Assessment of Pulmonary Perfusion With Breath-Hold and Free-Breathing Dynamic Contrast-Enhanced Magnetic Resonance Imaging: Quantification and Reproducibility

Retrospectively gated ultrashort-echo-time MRI T1 mapping reveals compromised pulmonary microvascular NO-dependent function in a murine model of acute lung injury

This study sought to develop noninvasive, in vivo imaging schemes that allow for quantitative assessment of pulmonary microvascular functional status based on the combination of pulmonary T1 mapping and dynamic contrast-enhanced (DynCE) imaging. Ultrashort-echo-time (UTE) imaging at 9.4 T of lung parenchyma was performed. Retrospective gating was based on modulation of the first point in each recorded spoke. T1 maps were obtained using a series of five consecutive images with varying RF angles and analyzed with the variable flip angle approach. The obtained mean T1 lung value of 1078 ± 38 ms correlated well with previous reports. Improved intersession variability was observed, as evident from a decreased standard deviation of motion-resolved T1 mapping (F-test = 0.051). Animals received lipopolysaccharide (LPS) and were imaged at t = 2, 6, and 12 h after administration. The nitric oxide (NO)-dependent function was assessed according to changes in lung T1 after L-NAME injection, while microvascular perfusion and oxidant stress were assessed with contrast-enhanced imaging after injection of gadolinium or 3-carbamoyl-proxyl nitroxide radical, respectively. Retrospectivel gated UTE allowed robust, motion-compensated imaging that could be used for T1 mapping of lung parenchyma. Changes in lung T1 after L-NAME injection indicated that LPS induced overproduction of NO at t = 2 and 6 h after LPS, but NO-dependent microvascular function was impaired at t = 12 h after LPS. DynCE imaging at t = 6 h after LPS injection revealed decreased microvascular perfusion, with increased vascular permeability and oxidant stress. MRI allows to visualize and quantify lung microvascular NO-dependent function and its concomitant impairment during acute respiratory distress syndrome development with high sensitivity. UTE T1 mapping appears to be sensitive and useful in probing pulmonary microvascular functional status.

Role of pulmonary perfusion magnetic resonance imaging for the diagnosis of pulmonary hypertension: A review

Among five types of pulmonary hypertension, chronic thromboembolic pulmonary hypertension (CTEPH) is the only curable form, but prompt and accurate diagnosis can be challenging. Computed tomography and nuclear medicine-based techniques are standard imaging modalities to non-invasively diagnose CTEPH, however these are limited by radiation exposure, subjective qualitative bias, and lack of cardiac functional assessment. This review aims to assess the methodology, diagnostic accuracy of pulmonary perfusion imaging in the current literature and discuss its advantages, limitations and future research scope.

A dual center and dual vendor comparison study of automated perfusion-weighted phase-resolved functional lung magnetic resonance imaging with dynamic contrast-enhanced magnetic resonance imaging in patients with cystic fibrosis

For sensitive diagnosis and monitoring of pulmonary disease, ionizing radiation-free imaging methods are of great importance. A noncontrast and free-breathing proton magnetic resonance imaging (MRI) technique for assessment of pulmonary perfusion is phase-resolved functional lung (PREFUL) MRI. Since there is no validation of PREFUL MRI across different centers and scanners, the purpose of this study was to compare perfusion-weighted PREFUL MRI with the well-established dynamic contrast-enhanced (DCE) MRI across two centers on scanners from two different vendors. Sixteen patients with cystic fibrosis (CF) (Center 1: 10 patients; Center 2: 6 patients) underwent PREFUL and DCE MRI at 1.5T in the same imaging session. Normalized perfusion-weighted values and perfusion defect percentage (QDP) values were calculated for the whole lung and three central slices (dorsal, central, ventral of the carina). Obtained parameters were compared using Pearson correlation, Spearman correlation, Bland-Altman analysis, Wilcoxon signed-rank test, and Wilcoxon rank-sum test. Moderate-to-strong correlations between normalized perfusion-weighted PREFUL and DCE values were found (posterior slice: r = 0.69, p < 0.01). Spatial overlap of PREFUL and DCE QDP maps showed an agreement of 79.4% for the whole lung. Further, spatial overlap values of Center 1 were not significantly different to those of Center 2 for the three central slices (p > 0.07). The feasibility of PREFUL MRI across two different centers and two different vendors was shown in patients with CF and obtained results were in agreement with DCE MRI.

