Multiple studies show that abbreviated contrast-enhanced MRI protocols are suitable for breast cancer screening and superior to current methods.
Christiane K. Kuhl, University of Aachen, Aachen, Germany, believes that breast cancer screening is at a turning point. “It is MRI that detects the biologically important cancer, not mammography,” she said. Mammography or DBT detect morphologic changes and calcifications.
However, rapidly growing cancers do not necessarily show fibrosis or calcifications. Moreover, mammography has a low sensitivity compared to other modalities. More than a third of all cancers are interval cancers, i.e. they have not been detected by mammography and developed in between screening rounds. “Those have a significantly worse prognosis than those cancers detected by mammography,” Kuhl stated.
Another issue is dense breast tissue: it may mask the cancer and not be detected by mammography.
Digital breast tomosynthesis (DBT) and ultrasound have been proposed as (additional) screening modalities. However, as Kuhl demonstrated the results of various studies, the additional cancer yield by adding DBT to mammography varies between 1.1 and 2.7 cases per 1000. Using additional ultrasound increases cancer yield between 1.7 to 4.6 cases per 1000.
In contrast, only screening by MRI yields in a mean of 14.6 additionally detected cancers per 1000. Kuhl’s own study, published in 2017, showed an improved detection of breast cancer and prognostically relevant breast cancer in women with average risk of developing breast cancer at a rate of 15.5 per 1000 (Kuhl C et al. 2017). Additionally, the interval cancer rate was nil. Kuhl therefore promoted MRI as a single screening tool.
Long examination and interpretation times as well as high costs are hurdles towards MRI being used as a screening tool. Kuhl developed an abbreviated MRI protocol which takes only three minutes instead of 15. She showed images of breast MRI examinations that proved that the first (one-minute) post-contrast subtracted image (FAST) delivers the better lesion enhancement compared to later captured images.
These are processed to maximum intensity projection images (MIP) that are used to detect and characterize significant lesion enhancement. Kuhl showed several examples. “The reading time for MIP images is approximately 2.8 seconds,” she said. It takes ten times more to read individual subtracted images, and even much longer – up to 20 minutes – to read mammography or ultrasound images. Moreover, the abbreviated MRI protocol is not inferior to the full MRI protocol.
At Kuhl’s institution, breast MRI examinations are performed at 1.5 T with axial bilateral imaging, no fat saturation and a 2D multi-slice gradient echo (GRE). “We found that breast immobilization by fixation in slice encoding direction ensures good image quality,” Kuhl said.
Kuhl provided evidence from multiple studies that show the superiority of MRI for breast cancer detection to mammography, DBT and ultrasound. She developed an abbreviated MRI protocol that would make MRI suitable for screening. “We need robust, simple and conservative acquisition protocols to ensure reproducible image quality and avoid false-positive results,” she said.
Presentation Title: Abbreviated Breast MRI: A Game Changer for Screening of Breast Cancer
Speaker: Christiane K. Kuhl, University of Aachen, Aachen, Germany
Date: 2017-11-30
Session code: SPSH50A
多项研究表明，简化对比增强MRI方案适用于乳腺癌筛查，且优于当前临床检查。
德国亚琛大学的Christiane K. Kuhl认为乳腺癌筛查正处于转折点。“MRI能够检测生物学重要癌症，而非乳房X线照相术，”她说。乳房X线照相术或DBT仅可检测乳腺形态变化和钙化。
然而，快速生长的癌症并不一定表现为纤维化或钙化。此外，与其他检查相比，乳房X线照相术的灵敏度较低。超过三分之一的癌症是期間癌症，即乳房X线照相术未检出，但两次筛查期间发生的癌症。Kuhl说：“期間癌症的预后显著劣于乳房X线照相术检出癌症。”
另一个问题是致密性乳房组织：致密性乳房组织可能掩盖癌症，使得乳房X线照相术无法检出。
数字乳腺断层合成X线成像（DBT）和超声已被提议作为（额外）筛查方式。然而， Kuhl基于各类研究结果得出：乳房X线照相术联合DBT情况下，额外癌症检出率为1.1和2.7/1000例。联用超声检查情况下，额外癌症检出率可增加至1.7-4.6/1000例。
相比之下， MRI单项检查的平均额外癌症检出率为14.6/ 1000例。2017年，Kuhl发表了自己开展的一项研究结果，表明MRI可提高平均乳腺癌风险女性的乳腺癌和预后相关乳腺癌检出率（15.5 / 1000例）（Kuhl C等人，2017年）。此外，期間癌症率为零。因此，Kuhl认为MRI应作为乳腺癌的单一筛查工具。
检查和读片时间过长以及价格昂贵使得MRI无法作为筛查工具使用。Kuhl开发了一种简化MRI方案，操作时间仅为3分钟，远远短于15分钟的常规操作。她通过乳腺MRI检查的图像证实首次（1分钟）对比后减影图像（FAST）的病灶强化效果优于后期采集图像。
检查过程中，应将图像处理为最大强度投影图像（MIP），以检测和描述显著病灶强化特征。Kuhl展示了数个示例。“MIP图像的读片时间约为2.8秒，”她说。读片单个减影图像需要十倍以上的时间，读片乳房X线照相术或超声图像甚至长达20分钟的时间方可完成。此外，简化MRI方案并不逊于完整MRI方案。
在Kuhl的工作单位，乳腺MRI检查为1.5 T轴向双侧成像，而不使用脂肪饱和度和2D多层面梯度回波（GRE）序列。“我们发现通过方向编码层面固定实现乳房固定能够保证图像的高质量，”Kuhl说。
Kuhl通过多项研究证据表明MRI的乳腺癌检测效果优于乳房X线照相术、DBT和超声。她开发了一个简化MRI方案，使MRI适用于筛查。她说：“我们需要稳健、简单和保守的采集方案，以确保图像质量的重现性，避免假阳性结果。”
演讲题目：简化乳腺MRI方案：乳腺癌筛查方式的有效替代方案
演讲者：Christiane K. Kuhl，德国亚琛大学
日期：2017年11月30日
会议代码：SPSH50A
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