Gated blood-pool emission tomography: a new technique for the investigation of cardiac structure and function

ECG-gated single-photon emission-computed tomography of the intracardiac blood pool is a new technique that has not previously been widely applied. It involves the acquisition of ECG-gated images of the intracardiac blood pools labelled with sodium pertechnetate Tc 99m in 32 projections around the left-anterior hemithorax using a rotating gamma camera. From these images, tomographic sections are reconstructed orthogonal to the long axis of the left ventricle. The heart is therefore imaged three dimensionally, and more extensive information is obtained than in planar radionuclide ventriculography where imaging is usually restricted to only a single projection. Both structure and function can be studied, and the left-ventricular volume and ejection fraction, and wall motion are obtained. Of 50 patients studied, 7 cases are illustrated in order to show normal findings, examples of wall motion that were not shown by planar-contrast and radionuclide ventriculography, examples of the localisation of ventricular hypertrophy, and a comparison between blood-pool and 201TI myocardial tomography.     

Gamma camera emission tomography using radiolabelled antibodies

Single photon emission computed tomography (SPECT) of 52 patients injected with ¹³¹I and ¹¹¹In labelled monoclonal antibodies has been undertaken. Patients with tumors within the thorax or lower abdomen were imaged 48–72h following administration of 80 MBq ¹³¹I or ¹¹¹In labelled monoclonal antibody. Tumour detection from the reconstructed views was compared with that from the planar images. Studies of patients injected with ¹³¹I labelled antibodies required long data collection times otherwise image quality was unsatisfactory. Emission tomography using ¹¹¹In labelled antibodies, provided high quality reconstructed images using data collection times acceptable for most patients, and tumour deposits not confidently detected on planar images were clearly visualised in the axial views. These studies demonstrate the potential of radiolabelled antibody emission tomography.     

Parametric phase display for biventricular function from gated cardiac blood pool single-photon emission tomography

Complete assessment of biventricular function from planar ECG-gated cardiac blood pool studies has been limited because of the overlap of adjacent activity-containing structures. Theoretically, single-photon emission tomography (SPET) can be used to comprehensively evaluate both ventricles by isolating them from surrounding anatomy. However, an enormous amount of parametric data is generated from gated SPET studies, and much of it is diagnostically irrelevant for ventricular wall motion analysis. To compress this information to a more easily interpretable format, a two-dimensional parametric display has been developed. Fourier analysis of short-axis tomograms from a gated cardiac blood pool SPET study generates three-dimensional, first-harmonic phase data. Circumferential profile data from the parametric tomograms of the right and left ventricle are mapped onto a two-dimensional polar display. This method is demonstrated in a normal patient and in three patients with abnormal ventricular contraction patterns and appears to have potential application for the analysis and characterization of biventricular wall motion. Correspondence to: D.R. Neumann     

Multigated blood-pool tomography: new method for the assessment of left ventricular function

A technique for the semiautomatic calculation of left ventricular volumes from multigated blood-pool tomograms (MGBPT) was tested in a series of 12 patients undergoing contrast ventriculography within 48 hr of gated tomography. The parameters necessary for the calculation of volume were developed in a chest phantom study performed with a series of 99mTc-filled balloons representing the right and left ventricles. The images were analyzed for volume using a percentage of peak count-threshold of the left ventricular balloon. This technique resulted in a correlation of r = 0.99 of the calculated to the true phantom volumes (y = 0.87x + 27.4, p less than 0.01, s.e.e. = 7.87 ml). The patient studies were recorded at 16 frames/cardiac cycle at each of 60 angles over a 360 degree rotation. Reconstructed data were presented in an endless loop cine format producing a set of sequential "beating tomographic slices" in the transverse, apical four-chamber, short-axis, and long-axis oblique views. Measurements of end systolic volume (y = 0.79x + 30, r = 0.93, p less than 0.001, s.e.e. = 24 ml), end-diastolic volume (y = 0.63x + 60, r = 0.94, p less than 0.0001, s.e.e. = 20 ml) and ejection fraction (y = 0.88x - 0.02, r = 0.92, p less than 0.001, s.e.e. = 0.08) determined from the semiautomated volume method correlated well with those determined by left ventricular contrast angiography. A qualitative comparison of MGBPT, planar imaging, and left ventricular angiography in 12 patients revealed that the visual assessment of wall motion using the 16-frame tomographic slices had significant advantages over planar and single plane angiographic data in the identification of inferior, basal, and septal wall motion abnormalities as well as the extent of involvement by aneurysm formation. A quantitative comparison of wall motion in the long-axis oblique view of the MGBPT to the RAO 30 degree ventriculogram (y = 0.74x + 8.7, r = 0.82, p less than 0.0001, s.e.e. = 14%) confirmed the qualitative similarity of these two views. We conclude that MGBPT is promising as a method for accurately measuring left ventricular volumes and assessing regional wall motion.     