Evaluation of Dynamic Contrast-Enhanced MRI Measures of Lung Congestion and Endothelial Permeability in Heart Failure: A Prospective Method Validation Study

Background

Methods for accurate quantification of lung fluid in heart failure (HF) are needed. Dynamic contrast‐enhanced (DCE)‐MRI may be an appropriate modality.

Purpose

DCE‐MRI evaluation of fraction of fluid volume in the interstitial lung space (v_e) and vascular permeability (K^trans).

Study Type

Prospective, single‐center method validation.

Population

Seventeen evaluable healthy volunteers (HVs), 12 participants with HF, and 3 with acute decompensated HF (ADHF).

Field Strength/Sequence

T₁ mapping (spoiled gradient echo variable flip angle acquisition) followed by dynamic series (three‐dimensional spoiled gradient‐recalled echo acquisitions [constant echo time, repetition time, and flip angle at 1.5 T]).

Assessment

Three whole‐chest scans were acquired: baseline (Session 1), 1‐week later (Session 2), following exercise (Session 3). Extended Tofts model quantified v_e and K^trans (voxel‐wise basis); total lung median measures were extracted and fitted via repeat measure analysis of variance (ANOVA) model. Patient tolerability of the scanning protocol was assessed.

Statistical Tests

This was constructed as an experimental medicine study. Primary endpoints: K^trans and v_e at baseline (HV vs. HF), change in K^trans and v_e following exercise, and following lung congestion resolution (ADHF). K^trans and v_e were fitted separately using ANOVA. Secondary endpoint: repeatability, that is, within‐participant variability in v_e and K^trans between sessions (coefficient of variation estimated via mixed effects model).

Results

There was no significant difference in mean K^trans between HF and HV (P ≤ 0.17): 0.2216 minutes⁻¹ and 0.2353 minutes⁻¹ (Session 1), 0.2044 minutes⁻¹ and 0.2567 minutes⁻¹ (Session 2), 0.1841 minutes⁻¹ and 0.2108 minutes⁻¹ (Session 3), respectively. v_e was greater in the HF group (all scans, P ≤ 0.02). Results were repeatable between Sessions 1 and 2; mean values for HF and HV were 0.4946 and 0.3346 (Session 1), 0.4353 and 0.3205 (Session 2), respectively. There was minimal difference in K^trans or v_e between scans for participants with ADHF (small population precluded significance testing). Scanning was well tolerated.

Data Conclusion

While no differences were detected in K^trans, v_e was greater in chronic HF patients vs. HV, augmented beyond plasma and intracellular volume. DCE‐MRI is a valuable diagnostic and physiologic tool to evaluate changes in fluid volume in the interstitial lung space associated with symptomatic HF.

