen patients with unilateral epiphora were prospectively recruited. METHODS: Patients underwent dynamic MRDCG. The time-resolved angiography with interleaved stochastic trajectories (TWIST) sequence was used to visualise contrast flow through the lacrimal drainage system. MAIN OUTCOME MEASURES: Tear transit times and anatomical dimensions were measured. RESULTS: Dynamic MRDCG with TWIST sequence reliably demonstrated contrast flow. Tear transit times and anatomical dimensions were comparable to previously reported values in other imaging modalities. CONCLUSIONS AND RELEVANCE: Dynamic MRDCG provides good structural and temporal resolution to the assessment of lacrimal outflow obstructions. The physiological nature of this modality allows potential assessment for functional obstruction and future research on tear flow assessment.

Improved dynamic parallel imaging coil calibration method robust to respiratory motion with application to first-pass contrast-enhanced myocardial perfusion imaging.

PURPOSE: To develop an accurate method of performing free-breathing coil calibration for application to parallel imaging reconstructions of dynamic single-shot datasets. METHODS: Coil calibration data are produced through acquisition of multiple prescans before the accelerated scan, applied during free-breathing. These multiple free-breathing prescans (MFPs) provide the necessary coil information for accurate parallel imaging reconstruction of each accelerated frame of a dynamic series, under guidance of an appropriate respiratory position based matching algorithm. This is investigated in myocardial first-pass perfusion with retrospectively undersampled datasets for analysis with standard calibration techniques to guide prospectively undersampled experiments for specific demonstration of performance against a range of "temporal" calibration techniques. RESULTS: Reconstruction of the retrospectively subsampled datasets with MFP-calibrated parallel imaging showed significant improvements in relative root-mean-square error comparative to all other techniques (all P < 0.05; n = 6) for acceleration factors R > 3. Accelerated acquisitions, reconstructed by means of various temporal calibration techniques and analyzed by visual observer artifact scoring, also demonstrated a large improvement with use of MFPs. Artifact levels were reduced from an average of 2.5 ± 0.6 for the best performing implementation of TGRAPPA to 0.8 ± 0.4 for MFP-GRAPPA (P < 0.001; n = 20) (0 = none to 4 = strong, nondiagnostic). CONCLUSION: MFP as parallel imaging coil calibration data can give improved performance in free-breathing dynamic MR while maintaining maximal acceleration. Magn Reson Med 75:2315-2323, 2016. © 2015 Wiley Periodicals, Inc.

Comparison of 3 T and 1.5 T for T2* magnetic resonance of tissue iron.

BACKGROUND: T2* magnetic resonance of tissue iron concentration has improved the outcome of transfusion dependant anaemia patients. Clinical evaluation is performed at 1.5 T but scanners operating at 3 T are increasing in numbers. There is a paucity of data on the relative merits of iron quantification at 3 T vs 1.5 T. METHODS: A total of 104 transfusion dependent anaemia patients and 20 normal volunteers were prospectively recruited to undergo cardiac and liver T2* assessment at both 1.5 T and 3 T. Intra-observer, inter-observer and inter-study reproducibility analysis were performed on 20 randomly selected patients for cardiac and liver T2*. RESULTS: Association between heart and liver T2* at 1.5 T and 3 T was non-linear with good fit (R (2) = 0.954, p < 0.001 for heart white-blood (WB) imaging; R (2) = 0.931, p < 0.001 for heart black-blood (BB) imaging; R (2) = 0.993, p < 0.001 for liver imaging). R2* approximately doubled between 1.5 T and 3 T with linear fits for both heart and liver (94, 94 and 105 % respectively). Coefficients of variation for intra- and inter-observer reproducibility, as well as inter-study reproducibility trended to be less good at 3 T (3.5 to 6.5 %) than at 1.5 T (1.4 to 5.7 %) for both heart and liver T2*. Artefact scores for the heart were significantly worse with the 3 T BB sequence (median 4, IQR 2-5) compared with the 1.5 T BB sequence (4 [3-5], p = 0.007). CONCLUSION: Heart and liver T2* and R2* at 3 T show close association with 1.5 T values, but there were more artefacts at 3 T and trends to lower reproducibility causing difficulty in quantifying low T2* values with high tissue iron. Therefore T2* imaging at 1.5 T remains the gold standard for clinical practice. However, in centres where only 3 T is available, equivalent values at 1.5 T may be approximated by halving the 3 T tissue R2* with subsequent conversion to T2*.

