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Biomedical subjects

R A deKemp

Publications and source records attributed to R A deKemp.

10 recordsLinked to original sources
PubMed2001

Myocardial glucose utilization and optimization of (18)F-FDG PET imaging in patients with non-insulin-dependent diabetes mellitus, coronary artery disease, and left ventricular dysfunction.

UNLABELLED: In patients with non-insulin-dependent diabetes mellitus (NIDDM), FDG PET imaging is often problematic because of poor uptake of FDG. Different protocols have been used; however, these have not been directly compared in patients with NIDDM who have both coronary artery disease (CAD) and severe left ventricular (LV) dysfunction, for which defining viability is most relevant. The aim of this study was to better define the optimal means of FDG PET imaging, assessed by image quality and myocardial glucose utilization rate (rMGU), among 3 imaging protocols in patients with NIDDM, CAD, and severe LV dysfunction. METHODS: Ten patients with NIDDM, CAD, and severe LV dysfunction (mean ejection fraction, 29.8% +/- 7.1%) underwent dynamic FDG PET scanning using 3 different protocols: the standard protocol, consisting of oral glucose loading or a supplemental insulin bolus based on fasting glucose; the niacin protocol, consisting of pretreatment with niacin to lower free fatty acids; and the insulin clamp protocol, consisting of hyperinsulinemic euglycemic clamp. Image quality was satisfactory with at least 1 approach in 8 patients, who formed the primary analysis group. RESULTS: Myocardium-to-blood-pool ratios were significantly higher with the insulin clamp (standard, 1.7 +/- 1.2; niacin, 1.6 +/- 1.0; insulin clamp, 3.4 +/- 2.5 [P < 0.05 vs. standard and niacin]). Values for rMGU were higher with the insulin clamp (standard, 0.11 +/- 0.07 micromol/g/min; niacin, 0.12 +/- 0.11 micromol/g/min; insulin clamping, 0.22 +/- 0.12 micromol/g/min [P = 0.004 vs. standard and 0.07 vs. niacin]). CONCLUSION: The hyperinsulinemic euglycemic clamp yielded the highest FDG PET image quality and the highest rMGU in a comparison with the standard and niacin protocols in this difficult group of patients with NIDDM, CAD, and severe LV dysfunction. The hyperinsulinemic euglycemic clamp may be the preferred method for FDG PET viability imaging in this population. Larger clinical trials are needed to assess whether accuracy is greater with this approach.

Coronary Artery Disease↗
PubMed2000

Detection of serial changes in absolute myocardial perfusion with 82Rb PET.

UNLABELLED: Serial changes in myocardial perfusion may represent an important marker of disease progression or regression or the effects of therapy for patients with coronary artery disease (CAD). Quantitative methods have not been developed for the assessment of serial changes in perfusion. The objective of this study was to use receiver operator characteristic (ROC) analysis to determine the sensitivity and specificity of direct paired comparisons (DPCs) to detect changes in absolute myocardial perfusion measured with 82Rb PET. METHODS: Repeated dynamic 82Rb PET scans were obtained on 8 dogs at rest and during hyperemia induced with dobutamine (n = 4) or atrial pacing (n = 4). Radiolabeled microspheres were used to verify perfusion changes. Polar maps of absolute 82Rb retention and associated SD were estimated from the dynamic images. Paired comparisons were then performed using a t test on each of the 532 polar map sectors. Rest-rest and stress-stress differences were used to assess specificity and reproducibility, and stress-rest differences were used to assess sensitivity. RESULTS: 82Rb retention differences of 20% over baseline were detected with 85%-90% sensitivity and specificity, using the optimal DPC probability value and image smoothness. The average 82Rb retention differences correlated well with microspheres (r = 0.74; P = 0.001). Reproducibility of the mean retention values was 4.7% +/- 2.1%. As reproducibility varies, the DPC probability value can be adjusted to maintain specificity. These ROC results are directly applicable to other image modalities that produce measurements with similar SEs (3.7% +/- 0.9%). CONCLUSION: The developed method of DPCs is sensitive and specific for the detection of changes in absolute myocardial perfusion measured with 82Rb PET.

Animals↗
PubMed1998

Delay in revascularization is associated with increased mortality rate in patients with severe left ventricular dysfunction and viable myocardium on fluorine 18-fluorodeoxyglucose positron emission tomography imaging.

