Biomedical subjects

C Kamphuis

Publications and source records attributed to C Kamphuis.

5 recordsLinked to original sources

PubMed1998

Dual matrix ordered subsets reconstruction for accelerated 3D scatter compensation in single-photon emission tomography.

Three-dimensional (3D) iterative maximum likelihood expectation maximization (ML-EM) algorithms for single-photon emission tomography (SPET) are capable of correcting image-degrading effects of non-uniform attenuation, distance-dependent camera response and patient shape-dependent scatter. However, the resulting improvements in quantitation, resolution and signal-to-noise ratio (SNR) are obtained at the cost of a huge computational burden. This paper presents a new acceleration method for ML-EM: dual matrix ordered subsets (DM-OS). DM-OS combines two acceleration methods: (a) different matrices for projection and back-projection and (b) ordered subsets of projections. DM-OS was compared with ML-EM on simulated data and on physical thorax phantom data, for both 180 degrees and 360 degrees orbits. Contrast, normalized standard deviation and mean squared error were calculated for the digital phantom experiment. DM-OS resulted in similar image quality to ML-EM, even for speed-up factors of 200 compared to ML-EM in the case of 120 projections. The thorax phantom data could be reconstructed 50 times faster (60 projections) using DM-OS with preservation of image quality. ML-EM and DM-OS with scatter compensation showed significant improvement of SNR compared to ML-EM without scatter compensation. Furthermore, inclusion of complex image formation models in the computer code is simplified in the case of DM-OS. It is thus shown that DM-OS is a fast and relatively simple algorithm for 3D iterative scatter compensation, with similar results to conventional ML-EM, for both 180 degrees and 360 degrees acquired data.

Algorithms↗

PubMed1998

Accelerated iterative transmission CT reconstruction using an ordered subsets convex algorithm.

Iterative maximum likelihood (ML) transmission computed tomography algorithms have distinct advantages over Fourier-based reconstruction, but unfortunately require increased computation time. The convex algorithm [1] is a relatively fast iterative ML algorithm but it is nevertheless too slow for many applications. Therefore, an acceleration of this algorithm by using ordered subsets of projections is proposed [ordered subsets convex algorithm (OSC)]. OSC applies the convex algorithm sequentially to subsets of projections. OSC was compared with the convex algorithm using simulated and physical thorax phantom data. Reconstructions were performed for OSC using eight and 16 subsets (eight and four projections/subset, respectively). Global errors, image noise, contrast recovery, and likelihood increase were calculated. Results show that OSC is faster than the convex algorithm, the amount of acceleration being approximately proportional to the number of subsets in OSC, and it causes only a slight increase of noise and global errors in the reconstructions. Images and image profiles of the reconstructions were in good agreement. In conclusion, OSC and the convex algorithm result in similar image quality but OSC is more than an order of magnitude faster.

Algorithms↗

PubMed1998

Half-fanbeam collimators combined with scanning point sources for simultaneous emission-transmission imaging.

UNLABELLED: One type of SPECT system often used for simultaneous emission-transmission tomography is equipped with parallel-hole collimators, moving line sources (MLS) and electronic windows that move in synchrony with the sources. Although downscatter from the emission distribution is reduced by the use of the electronic window, this still can represent a sizable fraction of the transmitted counts. These systems have relatively poor spatial resolution and use costly transmission sources. METHODS: Using a two-head SPECT system, with heads at right angles, two 153Gd line sources (5800 MBq each) were replaced by two 153Gd point sources of only 750 MBq each and positioned to move along the focal lines of two half-fanbeam collimators. A suitable acquisition protocol for a moving point source (MPS) system was selected by considering the results of a simulation study. With this protocol, physical phantom experiments were conducted. RESULTS: Simulations showed that by using two half-fanbeam collimators, a gantry rotation of 90 degrees, such as used for 180 degrees acquisition with parallel-beam collimators for cardiac imaging, was insufficient. A gantry rotation of 180 degrees resulted in attenuation maps where only an area to the posterior of a 400-mm wide thorax phantom was affected by truncation. The MPS system had a 14.7 times higher sensitivity for transmission counts than the MLS system. Despite the smaller sources in the MPS system, the number of acquired transmission counts was a factor 1.91 times higher compared with the MLS system, resulting in reduced noise. The relative downscatter contribution from 99mTc (140 keV) in the 153Gd moving electronic window (100 keV) was reduced by a factor of 1.81. Transmission images of a rod phantom with segments containing acrylic rods of different diameters showed an improvement of resolution in favor of the MPS system from about 11 mm to about 6 mm (five instead of two segments of rods were clearly visible). In addition, the noise level in the MPS thorax transmission images was significantly lower. CONCLUSION: The MPS system has important advantages when compared with the MLS system. The use of low-activity point sources is economically beneficial when compared with line sources and reduces radiation exposure to staff and patients.

Equipment Design↗

PubMed1997

Scatter compensation methods in 3D iterative SPECT reconstruction: a simulation study.

Effects of different scatter compensation methods incorporated in fully 3D iterative reconstruction are investigated. The methods are: (i) the inclusion of an 'ideal scatter estimate' (ISE); (ii) like (i) but with a noiseless scatter estimate (ISE-NF); (iii) incorporation of scatter in the point spread function during iterative reconstruction ('ideal scatter model', ISM); (iv) no scatter compensation (NSC); (v) ideal scatter rejection (ISR), as can be approximated by using a camera with a perfect energy resolution. The iterative method used was an ordered subset expectation maximization (OS-EM) algorithm. A cylinder containing small cold spheres was used to calculate contrast-to-noise curves. For a brain study, global errors between reconstruction and 'true' distributions were calculated. Results show that ISR is superior to all other methods. In all cases considered, ISM is superior to ISE and performs approximately as well as (brain study) or better than (cylinder data) ISE-NF. Both ISM and ISE improve contrast-to-noise curves and reduce global errors, compared with NSC. In the case of ISE, blurring of the scatter estimate with a Gaussian kernel results in slightly reduced errors in brain studies, especially at low count levels. The optimal Gaussian kernel size is strongly dependent on the noise level.

Algorithms↗

PubMed1994

Differential blockade of the renal vasoconstrictor and diuretic responses to endothelin-1 by endothelin antagonist.

1. The effect of cyclo(D-Trp-D-Asp-Pro-D-Val-Leu) (or BQ123), a selective ETA receptor antagonist, on the vasoconstrictor and diuretic responses elicited by endothelin-1 (ET-1) was examined in conscious sheep with chronic indwelling renal arterial cannulae. 2. Using low dose close renal arterial infusion, ET-1 has potent effects on the kidney causing a marked decrease in effective renal plasma flow and an increase in urine output and free water clearance in the normally hydrated animal. 3. The vasoconstrictor response to renal arterial infusion of ET-1 at 5 micrograms/h was blunted by renal arterial infusion of the ETA receptor selective antagonist, BQ123 (400 micrograms/h). 4. In contrast, the effect of ET-1 on urine production and free water clearance was not affected by this dose of BQ123. 5. The differential effect of BQ123 on renal blood flow and urine production suggests that these effects of endothelin on the kidney are mediated through different receptor mechanisms.

Amino Acid Sequence↗