Validation of T2* in-line analysis for tissue iron quantification at 1.5 T.

BACKGROUND: There is a need for improved worldwide access to tissue iron quantification using T2* cardiovascular magnetic resonance (CMR). One route to facilitate this would be simple in-line T2* analysis widely available on MR scanners. We therefore compared our clinically validated and established T2* method at Royal Brompton Hospital (RBH T2*) against a novel work-in-progress (WIP) sequence with in-line T2* measurement from Siemens (WIP T2*). METHODS: Healthy volunteers (n = 22) and patients with iron overload (n = 78) were recruited (53 males, median age 34 years). A 1.5 T study (Magnetom Avanto, Siemens) was performed on all subjects. The same mid-ventricular short axis cardiac slice and transaxial slice through the liver were used to acquire both RBH T2* images and WIP T2* maps for each participant. Cardiac white blood (WB) and black blood (BB) sequences were acquired. Intraobserver, interobserver and interstudy reproducibility were measured on the same data from a subset of 20 participants. RESULTS: Liver T2* values ranged from 0.8 to 35.7 ms (median 5.1 ms) and cardiac T2* values from 6.0 to 52.3 ms (median 31 ms). The coefficient of variance (CoV) values for direct comparison of T2* values by RBH and WIP were 6.1-7.8 % across techniques. Accurate delineation of the septum was difficult on some WIP T2* maps due to artefacts. The inability to manually correct for noise by truncation of erroneous later echo times led to some overestimation of T2* using WIP T2* compared with the RBH T2*. Reproducibility CoV results for RBH T2* ranged from 1.5 to 5.7 % which were better than the reproducibility of WIP T2* values of 4.1-16.6 %. CONCLUSIONS: Iron estimation using the T2* CMR sequence in combination with Siemens' in-line data processing is generally satisfactory and may help facilitate global access to tissue iron assessment. The current automated T2* map technique is less good for tissue iron assessment with noisy data at low T2* values.

Feasibility of cardiovascular magnetic resonance derived coronary wave intensity analysis.

BACKGROUND: Wave intensity analysis (WIA) of the coronary arteries allows description of the predominant mechanisms influencing coronary flow over the cardiac cycle. The data are traditionally derived from pressure and velocity changes measured invasively in the coronary artery. Cardiovascular magnetic resonance (CMR) allows measurement of coronary velocities using phase velocity mapping and derivation of central aortic pressure from aortic distension. We assessed the feasibility of WIA of the coronary arteries using CMR and compared this to invasive data. METHODS: CMR scans were undertaken in a serial cohort of patients who had undergone invasive WIA. Velocity maps were acquired in the proximal left anterior descending and proximal right coronary artery using a retrospectively-gated breath-hold spiral phase velocity mapping sequence with high temporal resolution (19 ms). A breath-hold segmented gradient echo sequence was used to acquire through-plane cross sectional area changes in the proximal ascending aorta which were used as a surrogate of an aortic pressure waveform after calibration with brachial blood pressure measured with a sphygmomanometer. CMR-derived aortic pressures and CMR-measured velocities were used to derive wave intensity. The CMR-derived wave intensities were compared to invasive data in 12 coronary arteries (8 left, 4 right). Waves were presented as absolute values and as a % of total wave intensity. Intra-study reproducibility of invasive and non-invasive WIA was assessed using Bland-Altman analysis and the intraclass correlation coefficient (ICC). RESULTS: The combination of the CMR-derived pressure and velocity data produced the expected pattern of forward and backward compression and expansion waves. The intra-study reproducibility of the CMR derived wave intensities as a % of the total wave intensity (mean ± standard deviation of differences) was 0.0 ± 6.8%, ICC = 0.91. Intra-study reproducibility for the corresponding invasive data was 0.0 ± 4.4%, ICC = 0.96. The invasive and CMR studies showed reasonable correlation (r = 0.73) with a mean difference of 0.0 ± 11.5%. CONCLUSION: This proof of concept study demonstrated that CMR may be used to perform coronary WIA non-invasively with reasonable reproducibility compared to invasive WIA. The technique potentially allows WIA to be performed in a wider range of patients and pathologies than those who can be studied invasively.

