Effects of patient movement on measurements of myocardial blood flow and viability in resting 15O-water PET studies

Background

Patient movement has been considered an important source of errors in cardiac PET. This study was aimed at evaluating the effects of such movement on myocardial blood flow (MBF) and perfusable tissue fraction (PTF) measurements in intravenous ¹⁵O-water PET.

Methods

Nineteen ¹⁵O-water scans were performed on ten healthy volunteers and three patients with severe cardiac dysfunction under resting conditions. Motions of subjects during scans were estimated by monitoring locations of markers on their chests using an optical motion-tracking device. Each sinogram of the dynamic emission frames was corrected for subject motion. Variation of regional MBF and PTF with and without the motion corrections was evaluated.

Results

In nine scans, motions during ¹⁵O-water scan (inter-frame (IF) motion) and misalignments relative to the transmission scan (inter-scan (IS) motion) larger than the spatial resolution of the PET scanner (4.0 mm) were both detected by the optical motion-tracking device. After correction for IF motions, MBF values changed from 0.845 ± 0.366 to 0.780 ± 0.360 mL/minute/g (P < .05). In four scans with only IS motion detected, PTF values changed significantly from 0.465 ± 0.118 to 0.504 ± 0.087 g/mL (P< .05), but no significant change was found in MBF values.

Conclusions

This study demonstrates that IF motion during ¹⁵O-water scan at rest can be source of error in MBF measurement. Furthermore, estimated MBF is less sensitive than PTF values to misalignment between transmission and ¹⁵O-water emission scans.     

Omission of [15O]CO scan for PET CMRO2 examination using 15O-labelled compounds

Objective

CBF, OEF and CMRO₂ provide us important clinical indices and are used for assessing ischemic degree in cerebrovascular disorders. These quantitative images can be measured by PET using ¹⁵O-labelled tracers such as C¹⁵O, C¹⁵O₂ and ¹⁵O₂. To reduce the time of scan, one possibility is to omit the use of CBV data. The present study investigated the influence of fixing the CBV to OEF and CMRO₂ values on subjects with and without cerebrovascular disorders.

Methods

The study consisted of three groups, namely, GROUP-0 (n = 10), GROUP-1 (n = 9), and GROUP-2 (n = 10), corresponding to—without significant disorder, with elevated CBV, and with reduced CBF and elevated OEF, respectively. All subjects received PET examination and using the PET data OEF and CMRO₂ images were computed by fixing CBV and with CBV data. The computed OEF and CMRO₂ values were compared between the methods.

Results

The OEF and CMRO₂ values obtained by fixing the CBV were around 10% underestimation against that with CBV data. The regression analysis showed that these values were comparable (r = 0.93–0.98, P < 0.001). The simulation showed that fixing of the CBV would not derive significant error in either OEF or CMRO₂ values, when changed from 0 to 0.08 ml/g.

Conclusion

This study shows the feasibility of fixing the CBV value for computing OEF and CMRO₂ values in the PET examination, suggesting the CO scan could be eliminated.     

Detection of misery perfusion in the cerebral hemisphere with chronic unilateral major cerebral artery steno-occlusive disease using crossed cerebellar hypoperfusion: comparison of brain SPECT and PET imaging

Purpose

In patients with unilateral internal carotid or middle cerebral artery (ICA or MCA) occlusive disease, the degree of crossed cerebellar hypoperfusion that is evident within a few months after the onset of stroke may reflect cerebral metabolic rate of oxygen in the affected cerebral hemisphere relative to that in the contralateral cerebral hemisphere. The aim of the present study was to determine whether the ratio of blood flow asymmetry in the cerebellar hemisphere to blood flow asymmetry in the cerebral hemisphere on positron emission tomography (PET) and single photon emission computed tomography (SPECT) correlates with oxygen extraction fraction (OEF) asymmetry in the cerebral hemisphere on PET in patients with chronic unilateral ICA or MCA occlusive disease and whether this blood flow ratio on SPECT detects misery perfusion in the affected cerebral hemisphere in such patients.

