Khawaja Ranish Deedar Ali, Singh Sarabjeet, Lira Diego, Bippus Rolf, Do Synho, Padole Atul, Pourjabbar Sarvenaz, Koehler Thomas, Shepard Jo-Anne, Kalra Mannudeep K
From the *MGH Imaging, Division of Thoracic Radiology, Massachusetts General Hospital and Harvard Medical School, Boston, MA; and †Philips Technologie GmbH, Innovative Technologies, Hamburg, Germany.
J Comput Assist Tomogr. 2014 Sep-Oct;38(5):760-7. doi: 10.1097/RCT.0000000000000098.
The purpose of this study was to assess pulmonary lesion detection, diagnostic confidence, and noise reduction in sparse-sampled (SpS) computed tomographic (CT) data of submillisievert (SubmSv) chest CT reconstructed with iterative reconstruction technique (IRT).
This Human Insurance Portability and Accountability-compliant, institutional review board-approved prospective study was performed using SpS-SubmSv IRT chest CT in 10 non-obese patients (body-mass index, 21-35 kg/m; age range, 26-90 years). Written informed consent was obtained. The patients were scanned at standard-dose CT (mean [SD] volumetric CT dose index, 6 [0.9] mGy; mean [SD] dose-length product, 208 ± 44 mGy·cm; and mean [SD] effective dose, 3 [0.6] mSv) and at SubmSv dose (1.8 [0.2] mGy, 67 [2] mGy·cm, 0.9 [0.03] mSv, respectively) on a Philips 128-slice CT scanner with double z-sampling. Sparse angular sampling data were reconstructed using 25% of the angular projections from the SubmSv sinogram to reduce the number of views and radiation dose by approximately 4-fold. Hence, the patients were scanned and then, simulation-based sparse sampling was performed with a resultant dose hypothetical SpS scan estimated mathematically (0.2 mSv). From each patient data, 3 digital imaging and communications in medicine series were generated: SpS-SubmSv with IRT, fully sampled SubmSv filtered back projection (FBP), and fully sampled standard-dose FBP (SD-FBP). Two radiologists independently assessed these image series for detection of lung lesions, visibility of small structures, and diagnostic acceptability. Objective noise was measured in the thoracic aorta, and noise spectral density was obtained for SpS-SubmSv IRT, SubmSv-FBP, and SD-FBP.
The SpS-SubmSv IRT resulted in 75% (0.2/0.9 mSv) and 92% (0.2/2.9 mSv) dose reduction, when compared with the fully sampled SubmSv-FBP and SD-FBP, respectively. Images of SpS-SubmSv displayed all 46 lesions (most <1 cm, 30 lung nodules, 7 ground glass opacities, 9 emphysema) seen on the SubmSv-FBP and SD-FBP data sets. Lesion margins with sparse-sampled data were deemed acceptable compared with both SubmSv-FBP and SD-FBP. Overall diagnostic confidence was maintained with SpS-SubmSv IRT despite the presence of minor pixilation artifacts in 3 of 10 cases. The SpS-SubmSv IRT showed 63% and 38% noise reduction when compared with SubmSv-FBP (P < 0.0001) and SD-FBP (P < 0.01), respectively, with no significant change in Hounsfield unit values (P > 0.05). Noise-spectral density showed that SpS-SubmSv IRT gives a linear decrease over frequency in the semilog plot and an exponential decrease of noise power over frequency compared with SubmSv-FBP and SD-FBP.
More than 90% dose reduction could be achieved with one-fourth sparse-sampled and SubmSv chest CT examination when reconstructed with IRT. Chest CT dose at one fourth of a millisievert with SpS is possible with optimal lesion detection and diagnostic confidence for the evaluation of pulmonary findings.
本研究旨在评估采用迭代重建技术（IRT）重建的亚毫西弗（SubmSv）胸部CT稀疏采样（SpS）数据中的肺部病变检测、诊断置信度和降噪效果。
本前瞻性研究符合《健康保险流通与责任法案》要求，经机构审查委员会批准，对10名非肥胖患者（体重指数，21 - 35 kg/m²；年龄范围，26 - 90岁）进行SpS-SubmSv IRT胸部CT检查。获得了书面知情同意书。患者在飞利浦128层CT扫描仪上进行标准剂量CT扫描（平均[标准差]容积CT剂量指数，6 [0.9] mGy；平均[标准差]剂量长度乘积，208 ± 44 mGy·cm；平均[标准差]有效剂量，3 [0.6] mSv）和SubmSv剂量扫描（分别为1.8 [0.2] mGy、67 [2] mGy·cm、0.9 [0.03] mSv），采用双z采样。使用来自SubmSv正弦图25%的角度投影重建稀疏角度采样数据，以将视图数量和辐射剂量减少约4倍。因此，对患者进行扫描，然后通过数学方法估算假设的SpS扫描的剂量进行基于模拟的稀疏采样（0.2 mSv）。从每个患者的数据中生成3个医学数字成像和通信系列：SpS-SubmSv与IRT、全采样SubmSv滤波反投影（FBP）以及全采样标准剂量FBP（SD-FBP）。两名放射科医生独立评估这些图像系列，以检测肺部病变、小结构的可见性和诊断可接受性。在胸主动脉中测量客观噪声，并获得SpS-SubmSv IRT、SubmSv-FBP和SD-FBP的噪声谱密度。
与全采样SubmSv-FBP和SD-FBP相比，SpS-SubmSv IRT分别使剂量降低了75%（0.2/0.9 mSv）和92%（0.2/2.9 mSv）。SpS-SubmSv的图像显示了在SubmSv-FBP和SD-FBP数据集中看到的所有46个病变（大多数<1 cm，30个肺结节，7个磨玻璃影，9个肺气肿）。与SubmSv-FBP和SD-FBP相比，稀疏采样数据的病变边缘被认为是可接受的。尽管10例中有3例存在轻微像素化伪影，但SpS-SubmSv IRT仍保持了总体诊断置信度。与SubmSv-FBP（P < 0.0001）和SD-FBP（P < 0.01）相比，SpS-SubmSv IRT分别显示出63%和38%的降噪效果，亨氏单位值无显著变化（P > 0.05）。噪声谱密度表明，与SubmSv-FBP和SD-FBP相比，SpS-SubmSv IRT在半对数图中随频率呈线性下降，噪声功率随频率呈指数下降。
采用IRT重建时，四分之一稀疏采样的SubmSv胸部CT检查可实现超过90%的剂量降低。对于肺部检查结果的评估，以四分之一毫西弗的剂量进行SpS胸部CT检查，能够实现最佳的病变检测和诊断置信度。