Level of Evidence

2

Technical Efficacy Stage

2

Integrated Cardiopulmonary MRI Assessment of Pulmonary Hypertension

Pulmonary hypertension (PH) is a heterogeneous condition that can affect the lung parenchyma, pulmonary vasculature, and cardiac chambers. Accurate diagnosis often requires multiple complex assessments of the cardiac and pulmonary systems. MRI is able to comprehensively assess cardiac structure and function, as well as lung parenchymal, pulmonary vascular, and functional lung changes. Therefore, MRI has the potential to provide an integrated functional and structural assessment of the cardiopulmonary system in a single exam. Cardiac MRI is used in the assessment of PH in most large PH centers, whereas lung MRI is an emerging technique in patients with PH. This article reviews the current literature on cardiopulmonary MRI in PH, including cine MRI, black-blood imaging, late gadolinium enhancement, T₁ mapping, myocardial strain analysis, contrast-enhanced perfusion imaging and contrast-enhanced MR angiography, and hyperpolarized gas functional lung imaging. This article also highlights recent developments in this field and areas of interest for future research including cardiac MRI-based diagnostic models, machine learning in cardiac MRI, oxygen-enhanced ¹ H imaging, contrast-free ¹ H perfusion and ventilation imaging, contrast-free angiography and UTE imaging. EVIDENCE LEVEL: 5 TECHNICAL EFFICACY: Stage 3.

Quantification of pulmonary perfusion in idiopathic pulmonary fibrosis with first pass dynamic contrast-enhanced perfusion MRI

Introduction

Idiopathic pulmonary fibrosis (IPF) is a fatal disease of lung scarring. Many patients later develop raised pulmonary vascular pressures, sometimes disproportionate to the interstitial disease. Previous therapeutic approaches that have targeted pulmonary vascular changes have not demonstrated clinical efficacy, and quantitative assessment of regional pulmonary vascular involvement using perfusion imaging may provide a biomarker for further therapeutic insights.

Methods

We studied 23 participants with IPF, using dynamic contrast-enhanced MRI (DCE-MRI) and pulmonary function tests, including forced vital capacity (FVC), transfer factor (TL_CO) and coefficient (K_CO) of the lungs for carbon monoxide. DCE-MRI parametric maps were generated including the full width at half maximum (FWHM) of the bolus transit time through the lungs. Key metrics used were mean (FWHM_mean) and heterogeneity (FWHM_IQR). Nineteen participants returned at 6 months for repeat assessment.

Results

Spearman correlation coefficients were identified between TL_CO and FWHM_IQR (r=−0.46; p=0.026), K_CO and FWHM_mean (r=−0.42; p=0.047) and K_CO and FWHM_IQR (r=−0.51; p=0.013) at baseline. No statistically significant correlations were seen between FVC and DCE-MRI metrics. Follow-up at 6 months demonstrated statistically significant decline in FVC (p=0.040) and K_CO (p=0.014), with an increase in FWHM_mean (p=0.040), but no significant changes in TL_CO (p=0.090) nor FWHM_IQR (p=0.821).

Conclusions

DCE-MRI first pass perfusion demonstrates correlations with existing physiological gas exchange metrics, suggesting that capillary perfusion deficit (as well as impaired interstitial diffusion) may contribute to gas exchange limitation in IPF. FWHM_mean showed a significant increase over a 6-month period and has potential as a quantitative biomarker of pulmonary vascular disease progression in IPF.

Measurement Variability in Treatment Response Determination for Non-Small Cell Lung Cancer: Improvements Using Radiomics

Multimodality imaging measurements of treatment response are critical for clinical practice, oncology trials, and the evaluation of new treatment modalities. The current standard for determining treatment response in non-small cell lung cancer (NSCLC) is based on tumor size using the RECIST criteria. Molecular targeted agents and immunotherapies often cause morphological change without reduction of tumor size. Therefore, it is difficult to evaluate therapeutic response by conventional methods. Radiomics is the study of cancer imaging features that are extracted using machine learning and other semantic features. This method can provide comprehensive information on tumor phenotypes and can be used to assess therapeutic response in this new age of immunotherapy. Delta radiomics, which evaluates the longitudinal changes in radiomics features, shows potential in gauging treatment response in NSCLC. It is well known that quantitative measurement methods may be subject to substantial variability due to differences in technical factors and require standardization. In this review, we describe measurement variability in the evaluation of NSCLC and the emerging role of radiomics.

