Prog Med Phys.  2021 Jun;32(2):50-58. 10.14316/pmp.2021.32.2.50.

Effect of the Number of Projected Images on the Noise Characteristics in Tomosynthesis Imaging

• Fukui R
• Matsuura R
• Kida K
• Goto S

• KMID: 2516964
• DOI: http://doi.org/10.14316/pmp.2021.32.2.50

Abstract

Purpose
In this study, we investigated the relationship between the noise characteristics and the number of projected images in tomosynthesis using a digital phantom.
Methods
The digital phantom consisted of a columnar phantom in the center of the image and a spherical phantom with a diameter of 80 pixels. A virtual scan was performed, and 128 projected images (Tomo_w/o) of the phantoms were obtained. The image noise according to the Poisson distribution was added to the projected images (Tomo_×1). Furthermore, another projected image with additional noise was prepared (Tomo_×1/2). For each dataset, we created datasets with 64 (half) and 32 (quarter) projections by removing the even-numbered images twice from the 128 (fully) projected images. Tomosynthesis images were reconstructed by filtered back projection (FBP). The modulation transfer function (MTF) was estimated using the sphere method, and the noise power spectrum (NPS) was estimated using the two-dimensional Fourier transform method.
Results
The MTFs did not change between datasets, and the NPSs improved as the number of projected images increased. The noise characteristics of the Tomo_×1_half images were the same as those of the Tomo_×1/2_full.
Conclusions
To achieve a reduction in the patient dose in tomosynthesis acquisition, we recommend reducing the number of projected images rather than reducing the dose per projection.

Keyword

Tomosynthesis; Noise power spectrum; Modulation transfer function; Number of projections; Poisson distribution

Figure

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  Fig. 1 Schematic of the digital phantom. The pixel values of the columnar and spherical phantoms are 6,000 and 30,000, respectively.

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  Fig. 2 Schematic of the alignment used for acquiring the projected and tomosynthesis images.

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  Fig. 3 Angular projected images acquired when the simulated X-ray tube was positioned at ±45° and the center.

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  Fig. 4 Tomosynthesis images (a) without image noise (Tomo_w/o), (b) with one-time image noise (Tomo_×1), and (c) with two-time image noise (Tomo_×1/2).

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  Fig. 5 Region of interest (ROI) positions for (a) modulation transfer function (MTF) and (b) noise power spectrum (NPS).

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  Fig. 6 Results of the modulation transfer functions (MTFs) for (a) Tomo_w/o, (b) Tomo_×1, (c) Tomo_×1/2, and (d) different amounts of image noise. proj., projection.

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  Fig. 7 Noise power spectrum (NPS) of the Tomo_w/o datasets in the (a) vertical and (b) horizontal directions. proj., projection.

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  Fig. 8 Noise power spectrum (NPS) of the Tomo_×1 and _×1/2 datasets in the (a) vertical and (b) horizontal directions. proj., projection.

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  Fig. 9 Noise power spectrum (NPS) of the full and half projection of the Tomo_×1 and _×1/2 datasets in the (a) vertical and (b) horizontal directions. proj., projection.

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  Fig. 10 Relationship between the number of projected images and the noise power spectrum (NPS) value at 2.0 cycles/mm.

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  Fig. 11 Samples of (a) the Tomo_×1 half projection and (b) the Tomo_×1/2 full projection.

Reference

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