Conjugate Views Research Articles

Dedicated cone-beam breast CT using laterally-shifted detector geometry: Quantitative analysis of feasibility for clinical translation.

High-resolution, low-noise detectors with minimal dead-space at chest-wall could improve posterior coverage and microcalcification visibility in the dedicated cone-beam breast CT (CBBCT). However, the smaller field-of-view necessitates laterally-shifted detector geometry to enable optimizing the air-gap for x-ray scatter rejection. To evaluate laterally-shifted detector geometry for CBBCT with clinical projection datasets that provide for anatomical structures and lesions. CBBCT projection datasets (n = 17 breasts) acquired with a 40×30 cm detector (1024×768-pixels, 0.388-mm pixels) were truncated along the fan-angle to emulate 20.3×30 cm, 22.2×30 cm and 24.1×30 cm detector formats and correspond to 20, 120, 220 pixels overlap in conjugate views, respectively. Feldkamp-Davis-Kress (FDK) algorithm with 3 different weighting schemes were used for reconstruction. Visual analysis for artifacts and quantitative analysis of root-mean-squared-error (RMSE), absolute difference between truncated and 40×30 cm reconstructions (Diff), and its power spectrum (PSDiff) were performed. Artifacts were observed for 20.3×30 cm, but not for other formats. The 24.1×30 cm provided the best quantitative results with RMSE and Diff (both in units of μ, cm-1) of 4.39×10-3±1.98×10-3 and 4.95×10-4±1.34×10-4, respectively. The PSDiff (>0.3 cycles/mm) was in the order of 10-14μ2mm3 and was spatial-frequency independent. Laterally-shifted detector CBBCT with at least 220 pixels overlap in conjugate views (24.1×30 cm detector format) provides quantitatively accurate and artifact-free image reconstruction.

This Month in Pediatric Urology

No AccessJournal of UrologyThis Month in Pediatric Urology1 Feb 2016This Month in Pediatric Urology Julian S. Wan Julian S. WanJulian S. Wan More articles by this author View All Author Informationhttps://doi.org/10.1016/j.juro.2015.10.168AboutFull TextPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookLinked InTwitterEmail "This Month in Pediatric Urology." The Journal of Urology, 195(2), p. 239 References 1 : The Clavien-Dindo classification of surgical complications is not a statistically reliable system for grading morbidity in pediatric urology. J Urol2016; 195: 460. Link, Google Scholar 2 : Sexual function, social integration and paternity of males with classic bladder exstrophy following urinary diversion. J Urol2016; 195: 465. Link, Google Scholar 3 : Measurement of differential renal function by scintigraphy in hydronephrotic kidneys: importance of conjugate views for accurate evaluation. J Urol2016; 195: 471. Link, Google Scholar © 2016 by American Urological Association Education and Research, Inc.FiguresReferencesRelatedDetails Volume 195Issue 2February 2016Page: 239 Advertisement Copyright & Permissions© 2016 by American Urological Association Education and Research, Inc.MetricsAuthor Information Julian S. Wan More articles by this author Expand All Advertisement PDF downloadLoading ...

Measurement of Differential Renal Function by Scintigraphy in Hydronephrotic Kidneys: Importance of Conjugate Views for Accurate Evaluation