Free-breathing 3D late gadolinium enhancement imaging of the left ventricle using a stack of spirals at 3T.

PURPOSE: To develop navigator-gated free-breathing 3D spiral late gadolinium enhancement (LGE) imaging of the left ventricle at 3T and compare it with conventional breath-hold 2D Cartesian imaging. MATERIALS AND METHODS: Equivalent slices from 3D spiral and multislice 2D Cartesian acquisitions were compared in 15 subjects in terms of image quality (1, nondiagnostic to 5, excellent), sharpness (1-3), and presence of artifacts (0-2). Blood signal-to-noise ratio (SNR), blood/myocardium contrast-to-noise ratio (CNR), and quantitative sharpness were also compared. RESULTS: All 3D spiral scans were completed faster than an equivalent 2D Cartesian short-axis stack (85 vs. 230 sec, P < 0.001). Image quality was significantly higher for 2D Cartesian images than 3D spiral images (3.7 ± 0.87 vs. 3.4 ± 1.05, P = 0.03) but not for mid or apical slices specifically. There were no significant differences in qualitative and quantitative sharpness (95% confidence interval [CI]: 1.91 ± 0.67 vs. 1.93 ± 0.69, P = 0.83 and 95% CI: 0.41 ± 0.07 vs. 0.40 ± 0.09, P = 0.25, respectively), artifact scores (95% CI: 0.16 ± 0.37 vs. 0.40 ± 0.58, P = 0.16), SNR (95% CI: 121.5 ± 55.3 vs. 136.4 ± 77.9, P = 0.13), and CNR (95% CI: 101.6 ± 48.4 vs. 102.7 ± 61.8, P = 0.98). Similar enhancement ratios (0.65 vs. 0.62) and volumes (13.8 vs. 14.1cm(3) ) were measured from scar regions of three patients. CONCLUSIO: Navigator-gated 3D spiral LGE imaging can be performed in significantly and substantially shorter acquisition durations, although with some reduced image quality, than multiple breath-hold 2D Cartesian imaging while providing higher resolution and contiguous coverage.

Validation of high temporal resolution spiral phase velocity mapping of temporal patterns of left and right coronary artery blood flow against Doppler guidewire.

BACKGROUND: Temporal patterns of coronary blood flow velocity can provide important information on disease state and are currently assessed invasively using a Doppler guidewire. A non-invasive alternative would be beneficial as it would allow study of a wider patient population and serial scanning. METHODS: A retrospectively-gated breath-hold spiral phase velocity mapping sequence (TR 19 ms) was developed at 3 Tesla. Velocity maps were acquired in 8 proximal right and 15 proximal left coronary arteries of 18 subjects who had previously had a Doppler guidewire study at the time of coronary angiography. Cardiovascular magnetic resonance (CMR) velocity-time curves were processed semi-automatically and compared with corresponding invasive Doppler data. RESULTS: When corrected for differences in heart rate between the two studies, CMR mean velocity through the cardiac cycle, peak systolic velocity (PSV) and peak diastolic velocity (PDV) were approximately 40 % of the peak Doppler values with a moderate - good linear relationship between the two techniques (R(2): 0.57, 0.64 and 0.79 respectively). CMR values of PDV/PSV showed a strong linear relationship with Doppler values with a slope close to unity (0.89 and 0.90 for right and left arteries respectively). In individual vessels, plots of CMR velocities at all cardiac phases against corresponding Doppler velocities showed a consistent linear relationship between the two with high R(2) values (mean +/-SD: 0.79 +/-.13). CONCLUSIONS: High temporal resolution breath-hold spiral phase velocity mapping underestimates absolute values of coronary flow velocity but allows accurate assessment of the temporal patterns of blood flow.

T1 at 1.5T and 3T compared with conventional T2* at 1.5T for cardiac siderosis.