A new iterative reconstruction technique for attenuation correction in high-resolution positron emission tomography

A new iterative reconstruction technique (NIRT) for positron emission computed tomography (PET), which uses transmission data for nonuniform attenuation correction, is described. Utilizing the general inverse problem theory, a cost functional which includes a noise term was derived. The cost functional was minimized using a weighted-least-square maximum a posteriori conjugate gradient (CG) method. The procedure involves a change in the Hessian of the cost function by adding an additional term. Two phantoms were used in a real data acquisition. The first was a cylinder phantom filled with uniformly distributed activity of 74 MBq of fluorine-18. Two different inserts were placed in the phantom. The second was a Hoffman brain phantom filled with uniformly distributed activity of 7.4 MBq of¹⁸F. Resulting reconstructed images were used to test and compare a new iterative reconstruction technique with a standard filtered backprojection (FBP) method. The results confirmed that NIRT, based on the conjugate gradient method, converges rapidly and provides good reconstructed images. In comparison with standard results obtained by the FBP method, the images reconstructed by NIRT showed better noise properties. The noise was measured as rms% noise and was less, by a factor of 1.75, in images reconstructed by NIRT than in the same images reconstructed by FBP. The distance between the Hoffman brain slice reconstructed by FBP and the perfect PET Hoffman brain slice created from the MRI image was 0.526, while the same distance for the Hoffman brain slice reconstructed by NIRT was 0.328. The NIRT method suppressed the propagation of the noise without visible loss of resolution in the reconstructed PET images.     

A brain phantom for studying contrast recovery in emission computerized tomography

A brain phantom is described that is characterized by a high anatomical definition and by the possibility of varying the internal contrast with the use of a single radioactive solution. The experimental work was done with a single-photon emission computerized tomographic (SPET) rotating camera. The phantom was used to study the contrast recovery of both the filtered back-projection and an iterative reconstruction algorithm. Moreover, it was also used to find a cross-calibration factor between activity concentrations in the SPET slices and an external reference.     

Assessment of cardiac function and left ventricular regional wall motion by 99mTc multigated cardiac blood-pool emission computed tomography]

Forty-three patients underwent the analysis of left and right ventricular (LV and RV) volumes, and LV regional wall motion by multigated cardiac blood pool single photon emission computed tomography (SPECT) with 99mTc. To calculate the cardiac volume correctly, the optimal cutoff level in relation to background level was first obtained by a phantom study. Left ventricular end-diastolic, end-systolic volume (EDV and ESV) and ejection fraction (EF) calculated thus with SPECT were correlated well with the data obtained with left ventriculography (LVG) and magnetic resonance imaging (MRI), especially using horizontal long axial image. RV stroke volume (SV) without shunt or valvular diseases was also correlated well with that of LV when it was calculated using horizontal long axial image. However, SV ratio (LVSV/RVSV) was not necessarily ideal numerical 1. In addition LV wall motion was evaluated by multicontour systolic display and phase analysis in SPECT and gated planar images. The results obtained with SPECT were better correlated with those of LVG than gated planar images. It is concluded that multigated cardiac blood pool SPECT is a clinically useful method for an evaluation of cardiac function and left ventricular regional wall motion.     

