Detection of prostate cancer bone metastases with fast whole-body 99mTc-HMDP SPECT/CT using a general-purpose CZT system

Abstract

Background: We evaluated the effects of acquisition time, energy window width, and matrix size on the image quality, quantitation, and diagnostic performance of whole-body ^99mTc-HMDP SPECT/CT in the primary metastasis staging of prostate cancer.

Methods: Thirty prostate cancer patients underwent ^99mTc-HMDP SPECT/CT from the top of the head to the mid-thigh using a Discovery NM/CT 670 CZT system with list-mode acquisition, 50-min acquisition time, 15% energy window width, and 128 × 128 matrix size. The acquired list-mode data were resampled to produce data sets with shorter acquisition times of 41, 38, 32, 26, 20, and 16 min, narrower energy windows of 10, 8, 6, and 4%, and a larger matrix size of 256 × 256. Images were qualitatively evaluated by three experienced nuclear medicine physicians and quantitatively evaluated by noise, lesion contrast and SUV measurements. Diagnostic performance was evaluated from the readings of two experienced nuclear medicine physicians in terms of patient-, region-, and lesion-level sensitivity and specificity.

Results: The originally acquired images had the best qualitative image quality and lowest noise. However, the acquisition time could be reduced to 38 min, the energy window narrowed to 8%, and the matrix size increased to 256 × 256 with still acceptable qualitative image quality. Lesion contrast and SUVs were not affected by changes in acquisition parameters. Acquisition time reduction had no effect on the diagnostic performance, as sensitivity, specificity, accuracy, and area under the receiver-operating characteristic curve were not significantly different between the 50-min and reduced acquisition time images. The average patient-level sensitivities of the two readers were 88, 92, 100, and 96% for the 50-, 32-, 26-, and 16-min images, respectively, and the corresponding specificities were 78, 84, 84, and 78%. The average region-level sensitivities of the two readers were 55, 58, 59, and 56% for the 50-, 32-, 26-, and 16-min images, respectively, and the corresponding specificities were 95, 98, 96, and 95%. The number of equivocal lesions tended to increase as the acquisition time decreased.

Conclusion: Whole-body ^99mTc-HMDP SPECT/CT can be acquired using a general-purpose CZT system in less than 20 min without any loss in diagnostic performance in metastasis staging of high-risk prostate cancer patients.

Keywords: Bone; CZT; SPECT/CT; Time reduction; Whole-body.

Fig. 1

Whole-body ^99mTc-HMDP SPECT maximum intensity projections of an 80-year-old prostate cancer patient with different acquisition times. The images are filtered using a Gaussian filter with 7-mm FWHM

Fig. 2

Whole-body ^99mTc-HMDP SPECT maximum intensity projections of a 72-year-old prostate cancer patient with different acquisition times and post-processing filters. The 50-, 32-, and 26-min images are filtered using Gaussian filters with FWHMs of 7, 10, and 12 mm, respectively, and the 16-min image is filtered using a Butterworth filter with a cutoff frequency of 0.48 cycles/cm and an order of 1.2. The 16-min image is acquired and processed using the same parameters as in an earlier study [11]