Methods

Brain blood flow and OEF were assessed using ¹⁵O-PET and N-isopropyl-p-[¹²³I]iodoamphetamine (¹²³I-IMP) SPECT, respectively. All images were anatomically standardized using SPM2. A region of interest (ROI) was automatically placed in the bilateral MCA territories and in the bilateral cerebellar hemispheres using a three-dimensional stereotaxic ROI template, and affected-to-contralateral asymmetry in the MCA territory or contralateral-to-affected asymmetry in the cerebellar hemisphere was calculated. Sixty-three patients with reduced blood flow in the affected cerebral hemisphere on ¹²³I-IMP SPECT were enrolled in this study.

Results

A significant correlation was observed between MCA ROI asymmetry of PET OEF and the ratio of cerebellar hemisphere asymmetry of blood flow to MCA ROI asymmetry of blood flow on PET (r?=?0.381, p?=?0.0019) or SPECT (r?=?0.459, p?=?0.0001). The correlation coefficient was higher when reanalyzed in a subgroup of 43 patients undergoing a PET study within 3 months after the last ischemic event (r?=?0.541, p?=?0.0001 for PET; r?=?0.609, p?<?0.0001 for SPECT). The blood flow ratio on brain perfusion SPECT in all patients provided 100 % sensitivity and 58 % specificity, with 43 % positive and 100 % negative predictive values for detecting abnormally elevated MCA ROI asymmetry of PET OEF.

Conclusion

The ratio of blood flow asymmetry in the cerebellar hemisphere to blood flow asymmetry in the cerebral hemisphere on PET and SPECT correlates with PET OEF asymmetry in the cerebral hemisphere, and this blood flow ratio on SPECT detects misery perfusion in the affected cerebral hemisphere.     

Validation of a simplified scatter correction method for 3D brain PET with <Superscript>15</Superscript>O

Objective

Positron emission tomography (PET) enables quantitative measurements of various biological functions. Accuracy in data acquisition and processing schemes is a prerequisite for this. The correction of scatter is especially important when a 3D PET scanner is used. The aim of this study was to validate the use of a simplified calculation-based scatter correction method for ¹⁵O studies in the brain.

Methods

We applied two scatter correction methods to the same ¹⁵O PET data acquired from patients with cerebrovascular disease (n = 10): a hybrid dual-energy-window scatter correction (reference method), and a deconvolution scatter correction (simplified method). The PET study included three sequential scans for ¹⁵O-CO, ¹⁵O-O₂, and ¹⁵O-H₂O, from which the following quantitative parameters were calculated, cerebral blood flow, cerebral blood volume, cerebral metabolic rate of oxygen, and oxygen extraction fraction.

Results

Both scatter correction methods provided similar reconstruction images with almost identical image noise, although there were slightly greater differences in white-matter regions compared with gray matter regions. These differences were also greater for ¹⁵O-CO than for ¹⁵O-H₂O and ¹⁵O-O₂. Region of interest analysis of the quantitative parameters demonstrated that the differences were less than 10 % (except for cerebral blood volume in white-matter regions), and the agreement between the methods was excellent, with intraclass correlation coefficients above 0.95 for all the parameters.

Conclusions

The deconvolution scatter correction despite its simplified implementation provided similar results to the hybrid dual-energy-window scatter correction. We consider it suitable for application in a clinical ¹⁵O brain study using a 3D PET scanner.

     

Quantification of regional myocardial oxygen metabolism in normal pigs using positron emission tomography with injectable 15O-O2

Purpose

Although ¹⁵O-O₂ gas inhalation can provide a reliable and accurate myocardial metabolic rate for oxygen by PET, the spillover from gas volume in the lung distorts the images. Recently, we developed an injectable method in which blood takes up ¹⁵O-O₂ from an artificial lung, and this made it possible to estimate oxygen metabolism without the inhalation protocol. In the present study, we evaluated the effectiveness of the injectable ¹⁵O-O₂ system in porcine hearts.