A framework for Fourier-decomposition free-breathing pulmonary 1 H MRI ventilation measurements

PURPOSE

To develop a rapid Fourier decomposition (FD) free-breathing pulmonary ¹ H MRI (FDMRI) image processing and biomarker pipeline for research use.

METHODS

We acquired MRI in 20 asthmatic subjects using a balanced steady-state free precession (bSSFP) sequence optimized for ventilation imaging. 2D ¹ H MRI series were segmented by enforcing the spatial similarity between adjacent images and the right-to-left lung volume-ratio. The segmented lung series were co-registered using a coarse-to-fine deformable registration framework that used dual optimization techniques. All pairwise registrations were implemented in parallel and FD was performed to generate 2D ventilation-weighted maps and ventilation-defect-percent (VDP). Lung segmentation and registration accuracy were evaluated by comparing algorithm and manual lung-masks, deformed manual lung-masks, and fiducials in the moving and fixed images using Dice-similarity-coefficient (DSC), mean-absolute-distance (MAD), and target-registration-error (TRE). The relationship of FD-VDP and ³ He-VDP was evaluated using the Pearson-correlation-coefficient (r) and Bland Altman analysis. Algorithm reproducibility was evaluated using the coefficient-of-variation (CoV) and intra-class-correlation-coefficient (ICC) for segmentation, registration, and FD-VDP components.

RESULTS

For lung segmentation, there was a DSC of 95 ± 1.5% and MAD of 2.3 ± 0.5 mm, and for registration there was a DSC of 97 ± 0.8%, MAD of 1.6 ± 0.4 mm and TRE of 3.6 ± 1.2 mm. Reproducibility for segmentation DSC (CoV/ICC = 0.5%/0.92), registration TRE (CoV/ICC = 0.4%/0.98), and FD-VDP (Cov/ICC = 3.9%/0.97) was high. The pipeline required 10 min/subject. FD-VDP was correlated with ³ He-VDP (r = 0.69, P < 0.001) although there was a bias toward lower FD-VDP (bias = -4.9%).

CONCLUSIONS

We developed and evaluated a pipeline that provides a rapid and precise method for FDMRI ventilation maps.

Emphysema and lung volume reduction: the role of radiology

Chronic obstructive pulmonary disease (COPD) is one of the leading causes of death worldwide. One of the main findings is pulmonary emphysema in association with chronic bronchitis. Clinical signs, pulmonary function tests and imaging are the current used methods to diagnose and stage emphysema. Lung volume reduction (LVR) and endoscopic lung volume reduction (ELVR) are the current therapeutic options beside lung transplantation in cases of severe emphysema. Nowadays imaging is one of the key factors for the success of these therapies. Especially quantitative computed tomography (CT) with its increasing possibilities has become a viable tool, providing detailed information about distribution and heterogeneity of emphysema. Other imaging techniques like dual-energy CT (DECT) and functional magnetic resonance (MR) have shown to add functional information. These structural and functional information support thoracic surgeons and interventional pulmonologists in selecting patients and optimizing LVR procedures but also enables the development of new endobronchial therapies. Imaging will further improve the individual outcome by supporting the choice of optimal therapy.

Time-Resolved Three-Dimensional Contrast-Enhanced Magnetic Resonance Angiography in Patients with Chronic Expanding and Stable Aortic Dissections

Objective

To prospectively evaluate our hypothesis that three-dimensional time-resolved contrast-enhanced magnetic resonance angiography (TR-MRA) is able to detect hemodynamic alterations in patients with chronic expanding aortic dissection compared to stable aortic dissections.

Materials and Methods

20 patients with chronic or residual aortic dissection in the descending aorta and patent false lumen underwent TR-MRA of the aorta at 1.5 T and repeated follow-up imaging (mean follow-up 5.4 years). 7 patients showed chronic aortic expansion and 13 patients had stable aortic diameters. Regions of interest were placed in the nondissected ascending aorta and the false lumen of the descending aorta at the level of the diaphragm (FL-diaphragm level) resulting in respective time-intensity curves.