Traditionally a single posterior view is used to measure differential renal function during nuclear renal scintigraphy. Nevertheless, experimental data show important variation in this measurement in the setting of significant hydronephrosis. To date, the impact of degree of hydronephrosis on the accuracy of differential renal function determination has not been addressed. We evaluated the discrepancy between function measured by anterior and posterior views, and the relationship to varying degrees of hydronephrosis. We retrospectively reviewed consecutive mercaptoacetyltriglycine renal scans from 2009 to 2011. Ultrasounds were reviewed and degree of hydronephrosis was recorded using anteroposterior pelvic diameter. Absolute percent difference in differential renal function between each view (anterior minus posterior) was calculated and correlated to anteroposterior pelvic diameter. Patients were stratified into 4 groups according to anteroposterior pelvic diameter, ie less than 10 mm, greater than 10 mm, greater than 15 mm and greater than 25 mm. A total of 519 scans with corresponding ultrasounds were analyzed. Median patient age was 2.26 years. Kidneys with a larger anteroposterior pelvic diameter had a greater discrepancy in function on anterior and posterior views. There was a meaningful discrepancy for anteroposterior pelvic diameter greater than 10 mm (p = 0.034) and greater than 25 mm (p = 0.032). Several statistical models were used to identify a meaningful cut point of 15 mm, where the discrepancy in anterior and posterior views became significant (p = 0.001). The use of single views during nuclear renography for grossly hydronephrotic kidneys is often inaccurate. The discrepancy in differential renal function obtained on the anterior and posterior views is adversely impacted especially as anteroposterior pelvic diameter increases beyond 15 mm. Therefore, we suggest incorporation of conjugate views for estimating differential renal function in patients with hydronephrosis.

Reconstruction of the Attenuated Radon Transform in π-Scheme Short-Scan Spect

In this work, the image reconstruction in π-scheme short-scan single-photon emission computed tomography (SPECT) with nonuniform attenuation is derived in its most general form when π-scheme short-scan SPECT entails data acquisition over disjoint angular intervals without conjugate views totaling to π radians. The reconstruction results are based on decomposition of Novikov's inversion operator into three parts bounded in the L2 sense. The first part involves the measured partial data; the second part is a skew-symmetric operator; the third part is a symmetric and compact contribution. It is showed firstly that the operators involved belong to ℒ(L2(▪)). Furthermore numerical simulations are conducted to demonstrate the effectiveness of the developed method.

Exact emission SPECT reconstruction with truncated transmission data

It is common, even with new SPECT/CT systems, that the transmission data are truncated. This paper develops a method that obtains exact attenuation correction with truncated transmission data. The emission object (e.g., the heart) is assumed to have a finite, convex support, whose emission projections are not truncated. The transmission measurements over the support are available, but may be truncated outside the support (within the torso). A novel emission data reconstruction technique combines emission projections from conjugate views; a modified version of the ML-EM algorithm is used to reconstruct emission data. The attenuation map outside the support is not needed during reconstruction. The transmission measurements through the support are used to pre-scale the emission data and to reconstruct the attenuation map within the support. The attenuation map reconstruction within the support is an interior problem in which only a biased solution can be obtained using an iterative algorithm. The bias is then corrected by identifying a soft tissue region within the support and the known attenuation coefficient values of these pixels for the soft tissue. Proof of convergence of the new algorithm is provided. Computer simulations verify the accuracy of the new method. Conclusions: an exact attenuation map within the support can be obtained provided the attenuation coefficient is known at 1 pixel within the support. The method, which requires emission data over 360°, provides a means to perform attenuation correction in SPECT with truncated transmission data.

The Importance of Obtaining Conjugate Views on Renographic Evaluation of Large Hydronephrotic Kidneys: An In Vitro and Ex Vivo Analysis

It is postulated that significant obstruction leads to decreased ipsilateral renal function. However, maintained or even increased differential renal function is often seen in patients with large hydronephrotic kidneys. The reason for such a phenomenon is unclear. We designed an in vitro and ex vivo experimental model that permits the controlled orientation of thinned renal parenchyma and background activity during gamma camera detection. A 5-step experimental study was designed with balloons or reservoirs containing known amounts of radioisotope. A balloon was incrementally compressed between 2 Plexiglas sheets (step 1). Simultaneous measurement of radio emission was done of 5 glass beakers of varying diameters filled with the same amount of water and (99m)Tc (step 2). A single beaker containing diluted (99m)Tc was interfaced with air (step 3) or water (step 4) at different distances from the gamma camera. Pig kidneys previously injected with dimercapto-succinic acid were removed and scanned (step 5). One of the kidneys was then progressively sliced, thinning its parenchyma, and sliced and nonsliced kidneys were simultaneously scanned again. Progressively increased counts were detected as the projected surface area of the radioactive balloons (step 1) and beakers (step 2) increased. Counts detected were inversely proportional to the amount of water interfaced between the container and the gamma camera. Significantly more radiation was detectable in sliced kidneys containing dimercapto-succinic acid than in intact control kidneys. These findings suggest that the artifactual supranormal differential renal function that is observed during renographic evaluation of large hydronephrotic kidneys actually exists. Parenchymal proximity and distribution in relation to the pelvis are critical determinants. These findings suggest that the conjugate view technique may be more suitable for renographic evaluation of large hydronephrotic kidneys.