BACKGROUND: The identification of high-risk patients who require early revascularization has become increasingly important with the present emphasis on reducing health care resources. This is particularly relevant to health care systems with prolonged waiting times for interventions. Myocardial viability imaging with the use of fluorine 18-fluorodeoxyglucose (FDG) PET may help to identify high-risk patients with severe left ventricular dysfunction. The aim of this study was to evaluate the consequences of prolonged waiting time on cardiac outcomes in patients with left ventricular dysfunction directed to revascularization based on FDG PET imaging. METHODS AND RESULTS: Forty-six patients with coronary disease and an ejection fraction of < or = 35% were considered candidates for revascularization based on FDG PET viability imaging. Thirty-five of 46 patients were subsequently accepted for revascularization. Patients were divided into 2 groups based on the median waiting time after PET: an early group (< 35 days; n = 18) and a late group (> or = 35 days; n = 17). Preoperative mortality rates were significantly increased in the late group (4 of 17 [24%] versus 0 of 18 in the early group; P < 0.05). In postoperative follow-up (17 +/- 7 months), cardiac events occurred in 2 of 18 (11%) and 1 of 13 (7.8%) patients in the early and late groups, respectively. Left ventricular ejection fraction increased after early revascularization (24 +/- 7% to 29 +/- 8%, P < 0.001, baseline versus 3 months) but not in the late group (27 +/- 5% to 28 +/- 6%, P = NS). CONCLUSIONS: Preoperative FDG PET can be used to identify a high-risk group of patients who may benefit from early revascularization. A long waiting time for revascularization is associated with a high mortality rate and suggests that early revascularization is desirable after the identification of hibernating viable myocardium.

Aged↗
PubMed1997

F-18-fluorodeoxyglucose PET imaging alters clinical decision making in patients with impaired ventricular function.

The effect of F-18-fluorodeoxyglucose positron emission tomography imaging on decision making in the selection of patients with impaired ventricular function for revascularization was determined in 87 patients. In 57% of patients, positron emission tomography data influenced management decisions, indicating an important effect of myocardial viability determination on difficult therapy decisions in these patients.

Aged↗
PubMed1996

Automated determination of the left ventricular long axis in cardiac positron tomography.

Interpretation of emission tomographic images of the heart is typically performed using short-axis sections which are oriented perpendicular to the long axis of the left ventricle. A completely automated method is presented to find the orientation and length of the long axis in positron emission tomographic studies of the heart. The correlation coefficient is maximized between the measured transaxial images and an ellipsoid model of the left ventricular myocardium. The major axis of this fitted ellipsoid corresponds to the long axis of the left ventricle. The orientation and position of the long axis (with respect to the measured transaxial images) define two rotation angles and a 3D coordinate origin which are used to re-orient the transaxial images into a series of standard short-axis sections. The accuracy and precision of this technique are validated on phantom data as well as on patients with documented myocardial infarction. The transaxial and vertical long-axis rotation angles are determined with standard deviations of 3.3 degrees and 1.5 degrees, respectively. The 3D coordinate origin (centre) of the ellipsoid is accurate to within 1.5 mm on average. The estimated length of the left ventricle is accurate to within 3 mm. All parameters are insensitive to statistical noise found in typical 18F-fluorodeoxyglucose (FDG) patient studies. The technique produces accurate estimates even in the presence of moderate uptake defects in the lateral wall and septum. Apical defects in the uptake of FDG do not increase the variance of the length estimate. These results demonstrate that an ellipsoid model can be fitted accurately to the myocardium of the left ventricle. Standard short-axis sections are produced with no inter-operator or intra-operator variability because the technique is fully automatic.

Deoxyglucose↗
PubMed1994

Attenuation correction in PET using single photon transmission measurement.

The use of single photon transmission measurement with a rotating rod source has been evaluated to measure the attenuation correction factors in positron emission tomography (PET). The singles projections are resampled into the coincidence geometry using the detector positions and the rod source location. A nonparalyzable dead time correction algorithm was developed for the block detectors used in the McMaster PET scanner. This enables accurate attenuation correction factors (ACFs) to be computed using a wide range of source strengths for transmission scanning. Transaxial resolution is approximately 6 mm, which is comparable to emission scanning performance. Axial resolution is about 25 mm, with only crude source collimation. ACFs are underestimated by as much as 10% due to increased cross-plane scatter, compared to coincidence transmission accuracy. The response of the correction factors to object density is within 15%, when comparing singles transmission measurement to current coincidence transmission measurement. The major advantage of using singles transmission measurement is a dramatically increased count rate. A factor of 7 increase in count rate over coincidence scanning is possible with a 2-mCi transmission rod source. Uniformity of 2% in the transmission images is possible with this source strength and a 2-min acquisition. There are no randoms counted in singles transmission scans, which makes the measured count rate vary linearly with source activity. Singles detector dead time losses are approximately 6% in the detectors opposite a 2-mCi rod source.

