Biomedical subjects

Yi-Hwa Liu

Publications and source records attributed to Yi-Hwa Liu.

9 recordsLinked to original sources

PubMed2007

[18F]Fluorodeoxyglucose as a memory marker of transient myocardial ischaemia.

BACKGROUND: Experimental data have shown that glucose utilization increases during acute myocardial ischaemia, and may persist for up to 24 h. Whether fluorodeoxyglucose (FDG) uptake can be imaged as a memory marker of ischaemia in humans is unknown. METHODS: Patients with mild-to-moderate ischaemia on exercise single photon emission computed tomography (SPECT) myocardial perfusion imaging (MPI) underwent repeat exercise testing within 1-2 weeks. Positron emission tomography (PET) was performed after injection of FDG 60 min post-exercise. SPECT and PET images were assessed visually, aided by circumferential profile-based analysis modified for 'hot-spot' imaging. RESULTS: Twelve men with stress SPECT ischaemia (mean age, 69 years; nine with known coronary artery disease) were studied. The mean rate-pressure products for the first (SPECT) and second (FDG PET) exercise tests were similar (22,841+/-7321 vs. 22,680+/-7393 mmHg x bpm, P=NS). Overall, six of 12 patients studied had evidence of FDG uptake. The extent of ischaemia on SPECT was similar in FDG positive and FDG negative patients (summed difference score 10.6+/-6.9 vs. 8.0+/-1.6, P=NS). All patients with a positive FDG scan had uptake in either an ischaemic SPECT region or in a territory with known CAD by angiography. CONCLUSION: Regional myocardial uptake of FDG is enhanced even when injected 1 h post-exercise stress in a subset of patients with ischaemia on exercise SPECT MPI. The ability to image FDG uptake injected 1 h after an ischaemic episode suggests the potential utility of FDG as a memory marker of transient ischaemia.

Aged↗

PubMed2006

Aperture collimation correction and maximum-likelihood image reconstruction for near-field coded aperture imaging of single photon emission computerized tomography.

Coded aperture (CA) imaging originally developed in X-ray astronomy has not been widely used in nuclear medicine due to the decoding complexity of near-field CA images. In this paper, we present a near-field CA imaging technique and image reconstruction method for high sensitivity and high resolution single photon emission computerized tomography (SPECT). Our approach makes three contributions. First, a correction method for the aperture collimation effect is used to eliminate the near-field artifacts without dual acquisitions of mask and anti-mask images. Second, a maximum-likelihood expectation-maximization (MLEM) deconvolution method is used to restore CA images. Finally, a new MLEM-based algorithm is used to partially reconstruct three-dimensional (3-D) objects from a single projection of CA images. Experiments conducted using a dual-head SPECT system equipped with a parallel-hole collimator and a CA module show a tenfold increase in count sensitivity and significant improvement in image resolution with CA collimation as compared to parallel-hole collimation. Experiments conducted using the same dual-head SPECT system equipped with a pinhole collimator show that when the object is closer to the pinhole collimator the CA image resolution is only slightly inferior to the pinhole collimated image. We found that the MLEM deconvolution method provides an inherent nonnegativity constraint on pixel values and remarkably reduces background activities of CA images. The MLEM reconstruction algorithm for CA images is capable of reconstructing 3-D objects from a single projection and can be potentially extended to full 3-D SPECT reconstruction for CA images.

Algorithms↗

PubMed2005

A new method for SPECT quantification of targeted radiotracers uptake in the myocardium.

We developed a new method for absolute quantification of targeted radiotracers uptake in the myocardium using hybrid SPECT/CT and an external reference point source. A segmentation algorithm based on the level set was developed to determine the endocardial edges from CT, which were subsequently applied to the physically co-registered SPECT. A 3-D Gaussian fitting method was applied for quantification of the external point source. The total targeted radiotracer activity in the myocardium was normalized to that in the point source to calculate the absolute uptake of targeted radiotracer in the myocardium. Preliminary validation was performed in rats with ischemia-induced angiogenesis. The quantified in vivo radiotracer uptake was compared to the postmortem tissue radioactive well-counting of the myocardium. Our methods worked well for identification of the endocardial edges. Quantification of the focal uptake was consistent with the well-counting data. Our methods may have the potential of providing precise absolute quantification of targeted radiotracer uptake in the myocardium.

Animals↗

PubMed2003

Comparison of 16-frame and 8-frame gated SPET imaging for determination of left ventricular volumes and ejection fraction.