Assessment of left ventricular function by gated cardiac blood-pool emission computed tomography using a rotating gamma camera

To elucidate the usefulness of gated cardiac blood-pool single photon emission CT (SPECT) with Tc-99m for the evaluation of left ventricular (LV) global and regional functions, 18 patients with coronary artery disease were studied. Thirty-two gated projection images were obtained over 360-degree at 16 frames per cardiac cycle. As LV volume was calculated by integrating the numbers of voxels which constituted LV and multiplying by the volume of a single voxel (0.1143 ml), we performed phantom studies to determine the appropriate cut-off level to detect LV outline. These cut-off levels were affected by the background activity and organ volume itself. So we constructed Volume-Cut-Level-Curve at each background activity. In clinical studies, short axis images which constituted LV were selected and provisional LV volumes were calculated at the cut-off levels of 45, 50 and 55%. These volumes were plotted on the Volume-Cut-Level-Curve and the true cut-off levels were obtained to calculate LV end-diastolic or end-systolic volume (EDV, ESV). The cut-off levels were different at every patient and ED or ES. EDV, ESV and LV ejection fraction obtained by SPECT were correlated well with those obtained by contrast ventriculography (LVG) (r = 0.89, 0.94, 0.94 each, p less than 0.01). For the LV wall motion analysis, LVGs obtained at two projections were compared with SPECT or gated cardiac blood-pool planar imaging (Planar) in 5 segments. In addition to visual comparison, wall motion scores (WMS) based on the degree of wall motion abnormality were calculated in each segment. Correlation of WMS between LVG and SPECT (r = 0.84) was significantly (p less than 0.01) superior to that between LVG and Planar (r = 0.62). Especially in SPECT, wall motion analyses at septal and infero-posterior segments were superior to those in Planar. Although gated SPECT requires relatively long time to perform, it is a useful method to detect LV global and regional functions.     

Complementarity of magnetic resonance spectroscopy,positron emission tomography and single photon emission tomography for the in vivo investigation of human cardiac metabolism and neurotransmission

The three techniques allowing the noninvasive study of cardiac metabolism, namely magnetic resonance spectroscopy (MRS), positron emission tomography (PET) and single photon emission computed tomography (SPET), all use external detection with stable or radioactive isotopes. These techniques yield different information. PET is quantitative and very sensitive, and therefore only tracer amounts of molecules need to be injected. It allows neurotransmitters and receptors to be studied and a global view of metabolism (oxygen consumption, glucose and fatty acid utilization) to be obtained. SPET also has good sensitivity, but uses gamma-emitting isotopes of heteroatoms. Their longer half-lives allow follow-up for hours or days. MRS is based on stable elements with high (hydrogen 1, phosphorus 31, fluorine 19 ...) or low (carbon 13, Deuterium) natural abundance. It has very low sensitivity and only millimolar concentrations of substrates can be detected, but various parts of metabolism can be studied. The in vivo measurement of myocardial concentration of substances has many problems that are common to all three techniques (measurement of the volume, measurement of the quantity of each molecule, resolution, partial volume effect, improvement of the signal-to-noise ratio, movement of the organ). The complementarity of the techniques is illustrated by their applications to the study of cardiac metabolism. For instance, the energy metabolism can be studied by³¹P-MRS, which detects the high-energy compounds ATP and phosphocreatine, and¹³C-MRS yields information on the tricarboxylic acid cycle activity. PET and SPET allow the utilization of fatty acids, the normal fuels of the heart, to be studied. During ischaemia, PET with¹⁸F-fluorodeoxyglucose (¹⁸FDG) can determine the glucose consumption and¹H-MRS shows the increase in lactic acid, reflecting anaerobic glycolysis. Comparison of the use of acetate labelled with¹¹C for PET or¹³C for MRS shows the potentials and limitations of each technique. Myocardial perfusion can be evaluated directly with various PET tracers or indirectly with thallium 201 or various technetium-99m-labelled tracers by SPET. No MRS marker of perfusion is so far clinically available. Mainly SPET and PET are used clinically for the investigation of ischaemic heart disease as well as cardiomyopathies, but some initial results using³¹P-MRS are being obtained.     