Clinical performance and radiation dosimetry of no-carrier-added vs carrier-added 123I-metaiodobenzylguanidine (MIBG) for the assessment of cardiac sympathetic nerve activity.

PurposeWe hypothesized that assessment of myocardial sympathetic activity with no-carrier-added (nca) 123I-meta-iodobenzylguanidine (MIBG) compared to carrier-added (ca) 123I-MIBG would lead to an improvement of clinical performance without major differences in radiation dosimetry.MethodsIn nine healthy volunteers, 15 min and 4 h planar thoracic scintigrams and conjugate whole-body scans were performed up to 48 h following intravenous injection of 185 MBq 123I-MIBG. The subjects were given both nca and ca 123I-MIBG. Early heart/mediastinal ratios (H/M), late H/M ratios and myocardial washout were calculated. The fraction of administered activity in ten source organs was quantified from the attenuation-corrected geometric mean counts in conjugate views. Radiation-absorbed doses were estimated with OLINDA/EXM software.ResultsBoth early and late H/M were higher for nca 123I-MIBG (ca 123I-MIBG early H/M 2.46 ± 0.15 vs nca 123I-MIBG 2.84 ± 0.15, p = 0.001 and ca 123I-MIBG late H/M 2.69 ± 0.14 vs nca 123I-MIBG 3.34 ± 0.18, p = 0.002). Myocardial washout showed a longer retention time for nca 123I-MIBG (p < 0.001). The effective dose equivalent (adult male model) for nca 123I-MIBG was similar to that for ca 123I-MIBG (0.025 ± 0.002 mSv/MBq vs 0.026 ± 0.002 mSv/MBq, p = 0.055, respectively).ConclusionNo-carrier-added 123I-MIBG yields a higher relative myocardial uptake and is associated with a higher myocardial retention. This difference between nca 123I-MIBG and ca 123I-MIBG in myocardial uptake did not result in major differences in estimated absorbed doses. Therefore, nca 123I-MIBG is to be preferred over ca 123I-MIBG for the assessment of cardiac sympathetic activity.

Image reconstruction with a half-detector in single-photon emission computed tomography with nonuniform attenuation

In parallel beam computed tomography, measured projections at conjugate views are mathematically identical. This symmetry can be exploited for either reducing the scanning angle or the size of the detector arrays. In single-photon emission computed tomography (SPECT), because the gamma rays in the conjugate views suffer different photon attenuation, measured projections at conjugate views are generally different. Therefore, it had been widely considered that projections covering 360 deg and the whole detector face are required for exact reconstruction of the distributions of gamma-ray emitters. In this work, we show that projections covering 360 deg, but acquired with a half-detector viewing half of the image space, provide the necessary information to reconstruct a unique image in SPECT with nonuniform attenuation.

π-scheme short-scan SPECT and image reconstruction with nonuniform attenuation.