Electrocardiographic (ECG) gated single-photon emission tomography (SPET) allows for simultaneous assessment of myocardial perfusion and left ventricular (LV) function. Presently 8-frame per cardiac cycle ECG gating of SPET images is standard. The aim of this study was to compare the effect of 8-frame and 16-frame gated SPET on measurements of LV volumes and to evaluate the effects of the presence of myocardial perfusion defects and of radiotracer dose administered on the calculation of LV volumes. A total of 86 patients underwent technetium-99m SPET myocardial perfusion imaging using 16-frame per cardiac cycle acquisition. Eight-frame gated SPET images were generated by summation of contiguous frames. Left ventricular end-diastolic volume (EDV), end-systolic volume (ESV) and ejection fraction (EF) were calculated from the 16-frame and 8-frame data sets. The patients were divided into groups according to the administered dose of the radiotracer and the size of the perfusion defect. Results. Sixteen frame per cardiac cycle acquisition resulted in significantly larger EDV (122+/-72 ml vs 115+/-68 ml, P<0.0001), smaller ESV (64+/-58.6 ml vs 67.6+/-59.5 ml, P<0.0001), and higher LVEF (55.3%+/-18% vs 49%+/-17.4%, P<0.0001) as compared to 8-frame SPET imaging. This effect was seen regardless of whether a high or a low dose was administered and whether or not significant perfusion defects were present. This study shows that EDV, ESV and LVEF determined by 16-frame gated SPET are significantly different from those determined by 8-frame gated SPET. The radiotracer dose and perfusion defects do not affect estimation of LV parameters by 16-frame gated SPET.

Adult↗

PubMed2003

Electromechanical mapping for detecting myocardial viability and ischemia in patients with severe ischemic cardiomyopathy.

This study was designed to evaluate several electromechanical mapping parameters for assessment of myocardial viability and inducible ischemia as defined by dipyridamole single-photon emission computed tomographic (SPECT) imaging at rest in patients with severe ischemic cardiomyopathy. Unipolar voltage, normalized unipolar voltage, bipolar voltage, and fragmentation were compared with tracer uptake at rest and reversibility on stress or rest quantitative technetium-99m sestamibi SPECT imaging in 32 patients with severe ischemic cardiomyopathy (left ventricular ejection fraction 0.24 +/- 0.08). In dysfunctional myocardial segments, logistic regression showed unipolar voltage, normalized unipolar voltage, and bipolar voltage to be predictive of viable myocardium (> or = 60% tracer uptake at rest) and was significantly higher in viable than in nonviable segments (p <0.01). A unipolar voltage of > or = 7.1 mV was the best predictor of viable myocardium. In dysfunctional viable segments, unipolar voltage was significantly higher in reversible than in fixed segments (p <0.001), and a unipolar voltage of > or = 8.5 mV had optimal power for identifying reversibility on dipyridamole SPECT imaging. We conclude that in patients with severe ischemic cardiomyopathy, unipolar voltage can identify viable from nonviable myocardium and reversible from fixed viable defects as defined by dipyridamole technetium-99m sestamibi SPECT imaging.

Aged↗

PubMed2002

Correlation of myocardial p-(123)I-iodophenylpentadecanoic acid retention with (18)F-FDG accumulation during experimental low-flow ischemia.

UNLABELLED: Myocardial ischemia is associated with reduced free fatty acid (FFA) beta-oxidation and increased glucose utilization. This study evaluated the potential of dynamic SPECT imaging of a FFA analog, p-(123)I-iodophenylpentadecanoic acid (IPPA), for detection of ischemia and compares retention of IPPA with (18)F-FDG accumulation. METHODS: In a canine model of regional low-flow ischemia (n = 9), serial IPPA SPECT images (2 min per image) were acquired over 52--90 min. In a subset of dogs (n = 6), (18)F-FDG was injected after completing SPECT imaging and allowed to accumulate for 40 min before killing the animals. Flow was assessed with radiolabeled microspheres. Myocardial metabolism was evaluated independently by selective coronary arterial and venous sampling. RESULTS: Serial IPPA SPECT images showed an initial defect in the ischemic region (0.70% plus minus 0.03% ischemic-to-nonischemic ratio), which normalized within 48 min because of the slower IPPA clearance from the ischemic region (t(1/2) = 54.2 plus minus 3.3 min) relative to the nonischemic region (t(1/2) = 36.7 plus minus 5.6 min) (P < 0.05). Delayed myocardial IPPA and (18)F-FDG activities were correlated (r = 0.70; n = 576 segments), and both were maximally increased in segments with a moderate flow reduction (IPPA, 151% of nonischemic; (18)F-FDG, 450% of nonischemic; P < 0.05). CONCLUSION: Serial SPECT imaging showed delayed myocardial clearance of IPPA in ischemic regions with moderate flow reduction, which lead to increased late myocardial retention of IPPA. Retention of IPPA correlated with (18)F-FDG accumulation, supporting the potential of IPPA as a noninvasive marker of ischemic myocardium.

Animals↗

PubMed2002

Differential effect of 180 degrees and 360 degrees acquisition orbits on the accuracy of SPECT imaging: quantitative evaluation in phantoms.