BACKGROUND: Myocardial black blood (BB) T2* relaxometry at 1.5T provides robust, reproducible and calibrated non-invasive assessment of cardiac iron burden. In vitro data has shown that like T2*, novel native Modified Look-Locker Inversion recovery (MOLLI) T1 shortens with increasing tissue iron. The relative merits of T1 and T2* are largely unexplored. We compared the established 1.5T BB T2* technique against native T1 values at 1.5T and 3T in iron overload patients and in normal volunteers. METHODS: A total of 73 subjects (42 male) were recruited, comprising 20 healthy volunteers (controls) and 53 patients (thalassemia major 22, sickle cell disease 9, hereditary hemochromatosis 9, other iron overload conditions 13). Single mid-ventricular short axis slices were acquired for BB T2* at 1.5T and MOLLI T1 quantification at 1.5T and 3T. RESULTS: In healthy volunteers, median T1 was 1014 ms (full range 939-1059 ms) at 1.5T and modestly increased to 1165ms (full range 1056-1224 ms) at 3T. All patients with significant cardiac iron overload (1.5T T2* values <20 ms) had T1 values <939 ms at 1.5T, and <1056 ms at 3T. Associations between T2* and T1 were found to be moderate with y =377 · x(0.282) at 1.5T (R(2) = 0.717), and y =406 · x(0.294) at 3T (R(2) = 0.715). Measures of reproducibility of T1 appeared superior to T2*. CONCLUSIONS: T1 mapping at 1.5T and at 3T can identify individuals with significant iron loading as defined by the current gold standard T2* at 1.5T. However, there is significant scatter between results which may reflect measurement error, but it is also possible that T1 interacts with T2*, or is differentially sensitive to aspects of iron chemistry or other biology. Hurdles to clinical implementation of T1 include the lack of calibration against human myocardial iron concentration, no demonstrated relation to cardiac outcomes, and variation in absolute T1 values between scanners, which makes inter-centre comparisons difficult. The relative merits of T1 at 3T versus T2* at 3T require further consideration.

Upper airway factors that protect against obstructive sleep apnoea in healthy older males.

The prevalence of obstructive sleep apnoea (OSA) increases with age, yet the risk factors for OSA in older people remain poorly understood. This study aimed to define the age-related changes in upper airway morphology in carefully matched groups of healthy older (>60 years, n=11) and younger (<40 years, n=14) males, using direct (magnetic resonance imaging (MRI)) and indirect (acoustic reflection) imaging. The median (interquartile range) combined retropalatal and retroglossal pharyngeal length was greater in older than in younger males (older 8.8 (7.8-9.0) cm, younger 7.8 (7.0-8.3) cm; p=0.03), as was the soft palate cross-sectional area (older 43.1 (36.0-48.8) cm(2), younger 35.3 (30.5-40.5) cm(2); p=0.03), parapharyngeal fat pad diameter (older 1.7 (1.4-2.2) cm, younger 1.2 (1.0-1.8) cm; p=0.03) and cross-sectional area of the fat pads (older 13.8 (9.1-17.1) cm(2); younger 7.4 (5.9-13.0) cm(2); p=0.02) as measured by MRI. Using acoustic reflection, pharyngeal calibre (older 4.8 (3.8-6.6) cm(2), younger 3.4 (2.8-4.6) cm(2); p=0.03), pharyngeal volume (older 35.1 (30.9-55.4) cm(3), younger 27.2 (22.7-44.2) cm(3); p=0.04) and glottis area (older 2.7 (2.1-3.9) cm(2), younger 1.3 (1.1-1.9) cm(2); p=0.003) were also larger in older participants compared with younger participants. There was no difference in craniofacial measures between groups, including volumetric data and hyoid bone position. The larger pharyngeal calibre observed in older males may be compensating for an age-related enlargement in pharyngeal soft tissue that predisposes to OSA.

Navigator artifact reduction in three-dimensional late gadolinium enhancement imaging of the atria.

