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First-Pass CT Perfusion in Small Peripheral Lung Cancers

Posted Jul 31, 2013 Updated Apr 10, 2023
By Fei Shan MD , Wei Xing PhD , Jianguo Qiu PhD , Zhiyong Zhang MD , Shan Yang MD
8 min read

Rationale and Objectives

To evaluate the effect of the temporal interval (TI) between scan acquisitions on the radiation dose and vascular parameters of computed tomography perfusion (CTP) in small peripheral lung cancers.

Materials and Methods

With 7 excluded, 40 patients with peripheral lung cancer (diameter ≤4 cm) prospectively underwent a 30-second CTP study. Vascular parameters were calculated for TI datasets of 0, 1, 1.5, 2, 2.5, and 3.5 seconds. With the TI and tumor diameter as fixed effects, univariate general linear model analysis was used to compare the vascular parameters at interval datasets with the reference CTP of 0 seconds.

Results

The TI had an impact on the blood flow and transit time ( P < .001 for both) but not on the blood volume and permeability surface area. The diameter influenced four vascular parameters ( P < .001 for all). Compared to the reference, no statistical differences were found in the four parameters at intervals of 0.5, 1, and 1.5 seconds ( P > .05 for all). In addition, blood flow was overestimated and transit was underestimated with increasing intervals of 2, 2.5, and 3.5 seconds ( P < .05 for all), but not the remaining parameters. An increased TI of 0.5–1.5 seconds resulted in an estimated radiation dose reduction of 50–73%.

Conclusion

The TI of 1.5 seconds between scan acquisitions in first-pass phase of CTP could be used to optimally balance the radiation dose and quantitative estimation in small peripheral lung cancers.

The assessment of tumoral neovascularization can be approximated by computed tomography perfusion (CTP) , dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) , and DCE ultrasound (DCE-US) . Based on the highly linear and predictable contrast pharmacodynamics of CT , the high temporal resolution of the scan acquisitions, the benefits of wide availability, and the relatively low cost, the significance of CTP had been explored and verified in clinical oncology studies . In the chest, CTP has also been increasingly promoted for use in the differential diagnosis or neovascularization of local pulmonary lesions, especially after the introduction of the volume or whole tumor mode .

When CTP is used, the temporal interval (TI) in the scan protocol should be set to a dedicated level for the accurate estimation of vascular parameters and radiation dose. Several authors evaluated the TI in the CTP use of flow phantom for tumors in sites with less respiratory-motion artifacts, such as the retroperitoneal and pelvic cavities . Recently, Miles et al proposed that the temporal sampling interval should not be less frequent than one image every 2 seconds for the measurement of tumoral blood flow (BF). However, to our knowledge, an appropriate TI in the first-pass phase of CTP in lung cancer, which involves intrinsic respiratory motion, that could be used to estimate the vascular parameters and to substantially reduce the radiation dose has not been studied in a major academic journal. The purpose of our study was to determine this verified TI in a perfusion scan protocol in first-pass CTP used to characterize small peripheral lung cancers.

Materials and methods

Patients

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Dynamic and Routine CT Studies

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CTP Data Processing and Analysis

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Radiation Dose

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Statistical Analysis

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Results

Clinical Features and Histopathologic Results

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Dynamic Image Quality and Vascular Parameters at Sampling TIs

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Table 1

Vascular Parameters of Small Peripheral Lung Cancers at Sampling Temporal Intervals between CTP Acquisitions ( N = 40)

Parameter Temporal Intervals 0 sec 0.5 sec 1 sec 1.5 sec 2 sec 2.5 sec 3.5 sec BF

(mL/min / 100 g) Mean ± SD 71.58 ± 33.01 65.03 ± 32.00 73.83 ± 41.15 72.83 ± 33.53 81.96 ± 36.99 85.56 ± 42.03 89.38 ± 37.29 95% CI 61.02–82.14 54.80–75.26 60.67–86.98 62.11–83. 5 6 70.13–93.79 72.12–99.00 77.46–101.31P NA .337 1.000 1.000.035.026.002 BV