Scatter modelling and compensation in emission tomography

In nuclear medicine, clinical assessment and diagnosis are generally based on qualitative assessment of the distribution pattern of radiotracers used. In addition, emission tomography (SPECT and PET) imaging methods offer the possibility of quantitative assessment of tracer concentration in vivo to quantify relevant parameters in clinical and research settings, provided accurate correction for the physical degrading factors (e.g. attenuation, scatter, partial volume effects) hampering their quantitative accuracy are applied. This review addresses the problem of Compton scattering as the dominant photon interaction phenomenon in emission tomography and discusses its impact on both the quality of reconstructed clinical images and the accuracy of quantitative analysis. After a general introduction, there is a section in which scatter modelling in uniform and non-uniform media is described in detail. This is followed by an overview of scatter compensation techniques and evaluation strategies used for the assessment of these correction methods. In the process, emphasis is placed on the clinical impact of image degradation due to Compton scattering. This, in turn, stresses the need for implementation of more accurate algorithms in software supplied by scanner manufacturers, although the choice of a general-purpose algorithm or algorithms may be difficult.     

A publicly accessible Monte Carlo database for validation purposes in emission tomography

Monte Carlo (MC) methods provide ideal data sets to assess reconstruction and correction techniques in emission tomography (ET). Although several ET-dedicated MC codes are available, their use is hindered by the heavy computation burden required for high statistics simulations as well as by the need to adapt the code to the purpose of the individual user. In this work a publicly accessible database of MC-simulated ET data sets (the MC-ET database) was created and published on an Internet web site (), in order to provide MC-simulated data ready to be downloaded and used by researchers at different sites with similar evaluation purposes. At present, the MC-ET database provides direct access to MC-simulated raw data of unscattered, scattered and total events: (a) obtained by different MC codes, (b) relative to different radioactive sources, from simple geometrical phantoms to studies of normal and pathological subjects and (c) derived from different SPECT and PET scanners. The main features of the MC-ET data sets are: (a) validation by comparison with measured data, (b) classification according to pre-defined database characteristics, (c) common-use file format and (d) easy and free access and download.     

A new approach to positron emission tomography

A recently developed detection principle for gamma rays offers the prospect of improving the performance of positron emission tomographic scanners. This detection principle is based on the use of BaF₂ scintillator and photosensitive wire chambers. We present technical results obtained with a prototype detector. It is shown that the impact point of the gamma ray can be determined with a precision of a few mm and that the detection efficiency is 60% with a time resolution of 10 ns (FWHM). A scanner based on the new principle is described and its anticipated performance discussed.This article was presented at the 1st EEC workshop on accuracy determination in PET, January 19–20th. 1989 Pisa, Italy (COMAC-BME Concerted Project Characterization and Standardization of PET Instrumentation)     

Recovery correction for quantitation in emission tomography: a feasibility study

In emission tomography, the spread of regional tracer uptake to surrounding areas caused by limited spatial resolution of the tomograph must be taken into account when quantitating activity concentrations in vivo. Assuming linearity and stationarity, the relationship between imaged activity concentration and true activity concentration is only dependent on the geometric relationship between the limited spatial resolution of the tomograph in all three dimensions and the three-dimensional size and shape of the object. In particular it is independent of the type of object studied. This concept is characterized by the term ”recovery coefficient”. Recovery effects can be corrected for by recovery coefficients determined in a calibration measurement for lesions of simple geometrical shape. This method works on anatomical structures that can be approximated to simple geometrical objects. The aim of this study was to investigate whether recovery correction of appropriate structures is feasible in a clinical setting. Measurements were done on a positron emission tomography (PET) scanner in the 2D and 3D acquisition mode and on an analogue and digital single-photon emission tomography (SPET) system using commercially available software for image reconstruction and correction of absorption and scatter effects. The results of hot spot and cold spot phantom measurements were compared to validate the assumed conditions of linearity and stationarity. It can be concluded that a recovery correction is feasible for PET scanners down to lesions measuring about 1.5×FWHM in size, whereas with simple correction schemes, which are widely available, an object-independent recovery correction for SPET cannot be performed. This result can be attributed to imperfections in the commercially available methods for attenuation and scatter correction in SPET, which are only approximate. Received 22 June and in revised form 30 September 1999     