UNLABELLED: A circular 180 degrees acquisition orbit is considered standard for cardiac SPECT imaging. Theoretically, a 360 degrees acquisition orbit is preferred because of more complete Fourier spectral information on projection data. The differential effect of 180 degrees and 360 degrees acquisition orbits on image accuracy (homogeneity and defect size) was assessed quantitatively in phantom studies. METHODS: SPECT imaging with a dual-head gamma camera was performed on normal cardiac phantoms filled with a (99m)Tc solution, using 180 degrees and 360 degrees circular acquisition orbits. The phantoms were placed in the center of the orbit and at 5, 10, and 15 cm off center. Fillable defect inserts of different sizes were placed in the phantom to simulate myocardial perfusion defects. The homogeneity of count distribution in short-axis slices of the normal phantom was analyzed as the percentage of variability. Defects were quantified as a percentage of the entire phantom volume using circumferential count profiles and normal reference profiles. RESULTS: When normal phantoms were placed in the center of the orbit, percentage variability was not different whether a 180 degrees or 360 degrees acquisition orbit was used (4.2% +/- 0.1% vs. 4.4% +/- 0.2%, P = not statistically significant). However when normal phantoms were placed off center, SPECT imaging with a 180 degrees acquisition orbit showed increasing inhomogeneity, both visually and quantitatively (e.g., percentage variability for the 15-cm off-center position was 10.8% +/- 0.1% (P < 0.0001). SPECT imaging with a 360 degrees acquisition orbit showed similar homogeneity visually and quantitatively, whether the phantom was placed in or off the center (e.g., percentage variability for the 15-cm off-center position was 4.6% +/- 0.5%, P = not statistically significant). Quantification of phantom defects acquired with a 180 degrees orbit showed increasing overestimation of defect sizes with increasingly off-center positions. Quantification of phantom defects acquired with a 360 degrees orbit showed no effect from progressively off-center positions, although phantom defect sizes were mildly underestimated. CONCLUSION: SPECT images acquired with a 180 degrees orbit may have significant erroneous inhomogeneity and overestimation of defect size, in particular when the target object is off the center of the orbit, as is commonly seen in clinical cardiac imaging. In contrast, SPECT images acquired with a 360 degrees orbit may provide more accurate quantitative information.

Heart↗

PubMedDate not supplied

New hybrid count- and geometry-based method for quantification of left ventricular volumes and ejection fraction from ECG-gated SPECT: methodology and validation.

BACKGROUND: We have previously developed a new method for quantitative assessment of left ventricular (LV) volumes and ejection fraction (EF) from electrocardiography-gated single photon emission computed tomography (SPECT). The aims of this study were to present the methodology, to validate the gated SPECT cardiac quantification (GSCQ) method in phantoms and patients, and to determine normal values of LVEF. METHODS AND RESULTS: A simple thresholding technique was used to generate binary images from nongated SPECT images. The K-means cluster classification algorithm was used to separate the LV region from non-LV regions on the binary images. A count- and geometry-based algorithm was applied to define endocardial and epicardial boundaries for calculation of LV volumes and LVEF. Overall correlation between GSCQ-quantified volumes and actual phantom volumes was good ( r = 0.97 and standard error of estimation (SEE) = 9.99 mL for normal phantoms, r = 0.99 and SEE = 6.97 mL for phantoms with defects). In patient studies, LVEF derived by GSCQ from SPECT and from equilibrium radionuclide angiography also showed good correlation ( r = 0.90 and SEE = 6.2%). The lower limit of normal LVEF from 8-frame gated SPECT by use of GSCQ was 45%. Quantification of LVEF by the GSCQ method was highly producible and was not significantly affected by the presence of myocardial perfusion defects or intense gastrointestinal activity. CONCLUSIONS: The GSCQ method provides reliable and consistent assessments of LV volumes and EF. This methodology is less affected by intense gastrointestinal activity than other methods.

Adult↗

PubMedDate not supplied

Clinical validation of SPECT attenuation correction using x-ray computed tomography-derived attenuation maps: multicenter clinical trial with angiographic correlation.

BACKGROUND: Nonuniform attenuation artifacts cause suboptimal specificity of stress single photon emission computed tomography (SPECT) myocardial perfusion images. In phantoms, normal subjects, and patients suspected of having coronary artery disease (CAD), we evaluated a new hybrid attenuation correction (AC) system that combines x-ray computed tomography (CT) with conventional stress SPECT imaging. METHODS AND RESULTS: The effect of CT-based AC was evaluated in phantoms by assessing homogeneity of normal cardiac inserts. AC improved homogeneity of normal cardiac phantoms from 11% +/- 2% to 5% +/- 1% (P < .001). Attenuation-corrected normal patient files were created from 37 normal subjects with a low likelihood (<3%) of CAD. The diagnostic performance of AC for detection of CAD was evaluated in 118 patients who had stress technetium 99m sestamibi or tetrofosmin stress SPECT imaging and coronary angiography. SPECT images with and without AC were interpreted by 4 blinded readers with different interpretative attitudes. Overall, AC improved the diagnostic performance of all readers, particularly the normalcy rate. The degree of improvement depended on interpretative attitude. Readers prone to high sensitivity or with less experience had the greatest gain in the normalcy rate, whereas a reader prone to higher specificity had improvements in sensitivity and specificity but not the normalcy rate. Importantly, improvement of one diagnostic variable was not associated with worsening of other variables. CONCLUSION: CT-based AC of SPECT images consistently improved overall diagnostic performance of readers with different interpretive attitudes and experience. CT-based AC is well suited for routine use in clinical practice.

Angiography↗