(mL/100 g) Mean ± SD 4.26 ± 1.66 4.40 ± 1.55 4.49 ± 1.72 4.43 ± 1.57 4.38 ± 1.38 4.36 ± 1.59 4.42 ± 1.50 95% CI 3.73–4.79 3.90–4.89 3.94–5.04 3.93–4.93 3.94–4.83 3.86–4.87 3.95–4.90P NA .943 .648 .489 .65 .987 .902 MTT

(sec) Mean ± SD 6.43 ± 2.94 6.57 ± 2.69 6.10 ± 2.29 5.80 ± 2.34 4.92 ± 1.81 4.79 ± 1.69 4.64 ± 1.91 95% CI 5.49–7.37 5.71–7.43 5.37–6.84 5.05–6.55 4.35–5.50 4.25–5.33 4.03–5.25P NA .999 .922 .428.001<.001<.001 PS

(mL/min / 100 g) Mean ± SD 18.22 ± 8.03 17.88 ± 7.27 16.77 ± 9.00 18.10 ± 8.20 16.36 ± 9.30 16.15 ± 7.08 18.34 ± 11.37 95% CI 15.66–20.79 15.55–20.20 13.89–19.64 15.48–20.72 13.39–19.33 13.89–18.42 14.71–21.98P NA 1.000 .863 .985 .315 .906 1.000

NA, not applicable; BF, blood flow; BV, blood volume; MTT, mean transit time; PS, capillary permeability–surface area product; CI, confidence interval.

The statistical analysis used a univariate general linear model with a randomized block design and post-hoc Dunnett analysis (with the temporal interval dataset of 0 second set as the control category).

Figure 1, Graph of the variations of vascular parameters at sampling temporal intervals (TI). Every bar in the graph represents the mean and 95% confidence interval of the ratio of intraindividually normalized parameters at different TIs (the reference TI of 0 second = 100%, and other TIs in relation to the measure at the reference). *The BF values at the TIs of 2, 2.5, and 3.5 seconds were higher and the MTT values were lower than those of the reference ( P < .05 for all). All other values were not significantly different from the reference.

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Difference of Vascular Parameters

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Figure 2, Perfusion maps and vascular parameters at the sampling temporal intervals (TI) in a 79-year-old woman with an adenocarcinoma (stage IV, T1N0M1) in the posterior segment of the right superior lung. When the TI ≤ 1.5 seconds was used, the values of blood flow (BF) and mean transit time (MTT) did not change more. With an increase in the TI (≥2 seconds), the BF value increased (from 42.7 mL/sec/100 g at the 0-second interval to 75.40 mL/sec/100 g at the 3.5-second interval), and the MTT value decreased correspondingly. The blood volume (BV) value did not vary more at the TIs from 0 seconds to 3.5 seconds, and the capillary permeability surface area product (PS) value changed irregularly.

Figure 3, Graph of the time–density curves of the input aorta and tumor (the same patient in Figure 2 ) for six temporal intervals (TIs). Compared with the reference TI of 0 second the time to the peak enhancement of the aorta at the TI of 1 second was not changed or that of TI of 1.5 seconds varied 0.5 second (a, b, and c) . However, this time at the TIs of 2 seconds, 2.5 seconds, and 3.5 seconds was decreased 1 second, 1.5 seconds, and 1.5 seconds, respectively (d, e, and f) . The undersampling peak enhancement of the input aorta might lead to the relatively underestimated MTT parameter of the tumor. Since there had not significant differences in the BV parameter of the tumor at the different sampling TIs, and BF = BV/MTT, the BF value was overestimated at the TIs ≥ 2 seconds.

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Estimated Radiation Dose Reduction

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Discussion

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Academic Radiology, Volume 20, Issue 8
Journals General Radiology
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