Because the effects of physical factors such as photon attenuation and spatial resolution are distance-dependent in single-photon emission computed tomography (SPECT), it is generally considered that accurate image reconstruction requires knowledge of the data function over 2/spl pi/. In SPECT with only uniform attenuation, Noo and Wagner (2001) recently showed that an accurate image can be reconstructed from knowledge of the data function over the interval [0, /spl pi/]. In this work, we consider image reconstruction in /spl pi/-scheme SPECT with nonuniform attenuation. In its most general form, /spl pi/-scheme SPECT entails data acquisition over disjoint angular intervals without conjugate views, totaling to /spl pi/ radians. We develop an heuristic perspective for observing that the data function in full-scan SPECT contains redundant information and that the data function in /spl pi/-scheme SPECT contains complete information necessary for accurate image reconstruction. We conduct simulation studies in which the expectation maximization algorithm is used for image reconstruction from the data acquired in /spl pi/-scheme SPECT with nonuniform attenuation. The results in these simulation studies seem to corroborate hypothesis that accurate images can be reconstructed from /spl pi/-scheme data. /spl pi/-scheme SPECT allows data acquisition over different combinations of disjoint angular intervals, thereby providing a flexibility in choosing projection views at which the emitted gamma-rays may undergo the least attenuation and blurring. It should be stressed, however, that the proposed perspective on redundant information is intended only to heuristically reveal the data redundancy in SPECT with nonuniform attenuation and that it has not been demonstrated mathematically to guarantee the stability and exactness of image reconstruction from the /spl pi/-scheme data.

Investigation of large field-of-view transmission imaging for SPECT attenuation compensation with Gd-153, Tc-99m and Ce-139 sources

A recently developed, large field-of-view (FOV), dual head SPECT system was investigated for fast sequential fan-beam (FB) transmission computed tomography (TCT) with various transmission sources. For TCT, the system utilizes a fixed line source at the 77 cm focal line of asymmetric FB collimator. The TCT maps are used for non-uniform attenuation compensation (NUAC) of Tc-99m myocardial SPECT. The heads each have three degrees of freedom (transaxial tilt, radial linear and transaxial linear travel). When the heads are tilted and height adjusted to accommodate different size FOVs (34-53 cm diameter), the symmetric FB geometry only samples part of the FOV. Thus, with full 360 degree acquisitions, the pseudo-asymmetric FB TCT detector utilizes measured conjugate views to avoid truncation artifacts without sacrificing spatial resolution, and minimizes emission contamination compared with other TCT geometries. Transmission line source energies of 100 to 166 keV (from Gd-153, Tc-99m, and Ce-139 line sources) were utilized with rod and sphere, and anthropsmorphic phantoms. The TCT images were reconstructed with iterative ordered subsets estimation maximization (OSEM). Comparisons were made between the emission reconstructions utilizing filtered backprojection (without and with iterative and multiplicative Chang NUAC) and OSEM (without and with NUAC). Based on a derived noise equivalent count rate determination of the three sources, the highest energy yet weakest intensity TCT source outperforms the other sources in the primary myocardial region of interest by approximately a factor of two. The emission contamination for the highest energy transmission source was an order of magnitude smaller than for the other sources with this acquisition geometry. These line sources each demonstrate the potential for suitably compensated images and quantitative myocardial activity profiles with this geometry. Higher energy transmission sources in particular result in more physically accurate attenuation maps useful for SPECT quantitation.

Transmission imaging of large attenuators using a slant hole collimator on a three‐headed SPECT system

By combining conjugate views, truncation-free attenuation profiles of patients can be obtained by using slant hole collimators on three-headed SPECT systems. The alterations in reconstruction algorithms necessary for use with slant hole collimators and potential image artifacts are discussed. Based on an evaluation of the size of objects that can be imaged without truncation and the size of the overlap region in the conjugate views, a 15 degrees slant angle was determined to be optimal. Studies with a 30 degrees slant hole collimator verified the ability of slant hole transmission imaging to provide accurate, truncation-free attenuation maps of a 56 cm lateral width phantom. The center of rotation was determined to be dependent on the slant angle and radius of rotation of the slant collimator. These studies also demonstrated that the spatial resolution in the transaxial plane of the attenuation maps depends on radius of rotation of the slant hole collimator, but does not depend on the radius of rotation of an uncollimated transmission source. A multiline transmission source was investigated for use with estimating the attenuation map in Tc-99m labeled sestamibi perfusion imaging.