Noniterative sequential weighted least squares algorithm for positron emission tomography reconstruction

This paper proposes a new sequential weighted least squares (SWLS) method for positron emission tomography (PET) reconstruction. The SWLS algorithm is noniterative and can be considered as equivalent to the penalized WLS (PWLS) method under certain initial conditions. However, a full implementation of SWLS is computationally intensive. To overcome this problem, we propose a simplified SWLS as a reasonable alternative to the SWLS. The performance of this SWLS method is evaluated in experiments using both simulated and clinical data. The results show that the method can be advantageously compared with the original SWLS both in computation time and reconstruction quality.     

Bayesian image reconstruction for emission tomography based on median root prior

The aim of the present study was to investigate a new type of Bayesian one-step late reconstruction method which utilizes a median root prior (MRP). The method favours images which have locally monotonous radioactivity concentrations. The new reconstruction algorithm was applied to ideal simulated data, phantom data and some patient examinations with PET. The same projection data were reconstructed with filtered back-projection (FBP) and maximum likelihood-expectation maximization (ML-EM) methods for comparison. The MRP method provided good-quality images with a similar resolution to the FBP method with a ramp filter, and at the same time the noise properties were as good as with Hann-filtered FBP images. The typical artefacts seen in FBP reconstructed images outside of the object were completely removed, as was the grainy noise inside the object. Quantitatively, the resulting average regional radioactivity concentrations in a large region of interest in images produced by the MRP method corresponded to the FBP and ML-EM results but at the pixel by pixel level the MRP method proved to be the most accurate of the tested methods. In contrast to other iterative reconstruction methods, e.g. ML-EM, the MRP method was not sensitive to the number of iterations nor to the adjustment of reconstruction parameters. Only the Bayesian parameter had to be set. The proposed MRP method is much more simple to calculate than the methods described previously, both with regard to the parameter settings and in terms of general use. The new MRP reconstruction method was shown to produce high-quality quantitative emission images with only one parameter setting in addition to the number of iterations.     

Gated fluorine 18 fluorodeoxyglucose positron emission tomography: Determination of global and regional left ventricular function and myocardial tissue characterization

BACKGROUND: Our objectives were to investigate the accuracy of global and regional left ventricular (LV) function parameters determined from gated fluorine 18 deoxyglucose (FDG) positron emission tomography (PET) and to determine whether this approach complements viability imaging data for tissue characterization. Nongated FDG-PET is a clinical standard for viability imaging, but LV function is often determined with other techniques, which increases patient burden, expenditure, and co-registration errors. Better tissue characterization may be achieved if data were acquired with one test.Methods and results Forty-eight patients with LV dysfunction (including 35 with ejection fraction [EF] 相似文献   

Ventricular function during the acute rejection of heterotopic transplanted heart: Gated blood-pool studies

Twenty patients who had undergone a heterotopic heart transplant were studied prospectively to determine the relationship between rejection and ventricular dysfunction assessed from gated blood-pool studies. A fully automated method for detecting ventricular edges was implemented; its success rate for the grafted left and right ventricles was 94% and 77%, respectively. The parameters, peak ejection and filling rates, were calculated pixel per pixel using a two-harmonic Fourier algorithm and then averaged over the ventricular region of interest. Peak filling and ejection rates were closely related with the severity of the rejection, while the left ventricular ejection fraction was not. Peak filling rates of both ventricles were the indices closely related to the presence of moderate rejection. Despite the low number of patients, these data suggested that gated blood-pool-derived indices of ventricular function are associated with ventricular dysfunction resulting from myocarditis rejection. Radionuclide ventriculography provides parametric data which are accurate and reliable for the diagnosis of rejection.     