Results

For the FL-diaphragm level, time-to-peak intensity and full width at half maximum were significantly shorter in the expansion group compared to the stable group (p = 0.027 and p = 0.003), and upward and downward slopes of time-intensity curves were significantly steeper (p = 0.015 and p = 0.005). The delay of peak intensity in the FL-diaphragm level compared to the nondissected ascending aorta was significantly shorter in the expansion group compared to the stable group (p = 0.01).

Conclusions

3D TR-MRA detects significant alterations of hemodynamics within the patent false lumen of chronic expanding aortic dissections compared to stable aortic dissections.

Temporal similarity perfusion mapping: A standardized and model-free method for detecting perfusion deficits in stroke

INTRODUCTION

Interpretation of the extent of perfusion deficits in stroke MRI is highly dependent on the method used for analyzing the perfusion-weighted signal intensity time-series after gadolinium injection. In this study, we introduce a new model-free standardized method of temporal similarity perfusion (TSP) mapping for perfusion deficit detection and test its ability and reliability in acute ischemia.

MATERIALS AND METHODS

Forty patients with an ischemic stroke or transient ischemic attack were included. Two blinded readers compared real-time generated interactive maps and automatically generated TSP maps to traditional TTP/MTT maps for presence of perfusion deficits. Lesion volumes were compared for volumetric inter-rater reliability, spatial concordance between perfusion deficits and healthy tissue and contrast-to-noise ratio (CNR).

RESULTS

Perfusion deficits were correctly detected in all patients with acute ischemia. Inter-rater reliability was higher for TSP when compared to TTP/MTT maps and there was a high similarity between the lesion volumes depicted on TSP and TTP/MTT (r(18) = 0.73). The Pearson's correlation between lesions calculated on TSP and traditional maps was high (r(18) = 0.73, p<0.0003), however the effective CNR was greater for TSP compared to TTP (352.3 vs 283.5, t(19) = 2.6, p<0.03.) and MTT (228.3, t(19) = 2.8, p<0.03).

DISCUSSION

TSP maps provide a reliable and robust model-free method for accurate perfusion deficit detection and improve lesion delineation compared to traditional methods. This simple method is also computationally faster and more easily automated than model-based methods. This method can potentially improve the speed and accuracy in perfusion deficit detection for acute stroke treatment and clinical trial inclusion decision-making.

Magnetic Resonance Imaging for the Evaluation of Pulmonary Embolism

Pulmonary embolism (PE) is a leading cause of acute cardiovascular death throughout the world. Although computed tomography angiography (CTA) is the primary imaging study used to diagnose acute PE, pulmonary magnetic resonance angiography (MRA) is increasingly being used in patients with contraindications for CTA. This manuscript reviews the MRA techniques used for the diagnosis of PE and discuss how these techniques can be implemented in routine clinical practice. In addition, the efficacy and effectiveness of these techniques will be compared to other modalities.

Contrast-enhanced pulmonary MRA for the primary diagnosis of pulmonary embolism: current state of the art and future directions

CT pulmonary angiography (CTPA) is currently considered the imaging standard of care for the diagnosis of pulmonary embolism (PE). Recent advances in contrast-enhanced pulmonary MR angiography (MRA) techniques have led to increased use of this modality for the detection of PE in the proper clinical setting. This review is intended to provide an introduction to the state-of-the-art techniques used in pulmonary MRA for the detection of PE and to discuss possible future directions for this modality. This review discusses the following issues pertinent to MRA for the diagnosis of PE: (1) the diagnostic efficacy and clinical effectiveness for pulmonary MRA relative to CTPA, (2) the different pulmonary MRA techniques used for the detection of PE, (3) guidance for building a clinical service at their institution using MRA and (4) future directions of PE MRA. Our principal aim was to show how pulmonary MRA can be used as a safe, effective modality for the diagnosis of clinically significant PE, particularly for those patients where there are concerns about ionizing radiation or contraindications/allergies to the iodinated contrast material.