PURPOSE: Navigator-gated three-dimensional (3D) late gadolinium enhancement (LGE) imaging demonstrates scarring following ablation of atrial fibrillation. An artifact originating from the slice-selective navigator-restore pulse is frequently present in the right pulmonary veins (PVs), obscuring the walls and making quantification of enhancement difficult. We describe a simple sequence modification to greatly reduce or remove this artifact. METHODS: A navigator-gated inversion-prepared gradient echo sequence was modified so that the slice-selective navigator-restore pulse was delayed in time from the nonselective preparation (NAV-restore-delayed). Both NAV-restore-delayed and conventional 3D LGE acquisitions were performed in 11 patients and the results compared. RESULTS: One patient was excluded due to severe respiratory motion artifact in both NAV-restore-delayed and conventional acquisitions. Moderate to severe artifact was present in 9 of the remaining 10 patients using the conventional sequence and was considerably reduced when using the NAV-restore-delayed sequence (ostial PV to blood pool ratio, 1.7 ± 0.5 versus 1.1 ± 0.2, respectively [P < 0.0001]; qualitative artifact scores, 2.8 ± 1.1 versus 1.2 ± 0.4, respectively [P < 0.001]). While navigator signal-to-noise ratio was reduced with the NAV-restore-delayed sequence, respiratory motion compensation was unaffected. CONCLUSIONS: Shifting the navigator-restore pulse significantly reduces or eliminates navigator artifact. This simple modification improves the quality of 3D LGE imaging and potentially aids late enhancement quantification in the atria.

Improved respiratory efficiency of 3D late gadolinium enhancement imaging using the continuously adaptive windowing strategy (CLAWS).

PURPOSE: Acquisition durations of navigator-gated high-resolution three-dimensional late gadolinium enhancement studies may typically be up to 10 min, depending on the respiratory efficiency and heart rate. Implementation of the continuously adaptive windowing strategy (CLAWS) could increase respiratory efficiency, but the resulting non-smooth k-space acquisition order during gadolinium wash-out could result in increased artifact. METHODS: Navigator-gated three-dimensional late gadolinium enhancement acquisitions were performed in 18 patients using tracking end-expiratory accept/reject (EE-ARA) and CLAWS algorithms in random order. RESULTS: Retrospective analysis of the stored navigator data shows that CLAWS scan times are very close to (within 1%) or equal to the fastest achievable scan times while EE-ARA significantly extends the acquisition duration (P < 0.0001). EE-ARA acquisitions are 26% longer than CLAWS acquisitions (378 ± 104 s compared to 301 ± 85 s, P = 0.002). Image quality scores for CLAWS and EE-ARA acquisitions are not significantly different (4.1 ± 0.6 compared to 4.3 ± 0.6, P = ns). Numerical phantom simulations show that the non-uniform k-space ordering introduced by CLAWS results in slight, but not statistically significant, reductions in both blood signal-to-noise ratio (10%) and blood-myocardium contrast-to-noise ratio (12%). CONCLUSIONS: CLAWS results in markedly reduced acquisition durations compared to EE-ARA without significant detriment to the image quality.

A Pilot Study of Dynamic Magnetic Resonance Dacryocystography Imaging to Assess Functional Epiphora.

OBJECTIVE: To evaluate dynamic magnetic resonance dacryocystography (MRDCG) in eyes with functional epiphora. METHODS: We included prospective eyes with epiphora if no alternative cause was found on clinical examination, were patent on syringing, had no obstruction or stenosis on DCG, and had an abnormal DSG. MRDCG was performed to qualitatively assess for block or patency and quantitatively measure tear transit time. We compared measurements to asymptomatic fellow eyes and to historical reference values from asymptomatic eyes. RESULTS: We included 26 symptomatic eyes of 19 patients (median age 63 years). There was a block on MRDCG in 18 (69%) eyes and patency in 8 (31%) eyes. The block occurred at the sac-nasolacrimal duct (NLD) junction in 9 (50%), proximal NLD in 5 (28%), mid-NLD in 1 (5.6%), and distal NLD in 1 (5.6%) eye(s). No contrast was observed in the lacrimal system in two eyes. For eyes patent on MRDCG, median times to the sac, NLD, inferior meatus, first 25%, and first 50% of the fundus-to-nose distance (FND) were 22, 54, 118, 34, and 84 s, respectively. Times to the sac, NLD, and to fill the first 25% and 50% of the FND were significantly longer than historical values from asymptomatic lacrimal systems (p = 0.017, 0.050, 0.035, 0.017, respectively). CONCLUSION: MRDCG shows a high rate of block in functional epiphora. However, DSG and MRDCG results may not always correlate. The improved temporal resolution of this emerging modality may be advantageous in the critical first 2 min of tear transit.

