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

Background Contrast enhanced magnetic resonance angiography (MRA) is generally performed during a long breath-hold (BH), limiting its use in infants and children. Time resolved MR angiography (TRA) often use data sharing techniques, making it is necessary to acquire data during a BH. This study proposes a high-resolution free breathing (FB) TRA sequence for use in adults and children with congenital heart disease (CHD).


Background
Contrast enhanced magnetic resonance angiography (MRA) is generally performed during a long breath-hold (BH), limiting its use in infants and children. Time resolved MR angiography (TRA) often use data sharing techniques, making it is necessary to acquire data during a BH. This study proposes a high-resolution free breathing (FB) TRA sequence for use in adults and children with 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% kz). Total acceleration was 10.7x and enabled acquisition of a high resolution volume (2.3x2.3x2.3mm) every 1.3s with no data sharing. Importantly, this allowed data to be acquired during FB. Conventional BH-MRA and FB-TRA data was acquired in 45 patients with CHD.
Diagnostic accuracy was assessed by 2 evaluators. The diagnosis were compared to those in the clinical CMR report (assessed from the whole CMR examination, including 3D whole heart and selected cine, black blood and flow imaging).
Additionally, we calculated quantitative image quality for both sequences at Ao1 and MPA, using measures of signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), relative contrast (RC) and edge sharpness.

Results
The median age of the patients was 23.1±15.7years (range: 8-80 years, 13 of whom were <18 years old). FB-TRA data was successfully acquired using in all 45 patients.
BH-MRA provided overall diagnostic accuracy of 82%, and FB-TRA of 87%, with no statistical difference between the 2 sequences (P=0.77). The specific ability of the sequences to assess stenosis (N=13) found sensitivities of 62% and 69% for BH-MRA and FB-TRA, respectively (P=0.56), with both having a specificity of 100%. The specific ability of the sequences to assess dilation (N=53) found sensitivities of 98% and 100% for BH-MRA and FB-TRA, respectively (P=0.32), with both having a specificity of 100%.
Example images are shown in figure 1. BH-MRA had significantly higher SNR (P<0.0001), CNR (P<0.0001) and RC (P=0.02) compared to the FB-TRA images. However, edge sharpness was significantly (P<0.0001) higher in FB-TRA compared to BH-MRA.

Conclusions
We have described a FB-TRA technique that has been shown to enable accurate diagnosis and vessel measures compared to conventional BH-MRA. This technique simplifies the MRA technique by eliminating the need for bolus timing, and will enable angiography to be 1 UCL Centre for Cardiovascular Imaging, London, UK Full list of author information is available at the end of the article    http://www.jcmr-online.com/content/17/S1/O65