Radionuclides and radiopharmaceuticals for single-photon emission tomography, positron emission tomography and radiotherapy in Russia

The current status of the manufacture of radiopharmaceuticals for diagnostic and therapeutic application in Russia is discussed, consideration being given to various aspects of the production and distribution of radionuclides, radioisotope generators and kits as well as individual radiopharmaceuticals in different regions of the country. The major focus is on the recent developments in production technologies for therapeutic and single-photon emission tomography radionuclides, technetium chemistry and synthetic approaches for the labelling of compounds with short-lived positron emitters. The status of positron emission tomography and its application are considered. The major factors restricting the expansion of nuclear imaging techniques and radiotherapy in Russia are also discussed.     

Gated 99mTc-MIBI single-photon emission computed tomography for the evaluation of left ventricular ejection fraction: comparison with three-dimensional echocardiography

Objective  Parameters of left ventricular systolic function directly influence the management of patients with suspected coronary artery disease (CAD). Quantitative gated single-photon emission computed tomography (QGS; Cedars-Sinai Medical Center, Los Angeles, CA, USA) allows the computation of left ventricular ejection fraction (LVEF) from myocardial perfusion imaging studies which are frequently performed on patients with suspected CAD. Three-dimensional (3D) echocardiography is considered to be the echocardiographic “gold standard” for the quantification of LVEF. We sought to compare QGS with 3D echocardiography in the evaluation of EF in patients with suspected CAD. Methods  Ninety-one consecutive patients with suspected CAD, scheduled for coronary angiography, underwent rest electrocardiographic-gated technetium-99m methoxyisobutylisonitrile SPECT (G-SPECT) with measurement of LVEF by QGS and transthoracic 3D echocardiography with off-line measurement of LVEF (Tomtec 4D LV Analysis 1.1). The diagnosis of CAD was based on coronary angiography, performed on every patient. Results  Nine patients were excluded from the analysis owing to unsuitability for 3D echocardiography (8 patients) or G-SPECT (1 patient). In the remaining group of 82 patients, 71 (87%) had significant CAD, 34 (42%) had a history of myocardial infarction, and 50 (61%) had perfusion defects at rest G-SPECT images. The mean LVEF measured by QGS and 3D echocardiography was 53 ± 13% and 53 ± 10%, respectively. The mean difference in LVEF between 3D echocardiography and QGS was 0.1 ± 6.0% (P = 0.87), and the correlation between the values obtained by both methods was high (r = 0.88, P < 0.001). The largest discrepancies were observed in patients with small ventricular volumes. Conclusions  In patients undergoing diagnostic work-up for CAD, the measurement of LVEF by QGS algorithm provides high correlation and satisfactory agreement with the results of reference ultrasound method-3D echocardiography.     

Pre-targeted immunodetection in glioma patients: tumour localization and single-photon emission tomography imaging of [99mTc]PnAO-biotin

The imaging of cerebral gliomas with radiolabelled monoclonal antibodies (MoAbs) has been previously reported. However, previous studies have been hampered by the drawback of a low tumour to non-tumour ratio. In order to overcome this problem we have developed a three-step pre-targeting method using the avidin-biotin system. The rationale of this technique consists in vivo labelling of biotinylated MoAbs targeted onto tumour deposits, when most of the unbound antibodies have been cleared from the bloodstream as avidin-bound complexes. The anti-tenascin MoAb BC2, specific for the majority of gliomas, was biotinylated and 1 mg was administered i.v. in 20 patients with histologically documented cerebral lesions. After 24–36 h, 5 mg avidin was injected i.v. followed 24 h later by a third i.v. injection of 0.2 mg PnAO-biotin labelled with 15–20 tnCi technetium-99m. No evidence of toxicity was observed. Whole-body biodistribution was measured at 20 min, 3 h and 5 h post-injection. [^99mTc]PnAO-bio-tin had a fast blood clearance and was primarily excreted through the biliary system. A dedicated single-photon emission tomography system was used to acquire brain tomographic images 1–2 h after the administration of [^99mTc]PnAO-biotin. Tumours were detected in 15/18 glioma patients with a tumour to non-tumour ratio of up 14:1. This three-step method, based on the sequential administration of anti-tenascin MoAb BC2, avidin and [^99mTc]PnAO-biotin, can support computed tomography or magnetic resonance imaging for the diagnosis and follow-up of patients with glioma. Further studies are required to evaluate the potential of this technique for therapeutic application.