Cardiovascular magnetic resonance: Diagnostic utility and specific considerations in the pediatric population.

Cardiovascular magnetic resonance is a non-invasive imaging modality which is emerging as important tool for the investigation and management of pediatric cardiovascular disease. In this review we describe the key technical and practical differences between scanning children and adults, and highlight some important considerations that must be taken into account for this patient population. Using case examples commonly seen in clinical practice, we discuss the important clinical applications of cardiovascular magnetic resonance, and briefly highlight key future developments in this field.

Atherosclerosis is Evident in Treated HIV-Infected Subjects With Low Cardiovascular Risk by Carotid Cardiovascular Magnetic Resonance.

OBJECTIVE: Premature atherosclerosis has been observed among HIV-infected individuals with high cardiovascular risk using one-dimensional ultrasound carotid intima-media thickness. We evaluated the assessment of HIV-infected individuals with low traditional cardiovascular disease risk using cardiovascular magnetic resonance, which allows three-dimensional assessment of the carotid artery wall. METHODS: Carotid cardiovascular magnetic resonance was performed in 33 HIV-infected individuals (cases) (19 male, 14 female), and 35 HIV-negative controls (20 male, 15 female). Exclusion criteria included smoking, hypertension, hyperlipidemia (total cholesterol/HDL ratio > 5) or family history of premature atherosclerosis. Cases were stable on combination antiretroviral therapy with plasma HIV-1 RNA <50 copies per milliliter. Using computer modeling, the arterial wall, lumen, and total vessel volumes were calculated for a 4-cm length of each carotid artery centered on the bifurcation. The wall/outer-wall ratio (W/OW), an index of vascular thickening, was compared between the groups. RESULTS: Cases had a median CD4 cell count of 690 cells per microliter. Mean (±SD) age and 10-year Framingham coronary risk scores were similar for cases and controls (45.2 ± 9.7 years versus 46.9 ± 11.6 years and 3.97% ± 3.9% versus 3.72% ± 3.5%, respectively). W/OW was significantly increased in cases compared with controls (36.7% versus 32.5%, P < 0.0001); this was more marked in HIV-infected females. HIV status was significantly associated with increased W/OW after adjusting for age (P < 0.0001). No significant association between antiretroviral type and W/OW was found-W/OW lowered comparing abacavir to zidovudine (P = 0.038), but statistical model fits poorly. CONCLUSIONS: In a cohort of treated HIV-infected individuals with low measurable cardiovascular risk, we have observed evidence of premature subclinical atherosclerosis.

Using GIS and historical records to reconstruct residential exposure to large-scale pesticide application.

Investigation of pesticide impacts on human health depends on good measures of exposure. Historical exposure data are needed to study health outcomes, such as cancer, that involve long latency periods, and other outcomes that are a function of the timing of exposure. Environmental or biological samples collected at the time of epidemiologic study may not represent historical exposure levels. To study the relationship between residential exposure to pesticides and breast cancer on Cape Cod, Massachusetts, historical records of pesticide use were integrated into a geographic information system (GIS) to estimate exposures from large-scale pesticide applications between 1948 and 1995. Information on pesticide use for gypsy moth and other tree/vegetative pest control, cranberry bog cultivation, other agriculture, mosquito control, recreational turf management, and rights-of-way maintenance is included in the database. Residents living within or near pesticide use areas may be exposed through inhalation due to drift and volatilization and through dermal contact and ingestion at the time of application or in later years from pesticides that deposit on soil, accumulate in crops, or migrate to groundwater. Procedures were developed to use the GIS to estimate the relative intensity of past exposures at each study subject's Cape Cod addresses over the past 40 years, taking into account local meteorological data, distance and direction from a residence to a pesticide use source area, size of the source area, application by ground-based or aerial methods, and persistent or nonpersistent character of the pesticide applied. The resulting individual-level estimates of relative exposure intensity can be used in conjunction with interview data to obtain more complete exposure assessment in an epidemiologic study. While the database can improve environmental epidemiological studies involving pesticides, it simultaneously illustrates important data gaps that cannot be filled. Studies such as this one have the potential to identify preventable causes of disease and guide public policies.