Fürst S, Souvatzoglou M, Martinez-Möller A, Schwaiger M, Nekolla S G, Ziegler S I
Sebastian Fürst, Dipl.-Phys., Department of Nuclear Medicine, Technische Universität München, Ismaninger Str. 22, 81675 München, Germany Tel. +49/(0)89/41 40 45 72, Fax +49/(0)89/41 40 49 38, E-mail:
Nuklearmedizin. 2014;53(3):79-87. doi: 10.3413/Nukmed-0608-13-07. Epub 2014 Mar 21.
The surface coils of the Biograph mMR integrated PET/MR system were optimised for PET, but are otherwise unaccounted for. The patient table is still more massive than those of PET/CT devices. The goal was to assess those hardware effects on quantification, count statistics, image quality and scan time both with phantoms and in patients and to investigate their clinical relevance.
PATIENTS, MATERIAL, METHODS: PET phantom data were acquired with and without the patient table. Image noise was expressed as relative standard deviation and compared to a state-of-the-art PET/CT scanner. Protocols of the phantom/patient study regarding the surface coils were similar. Thoraces/abdomens of 11 patients were scanned with and without a coil (1 BP, 4 min). Mean uptake and standard deviation in a cubical VOI were derived and expressed as SUV.
The patient table reduced the number of true coincidences (trues) by 19% (PET/MR) and by 11% (PET/CT). The scan duration for the mMR had to be increased by approximately 30% to achieve a noise level comparable to that of the PET/CT. Decreased SUVs with coil observed in the phantom were confirmed by the patient study. By removing the coil, the mean liver SUV increased by (6 ± 2)%. With (+3 ± 14)%, the average change was similar in lesions, but exceeded 20% in almost one fifth of them. The number of trues grew by (6 ± 1)% for the patients and by 7% for the phantom.
Due to the additional attenuation caused by MR hardware, PET scan durations would have to be increased compared to current PET/CTs to provide similar image noise levels. The effect of the coils is mostly in the order of statistical fluctuations. In tumour lesions, it is more pronounced and shows a larger variability. Therefore, coils should be included in the attenuation correction to ensure accurate quantification and thus comparability across PET/MR and PET/CT scanners and within patient populations.
Biograph mMR一体化PET/MR系统的表面线圈是针对PET进行优化的，但其他方面未作考虑。其检查床仍比PET/CT设备的检查床更重。目的是通过体模和患者研究评估这些硬件因素对定量分析、计数统计、图像质量和扫描时间的影响，并研究其临床相关性。
患者、材料、方法：使用和不使用检查床采集PET体模数据。图像噪声以相对标准差表示，并与一台先进的PET/CT扫描仪进行比较。体模/患者研究中关于表面线圈的方案相似。对11例患者的胸部/腹部进行了带线圈和不带线圈的扫描（1次呼吸门控，4分钟）。在一个立方体感兴趣区内得出平均摄取量和标准差，并表示为标准化摄取值（SUV）。
检查床使真符合事件（真符合）数量减少了19%（PET/MR）和11%（PET/CT）。mMR的扫描持续时间必须增加约30%才能达到与PET/CT相当的噪声水平。体模研究中观察到的带线圈时SUV降低的情况在患者研究中得到了证实。去除线圈后，肝脏平均SUV增加了（6±2）%。病变的平均变化为（+3±14）%，虽与之相似，但近五分之一的病变超过了20%。患者的真符合事件数量增加了（6±1）%，体模增加了7%。
由于MR硬件造成的额外衰减，与当前的PET/CT相比，PET扫描持续时间必须增加才能提供相似的图像噪声水平。线圈的影响大多在统计波动范围内。在肿瘤病变中，这种影响更为明显且变异性更大。因此，应将线圈纳入衰减校正，以确保准确的定量分析，从而保证PET/MR和PET/CT扫描仪之间以及患者群体内部的可比性。