Assessment of regional pulmonary blood flow using 68Ga-DOTA PET

Background

In vivo determination of regional pulmonary blood flow (PBF) is a valuable tool for the evaluation of many lung diseases. In this study, the use of ⁶⁸Ga-DOTA PET for the in vivo quantitative determination of regional PBF is proposed. This methodology was implemented and tested in healthy pigs and validated using fluorescent microspheres. The study was performed on young large white pigs (n = 4). To assess the reproducibility and consistency of the method, three PET scans were obtained for each animal. Each radiotracer injection was performed simultaneously to the injection of fluorescent microspheres. PBF images were generated applying a two-compartment exchange model over the dynamic PET images. PET and microspheres values were compared by regression analysis and Bland–Altman plot.

Results

The capability of the proposed technique to produce 3D regional PBF images was demonstrated. The correlation evaluation between ⁶⁸Ga-DOTA PET and microspheres showed a good and significant correlation (r = 0.74, P < 0.001).

Conclusions

Assessment of PBF with the proposed technique allows combining the high quantitative accuracy of PET imaging with the use of ⁶⁸Ga/⁶⁸Ge generators. Thus, ⁶⁸Ga-DOTA PET emerges as a potential inexpensive method for measuring PBF in clinical settings with an extended use.

Electronic supplementary material

The online version of this article (doi:10.1186/s13550-017-0259-2) contains supplementary material, which is available to authorized users.

Magnetic resonance imaging in lung: a review of its potential for radiotherapy

MRI has superior soft-tissue definition compared with existing imaging modalities in radiation oncology; this has the added benefit of functional as well as anatomical imaging. This review aimed to evaluate the current use of MRI for lung cancer and identify the potential of a MRI protocol for lung radiotherapy (RT). 30 relevant studies were identified. Improvements in MRI technology have overcome some of the initial limitations of utilizing MRI for lung imaging. A number of commercially available and novel sequences have shown image quality to be adequate for the detection of pulmonary nodules with the potential for tumour delineation. Quantifying tumour motion is also feasible and may be more representative than that seen on four-dimensional CT. Functional MRI sequences have shown correlation with flu-deoxy-glucose positron emission tomography (FDG-PET) in identifying malignant involvement and treatment response. MRI can also be used as a measure of pulmonary function. While there are some limitations for the adoption of MRI in RT-planning process for lung cancer, MRI has shown the potential to compete with both CT and PET for tumour delineation and motion definition, with the added benefit of functional information. MRI is well placed to become a significant imaging modality in RT for lung cancer.

Comparison of models and contrast agents for improved signal and signal linearity in dynamic contrast-enhanced pulmonary magnetic resonance imaging

OBJECTIVES

The objectives of this study were to compare pulmonary blood flow (PBF) measurements acquired with 3 previously published models (low-dose "single bolus," "dual bolus" and a "nonlinear correction" algorithm) for addressing the nonlinear relationship between contrast agent concentration and magnetic resonance signal in the arterial input function (AIF) and to compare both lung signal and PBF measurements obtained using gadopentetate dimeglumine (Gd-DTPA, Magnevist) with those obtained using the high-relaxivity agent gadobenate dimeglumine (Gd-BOPTA, Multihance).

MATERIALS AND METHODS

Ten of 12 healthy humans were successfully scanned on 2 consecutive days at 1.5 T. Contrast-enhanced pulmonary perfusion scans were acquired with a 3-dimensional spoiled gradient echo pulse sequence and interleaved variable density k-space sampling with a 1-second frame rate and 4 × 4 × 4-mm resolution. Each day, 2 perfusion scans were acquired with either Gd-DTPA or Gd-BOPTA; the order of the administered contrast agent was randomized. Region of interest analysis was used to determine PBF on the basis of the indicator dilution theory. Linear mixed-effects modeling was used to compare the AIF models and contrast agents.