Double-Tracer Dosimetry of Organs in Assessment of Bone Marrow Involvement by Two Monoclonal Antibodies

Five patients with ductal breast cancer were studied using simultaneous administration of 99Tcm-labelled BW250/183 and 131I-labelled B72.3 monoclonal antibodies (MAbs). The distribution and dosimetry of these tracers were evaluated using the information from simultaneous anterior and posterior whole body scintigrams, together with 99Tcm and 131I standard activity sources, recorded on an average of 1, 4, 24, 90 and 224 h after injection. A method to eliminate 131I Scatter on 99Tcm-channel was developed. The geometric means of conjugate views and region-of-interest analysis were used to determine organ uptakes, mean residence times and absorbed radiation dose estimates of organs induced by the tracers. Organ uptakes (% of injected activity/ml) varied from 6.2 x 10(-3 /red marrow to 3.1 X 10(-2)/liver for 99Tcm-MAb and from 3.1 x 10(-2)/red marrow to 1.8 x 10(-1)/liver for 131I-MAb, one hour after injection. Calculated average residence times of organs for 99Tcm-labelled BW250/183 were in the range of physical mean-life of 99Tcm and from 71 to 95 h for 131I-B72.3 respectively. The average total absorbed dose from 99Tcm-MAb to the bone marrow was 0.01 and to the spleen 0.14 mGy/MBq and from 131I-MAb the corresponding values were 0.48 and 10.76 mGy/MBq. This double-tracer technique provides information from two antibodies having different kinetic behaviour and may facilitate in distinguishing various antigens in targeting and control MAb applications.

Importance of intra-therapy single-photon emission tomographic imaging in calculating tumour dosimetry for a lymphoma patient

The dosimetry for two, similarly sized tumours in a lymphoma patient being treated with non-bone marrow ablative, monoclonal antibody therapy is reported. The 45-year-old man was infused with 2.48 GBq (67 mCi) of 131I-labelled MB-1. Prior to therapy, a time series of diagnostic conjugate-view images and a radionuclide transmission scan were obtained and processed to obtain time-activity curves. Starting 2 days after the therapeutic infusion of radioactivity, a second conjugate-view time series was obtained. At that time, a quantitative single-photon emission tomography (SPET) acquisition was also carried out. Pre- and post-therapy X-ray computed tomography scans demonstrated a percentage reduction in volume for the right tumour which was 3.8 times that for the left tumour. In contrast, diagnostic conjugate views by themselves estimated the absorbed dose to be the same for the two tumours. Addition of therapy conjugate-view data increased the right-over-left ratio but only to 1.22. Normalizing either time-activity series by the intra-therapy SPET results increased the ratio to greater than 1.5. We assume here that a differential dose is correct according to the differential tumour shirnkage. One can further assume that the largest ratio corresponds most certainly to the most accurate dosimetric method. Other assumptions are possible. While additional study is essential, data from this patient suggest that the preferred dosimetric method is intra-therapy SPET normalization of either time series.

Activity quantitation in SPECT: A study of prereconstruction Metz filtering and use of the scatter degradation factor

A study of activity quantitation with prereconstruction Metz filtering and use of the scatter degradation factor (SDF) to numerically correct for scatter was conducted. The ratio of the count rate per unit activity for source locations within a 30 x 23-cm water-filled tub phantom to the count rate per unit activity for Tc-99m point sources of known activity imaged in air was used to judge the accuracy of activity determination. The investigation was conducted for certain locations within the tub when it was uniformly filled with Tc-99m activity, and for the same locations at the center of 5, 4, 3, and 2-cm diam, hot spheres imaged in a cold background. The source locations were the center, and one-fourth, one-half, and three-fourths the major axis. Various methods of combining the conjugate views for use with prereconstruction attenuation correction (arithmetic and geometric mean), and extent to which the Metz filter followed the inverse filter before rolling off to suppress noise were investigated. Without Metz filtering, attenuation correction was performed using a transmission curve that included buildup. With Metz filtering, the good-geometry attenuation coefficient was used and the combined views were scaled by the SDF calculated for the average body thickness. Depending on the size of the sphere and the extent to which the inverse filter was followed, Metz filtering combined with use of the SDF improved the accuracy of activity quantitation.

