DCE Acquisition & Reconstruction
Anders Garpebring1

1Department of Radiation Sciences, Umeå University, Umeå, Sweden


This talk will describe the basics of dynamic contrast-enhanced (DCE) MRI with focus on the acquisition of the data. Key prerequisites for accurate quantification of perfusion parameters such as Ktrans are sufficiently high spatial and temporal resolution but also accurate quantification of the contrast agent (CA) concentration. The basics of how this can be achieve will be covered in the talk.


In DCE-MRI a CA is injected intravenously and the uptake and washout is monitored using a high temporal resolution MRI scan that is sensitive to the change in T1 relaxation time caused by the CA (1). From the temporal dynamics, in each voxel or in a region of interest, physiological information can be extracted regarding e.g. blood volume or leakiness of the capillary system (2). Applications are found in several areas, for example assessment of chemoradiotherapy (3). To accurately quantify perfusion parameters, high quality DCE-MRI data is required. However this is difficult to obtain due to several conflicting demands regarding temporal resolution, spatial resolution and accuracy.

Requirements from physiology

The requirements on the imaging is set by the physiology of the imaged subject and the information that is to be extracted from the data. Typically this implies that the kinetics of the CA needs to be monitored for several minutes (up to about 15 min for very slowly enhancing tissues (4)) and a sample is needed at least every 4 seconds [5] for Ktrans quantification. If blood flow and capillary transit time is to be quantified the sampling rate must be even higher and a sampling time of 1.5 s has been suggested [13]. Meeting the temporal requirements would be simple if it were not for the spatial requirements that must be fulfilled simultaneously. In for instance cancer imaging one is often interested in tumor heterogeneity, and not acquiring slices covering all of the tumor/tumors is not a good option since that could lead to information being missed (5), hence both a large imaging field-of-view (FOV) and high spatial resolution are typically desired. Acquiring the blood plasma CA concentration, the arterial input function (AIF), is essential for most analysis of DCE-MRI data. It is also very demanding considering that the AIF changes rapidly, the vessels are usually small and a large FOV might be required if no suitable vessel is close to the investigated site.

Quantifying the contrast agent concentration

Not only is it enough that images can be obtained with sufficient spatio-temporal resolution and FOV, it must also be possible to infer the CA concentration from the images. This implies that the T1 relaxation time must be measured at a very high rate (0.2-1 Hz) in the entire FOV. To achieve this a minimum repetition time 3D spoiled gradient Echo (3D-SPGR) sequence is most often used (6). However, this sequence is T1-weighted and does not in it-self give the T1 time and the CA concentration. For that, additional measurements are required, i.e. a baseline signal and a T1 map without the CA present. The baseline is obtained simply by monitoring the signal before the injection and the T1 map is typically acquired using the variable flip angle (VFA) method (7), also before the injection of CA. The CA concentration estimation is very sensitive to the pre-contrast T1 and unfortunately it has been shown that the SPGR sequence used in DCE-MRI and in the VFA method is sensitive to variations in B1 and also sensitive to the spoiling scheme used (8). This implies that B1 ideally also should be measured, using e.g. actual flip angle imaging (9) or a Bloch-Siegert shift approach (10), in particular at high fields (> 1.5 T). Effects of insufficient spoiling is normally not compensated for, although it is possible by adjusting the signal equation (11).

Measuring the arterial Input function

Measuring the AIF is the most challenging part of DCE-MRI. Not only in terms of spatial and temporal resolution, but also regarding accuracy of the estimated CA concentration. The steady state property of the 3D SPGR sequence implies that CA quantification in flowing blood will fail unless the blood has been flowing for several cm in the imaged region before it reaches the site where the AIF is sampled (11,12). This may increase the required size of the imaged region. An important consideration when setting up a DCE-MRI exam is to determine the flip angle of the 3D SPGR sequence used for CA monitoring. A moderate flip angle around 10° at TR = 5 ms will give a sequence most sensitive to the CA concentration levels in tissue, however, the signal from blood will in this case saturate making it impossible to obtain the AIF. Hence, the use of a measured AIF will require a larger flip angle (around 20°-30°) and this results consequently in a trade-off in the measurement precision in tissue. It may also lead to difficulties with SAR at higher field strengths.

Advanced reconstruction techniques for DCE-MRI

Simultaneously meeting all requirements regarding spatio-temporal resolution and accurate CA quantification without compromises has until recently been impossible. However, with the introduction of compressed sensing (CS) this is changing. Whole brain, high resolution monitoring of CA concentration in DCE-MRI has recently been achieved with a temporal resolution of 4.1 s using CS (13), and CS technology is now becoming available on standard clinical systems. Another interesting development where CS is used is to resolve motion (e.g. XD-GRASP (14)) in free breathing abdominal DCE-MRI. Finally, the latest development with model based DCE-MRI (15) could provide further improvement of the temporal resolution. We are therefore at a very exciting time when no compromises might be needed. This could make it possible to finally reach a long sought goal of standardizing the DCE-MRI data acquisition.


No acknowledgement found.


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Proc. Intl. Soc. Mag. Reson. Med. 26 (2018)