RESULTS

With Gd-DTPA, no significant differences were observed between the mean PBF calculated for the single bolus (323 ± 110 mL/100mL/min), dual bolus (315 ± 177 mL/100mL/min), and nonlinear correction (298 ± 100 mL/100mL/min) approach. With Gd-BOPTA, the mean PBF using the dual bolus approach (245 ± 103 mL/100mL/min) was lower than with the single bolus (345 ± 130 mL/100mL/min P < 0.01) and nonlinear correction (321 ± 115 mL/100mL/min; P = 0.02). Peak lung enhancement was significantly higher in all regions with Gd-BOPTA than with Gd-DTPA (P << 0.01).

CONCLUSIONS

The dual bolus approach with Gd-BOPTA resulted in a significantly lower PBF than did the other combinations of contrast agent and AIF model. No other statistically significant differences were found. Given the much higher signal in the lung parenchyma using Gd-BOPTA, the use of Gd-BOPTA with either single bolus or the nonlinear correction method appears most promising for voxelwise perfusion quantification using 3-dimensional dynamic contrast-enhanced pulmonary perfusion magnetic resonance imaging.

Free breathing contrast-enhanced time-resolved magnetic resonance angiography in pediatric and adult congenital heart disease

BACKGROUND

Contrast enhanced magnetic resonance angiography (MRA) is generally performed during a long breath-hold (BH), limiting its utility in infants and small children. This study proposes a free-breathing (FB) time resolved MRA (TRA) technique for use in pediatric and adult congenital heart disease (CHD).

METHODS

A TRA sequence was developed by combining spiral trajectories with sensitivity encoding (SENSE, x4 kx-ky and x2 kz) and partial Fourier (75% in kz). As no temporal data sharing is used, an independent 3D data set was acquired every ~1.3s, with acceptable spatial resolution (~2.3x2.3x2.3 mm). The technique was tested during FB over 50 consecutive volumes. Conventional BH-MRA and FB-TRA data was acquired in 45 adults and children with CHD. We calculated quantitative image quality for both sequences. Diagnostic accuracy was assessed in all patients from both sequences. Additionally, vessel measurements were made at the sinotubular junction (N = 43), proximal descending aorta (N = 43), descending aorta at the level of the diaphragm (N = 43), main pulmonary artery (N = 35), left pulmonary artery (N = 35) and the right pulmonary artery (N = 35). Intra and inter observer variability was assessed in a subset of 10 patients.

RESULTS

BH-MRA had significantly higher homogeneity in non-contrast enhancing tissue (coefficient of variance, P <0.0001), signal-to-noise ratio (P <0.0001), contrast-to-noise ratio (P <0.0001) and relative contrast (P = 0.02) compared to the FB-TRA images. However, homogeneity in the vessels was similar in both techniques (P = 0.52) and edge sharpness was significantly (P <0.0001) higher in FB-TRA compared to BH-MRA. BH-MRA provided overall diagnostic accuracy of 82%, and FB-TRA of 87%, with no statistical difference between the two sequences (P = 0.77). Vessel diameter measurements showed excellent agreement between the two techniques (r = 0.98, P <0.05), with no bias (0.0 mm, P = 0.71), and clinically acceptable limits of agreement (-2.7 to +2.8 mm). Inter and intra observer reproducibility showed good agreement of vessel diameters (r>0.988, P<0.0001), with negligible biases (between -0.2 and +0.1mm) and small limits of agreement (between -2.4 and +2.5mm).

CONCLUSIONS

We have described a FB-TRA technique that is shown to enable accurate diagnosis and vessel measures compared to conventional BH-MRA. This simplifies the MRA technique and will enable angiography to be performed in children and adults whom find breath-holding difficult.