2.3 Marco Legal
2.3.3 Normas Internacionales de Información Financiera
While breast MRI screening, as currently implemented, has shown great potential for early detection of cancer in women at increased risk of breast cancer, its wide im- plementation remains difficult. This is largely caused by the high costs of MRI itself. In addition, the huge amount of image series produced lengthens the reading time and makes actual mass screening very difficult.
Therefore, several research groups focused on reducing the time required for scan- ning and evaluating breast MRI. Evidence is mounting that shorter protocols, in fact, are just as good for screening as the much lengthier multiparametric protocols that are currently in use. This could potentially increase the access to breast MRI by significantly reducing the cost and time associated with the examination, both the acquisition time and the radiologists reading time.
Several abbreviated protocols were described by different groups of authors52–54,76
(see Table 2.4). In 2014, Christiane Kuhl and coworkers76 presented the first and simplest version of abbreviated breast MRI. The protocol is condensed into one pre- contrast and one post-contrast acquisition. The subsequent generation of subtraction images and maximum intensity projections (MIPs) also renders reading exception- ally fast. Reading time of the MIPs was reported to be below 2 seconds. In their study, it was evaluated whether this abbreviated protocol would be sufficient to
2.7 Abbreviated screening protocols 27
Table 2.3:Examples of screening protocols
First authorref.# Breast MRI protocol Sequence parameters Sardanelli41∗ 1.0 T or 1.5T
1. 3D T1-weighted spoiled gradient echo (1 pre-contrast and 5 post-contrast)
1. Transverse or coronal plane; TR: 13ms, flip angle: 20-30◦;
partition thickness:≤3mm, number of partitions: 40-128; acquisition time up to 120s; pixel size up to 1.4 x 1.4 mm
Kuhl75 1.5T
1. 2D or 3D T-weighted spoiled gradient echo series (1 pre- and≥4 post-contrast)
1. Spatial resolution≤1x1mm (in-plane),≤3 mm (through- plane); acquisition time 120s
2. T2-weighted sequence 2. Spatial resolution≤1x1mm (in-plane),≤3 mm (through- plane)
Total acquisition time 15 min
Emaus9 3T 1. T2-weighted sequence (optional) 1. Acquisition VS≤1.11 x≤1.46 x≤4.00 mm Reconstruction VS≤0.90 x≤0.90 x≤4.00 mm Acquisition time 147-248s
2. DWI sequence 2. Acquisition VS≤2.25x≤2.51 x≤5.00 mm Reconstruction VS≤1.55 x≤1.70 x≤4.00 mm Acquisition time 215-301s, b-values 0, 50 or 150, and 800 s/mm2
3. DCE data sets (a) High spatial resolution
pre-contrast
(a) Acquisition VS≤1.00 x≤1.00 x≤2.00 mm Reconstruction VS≤1.00 x≤0.94 x≤1.00 mm Acquisition time 80-152s
(b) High temporal resolution series before and during the first seconds after contrast injection
(b) Acquisition VS≤2.58 x≤2.82 x≤6.00 mm Reconstruction VS≤1.18 x≤1.18 x≤3.00 mm Acquisition time 147-248s, pre-contrast acquisitions (N=1), post-contrast acquisitions (N=15-19) (c) High spatial resolution
series
(c) Acquisition VS≤0.90 x≤1.00 x≤1.80 mm Reconstruction VS≤1.00 x≤0.80 x≤1.00 mm Acquisition time 147-248s, acquisitions (N=5-6)
VS; voxel size
∗Although not considered in the final report41(the BI-RADS classification was mainly based on
DCE-imaging), a T2-weighted sequence was also included in the protocol.
identify breast cancer in a screening cohort. The full diagnostic protocol included a T1-weighted pre-contrast and 5 post-contrast scans followed by a T2-weighted se- quence and a coronal T1-weighted sequence. While the full protocol needed about 17 min, the abbreviated protocol needed only 184 seconds. The overall sensitivity of the abbreviated protocol was 100% (negative predictive value 99.8%) with a speci- ficity of 94.3%. However, only 11 cancers were detected overall. With the use of the full diagnostic protocol the characterization of findings classified as possibly benign (BI-RADS 3) was improved, showing that the additional pulse sequences in the full protocol are mainly needed for lesion characterization.
In 2015, Victoria L. Mango and coworkers52looked into the sensitivities per sequence of the abbreviated protocol. They found a mean sensitivity of cancer detection of the first post-contrast sequence of 96%, equal to the first post-contrast subtracted se- quence. Sensitivity using only the MIPs was significantly inferior (93%), which must be taken into account when deciding to screen using only MIPs.
In the same year, Lars J. Grimm and coworkers53 tested two different abbreviated
protocols in a specifically designed case series of 48 patients selected from high-risk screening. One protocol consisted of a T2-weighted sequence, as well as the pre- contrast and the first post-contrast T1-weighted sequences. In the other protocol, the second post-contrast T1-weighted sequence was added to the sequences of the first protocol. They found no significant differences in sensitivity and specificity between each of the two abbreviated protocols (86 and 89%, respectively) and the full proto- col (95%). However, the case series was relatively statistically underpowered while the enriched series (especially the proportion of malignant lesions, much higher than seen in screening practice) could have influenced the reader performance, likely ex- plaining the remarkable low specificity, ranging from 45% to 52%.
In 2016, Laura Heacock and coworkers54 retrospectively evaluated the utility of an
abbreviated T1-weighted imaging protocol in detecting 107 known breast cancers (88% invasive and 12% in situ) as well as to analyze the impact of adding clinical his- tory and prior imaging to cancer detection and determine the impact of T2-weighted imaging in cancer detection and lesion conspicuity. The abbreviated protocol, con- sisting of a T2-weighted fat-suppressed sequence and a pre- and post-contrast T1- weighted sequence, reached a sensitivity of 97.8 - 99.4%, comparable to previously mentioned studies52,53,76. In addition, in the Heacocks study54, information about
prior imaging and clinical history increased detection rates. T2-weighted imaging increased confidence and lesion conspicuity, however, it did not increase detection rates. Initial enhancement rate was significantly correlated with tumor grade, in- vasive disease, and lesion conspicuity, supporting the idea that rapid wash-in char- acteristics of malignancy may underpin the efficacy of abbreviated MRI sequences. This finding raises the possibility that cancers detected by an abbreviated MRI ex- amination only may be of higher grade, i.e. more biologically active lesions, po- tentially counteracting the drawback of overdiagnosis intrinsically associated with every screening program.
From the studies investigating abbreviated protocols, we can conclude that there is still no clear consensus in which sequences are beneficial and needed for an ab-