Algorithms↗
PubMed1993

Automated in vivo quantification of emphysema.

A computer program to automatically determine lung volume and percentage of emphysema from computed tomographic (CT) chest sections was developed. To test it, the authors reviewed scans obtained in 89 patients. Any computer errors in identification of normal or emphysematous lungs were corrected manually by tracing the boundaries of the lungs or eliminating areas of nonemphysematous lung with a roller ball. The corrected values were compared with the uncorrected values. In 33 patients from the study group, lung volumes and the percentage of emphysema were calculated by using a currently available "voxel highlighting" program. Successful computerized analysis of entire lungs was performed in 1 minute, compared to more than 1 hour for manual analysis. Correlation was high (r = .99) between results obtained manually and those obtained with the computer. Although the difference between uncorrected and corrected values of the percentage of emphysema was statistically significant, this converted to a correction of only 0.1%. The computer program allowed quick, accurate, and reproducible quantification of emphysema.

Adult↗
PubMedDate not supplied

Potential utility of rubidium 82 PET quantification in patients with 3-vessel coronary artery disease.

BACKGROUND: Standard perfusion imaging may underestimate the extent of disease in 3-vessel coronary atherosclerosis. This study determined whether positron emission tomography quantification of perfusion reserve by use of rubidium 82 net retention defined a greater extent of disease than the standard approach in patients with 3-vessel disease. METHODS AND RESULTS: Rb-82 net retention was quantified as an estimation of absolute perfusion at rest and with dipyridamole stress by use of dynamic positron emission tomography imaging. The percent of abnormal myocardial sectors, as compared with a normal database, for a standard and quantification approach was determined. Twenty-three patients were evaluated. Defect sizes were larger in patients with 3-vessel disease (n = 13) by use of quantification methods: 44% +/- 18% of the myocardial sectors were abnormal by use of the standard approach versus 69% +/- 24% of sectors when measured by quantification of the stress-rest perfusion difference (P =.008). In patients with single-vessel disease (n = 10), defect sizes were smaller with quantification methods. CONCLUSIONS: Quantification of Rb-82 net retention to measure the stress-rest perfusion difference in the myocardium defined a greater extent of disease than the standard approach in this group of patients with triple-vessel disease. More accurate measurement of the extent of coronary artery disease could facilitate better risk stratification and identify more high-risk patients in whom aggressive intervention is required.

Aged↗
PubMedDate not supplied

Stress perfusion/metabolism imaging: a pilot study for a potential new approach to the diagnosis of coronary disease in women.

BACKGROUND: The diagnosis of coronary artery disease (CAD) in women continues to be a challenge. F-18 deoxyglucose (FDG) positron emission tomography (PET) has been used for detection of myocardial ischemia at rest. Little has been reported about FDG stress imaging. The aim of this pilot study was to assess stress FDG PET imaging for defining CAD in a group of women referred for chest pain. METHODS: Stress FDG imaging was performed in 19 women (mean age 59 +/- 10 years). All had abnormal stress testing before entering the study. FDG and 2-methoxy-2-methylpropyl isonitrile were injected at peak stress (treadmill n = 8, dipyridamole n = 11) followed by PET and single photon emission computed tomography image acquisitions. Myocardial ischemia was defined by regions that demonstrated both a defect on perfusion imaging and increased FDG uptake relative to uptake in normal perfusion zones. Defect/normal zone FDG ratios were also determined. Coronary angiography was performed on all patients. RESULTS: Average, or mean, body mass index was high at 29.2 +/- 5 kg/m2. Nine of 19 patients had significant CAD. Eight of 9 with CAD had FDG-defined ischemia. Nine of the 10 without CAD had negative FDG images (sensitivity 89%, specificity 90%). The average defect/normal zone FDG ratio was greater in patients with CAD than in those without (2.4 +/- 1.9 vs 0.9 +/- 0.4, P < .05). CONCLUSIONS: Regional FDG uptake in areas of perfusion defects with stress increased in this group with CAD. These pilot data suggest that stress FDG PET may be diagnostically helpful in obese female patients. This novel approach may complement current methods of CAD detection in women and warrants further study.

Aged↗