Restoration of combined conjugate images in SPECT: comparison of a new Wiener filter and the image-dependent Metz filter

Two image-dependent restoration filters were applied to projection image sets obtained with single-photon-emission computed tomography (SPECT). Wiener and Metz restorations of combined conjugate views are compared to each other, Wiener restoration of individual projection images, and one-dimensional Butterworth smoothing. The combined view restoration filters adapt to the average thickness of the object by estimating a modulation transfer function (MTF) for that thickness. Simulated Tc-99m liver-spleen studies with randomly placed cold spot tumors, a projector which accounts for the spatially variant blurring in SPECT, and a Poisson noise generator are used to compute simulated projection image sets. These sets are filtered and reconstructed using the method of intrinsic attenuation correction of Tanaka et al. (1984). Cold spot contrast, automated receiver operator characteristic (ROC) analysis of cold spot detectability, and the normalized mean squared error (NMSE) are used to compare the four processing methods. Little difference is noted between the three restoration methods. However, the restoration filters all yield noticeably better ROC and NMSE results than the one-dimensional smoothing. Inspection of the three-dimensional MTF derived from reconstructions of point sources indicates that the restoration filters substantially reduce the low-frequency degradation which is primarily due to scatter.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Artefact reduction in dual-radionuclide subtraction studies

A method is proposed which significantly reduces the artefacts commonly experienced in dual radionuclide subtraction studies. Images of two radionuclides recorded simultaneously differ in resolution, sensitivity and attenuation. Also, one image will include scatter from the second higher-energy radionuclide. As a result severe artefacts are likely to occur when the two images are subtracted. In order to minimise the depth dependence of resolution, attenuation and scatter, the geometric mean of conjugate views was considered. From experimental work with activity placed in a depth of water it was demonstrated that the number and spatial distribution of scattered photons recorded in any energy window could be accurately predicted from the geometric mean image recorded in the photopeak. This prediction was accurate, independent of the depth of the source in water for a range of phantom dimensions. Differences in the instrument sensitivity and resolution at different energies can also be readily compensated for by using geometric mean images, as can differences due to the variation in attenuation. In practice three factors can be experimentally determined for any pair of radionuclides: a scatter ratio, a scatter function and a resolution compensation function. These data are then used to improve the dual-radionuclide subtraction analysis. The ability of the technique to significantly reduce subtraction artefacts has been demonstrated in phantom studies.

EMISSION-COMPUTED TOMOGRAPHY AND ITS APPLICATION TO IMAGING OF ACUTE MYOCARDIAL INFARCTION IN INTACT DOGS USING TC-99M PYROPHOSPHATE

The techniques of emission-computed tomography have been used to obtain in vivo quantitative estimates of the three-dimensional distribution of gamma-emitting radionuclides in dog hearts. Conjugate views, obtained for 60 equiangular projections around 360 degrees by rotating the object in front of a gamma camera, were used to reconstruct multiple-level emission transaxial images for various test objects, and for dogs with surgically induced acute myocardial infarcts. Corrections for attenuation were performed in the backprojection step of the convolution algorithm used for reconstruction. Quantitative estimates of the spatial extent and concentration of activity were obtained to within 10--15% rms error. Correlations were obtained between the radionuclide and histopathologic estimates of the extent and location of infarction.

Computed Transaxial Imaging Using Single Gamma Emitters

Emission computed tomography (ECT) studies were performed on test objects and dogs. Conjugate views were obtained for 60 to 120 projections equispaced around 360 degrees by rotation of the subjects in front of a gamma camera. A convolution reconstruction algorithm in which gamma ray attenuation corrections are included in the backprojection step were used to reconstruct the emission images. Reconstructions of x-ray transmission data provided data for gamma ray attenuation corrections of the emission images of 99mTc-pyrophosphate uptake in dogs. Reconstructed images of test objects show spatial resolution uniformity, and attenuation corrections enable estimation of relative activity densities to within 10--15% rms errors, thus demonstrating quantitative imaging capabilities of emission CT.