Methods

PET scans were performed after bolus injection and continuous infusion of injectable ¹⁵O-O₂ via a shunt between the femoral artery and the vein in normal pigs. The injection method was compared to the inhalation method. The oxygen extraction fraction (OEF) in the lateral walls of the heart was calculated by a compartmental model in view of the spillover and partial volume effect.

Results

A significant decrease of lung radioactivity in PET images was observed compared to the continuous inhalation of ¹⁵O-O₂ gas. Furthermore, the injectable ¹⁵O-O₂ system provides a measurement of OEF in lateral walls of the heart that is similar to the continuous-inhalation method (0.71?±?0.036 and 0.72?±?0.020 for the bolus-injection and continuous-infusion methods, respectively).

Conclusion

These results indicate that injectable ¹⁵O-O₂ has the potential to evaluate myocardial oxygen metabolism.     

Apparent brain temperature imaging with multi-voxel proton magnetic resonance spectroscopy compared with cerebral blood flow and metabolism imaging on positron emission tomography in patients with unilateral chronic major cerebral artery steno-occlusive disease

Purpose

The purpose of the present study was to determine whether apparent brain temperature imaging using multi-voxel proton magnetic resonance (MR) spectroscopy correlates with cerebral blood flow (CBF) and metabolism imaging in the deep white matter of patients with unilateral chronic major cerebral artery steno-occlusive disease.

Methods

Apparent brain temperature and CBF and metabolism imaging were measured using proton MR spectroscopy and ¹⁵O-positron emission tomography (PET), respectively, in 35 patients. A set of regions of interest (ROIs) of 5 × 5 voxels was placed on an MR image so that the voxel row at each edge was located in the deep white matter of the centrum semiovale in each cerebral hemisphere. PET images were co-registered with MR images with these ROIs and were re-sliced automatically using image analysis software.

Results

In 175 voxel pairs located in the deep white matter, the brain temperature difference (affected hemisphere ? contralateral hemisphere: ΔBT) was correlated with cerebral blood volume (CBV) (r = 0.570) and oxygen extraction fraction (OEF) ratios (affected hemisphere/contralateral hemisphere) (r = 0.641). We excluded voxels that contained ischemic lesions or cerebrospinal fluid and calculated the mean values of voxel pairs in each patient. The mean ΔBT was correlated with the mean CBF (r = ? 0.376), mean CBV (r = 0.702), and mean OEF ratio (r = 0.774).

Conclusions

Apparent brain temperature imaging using multi-voxel proton MR spectroscopy was correlated with CBF and metabolism imaging in the deep white matter of patients with unilateral major cerebral artery steno-occlusive disease.

     

PET measurements of CBF,OEF, and CMRO<Subscript>2</Subscript> without arterial sampling in hyperacute ischemic stroke: Method and error analysis

A method for relative measurement of cerebral blood flow (CBF), oxygen extraction fraction (OEF), and metabolic rate of oxygen (CMRO2) using positron emission tomography (PET) without arterial sampling in patients with hyperacute ischemic stroke was presented. METHODS: The method requires two PET scans, one for H2(15)O injection and one for 15O2 inhalation, and calculates regional CBF, CMRO2, and OEF relative to those at the reference brain region by means of table-lookup method. In this study, we calculated "relative lookup-tables" which relate relative CBF to relative H2(15)O count, relative CMRO2 to relative 15O2 count, and relative OEF to relative 15O2/H2(15)O count. Two assumptions were applied to the lookup-table calculation: 1) In the reference region. CBF and OEF were assumed to be 50.0 ml/min/100 ml and 0.40, respectively, 2) Cerebral blood volume (CBV) was assumed to be constant at 4.0 ml/100 ml over the whole brain. Simulation studies were done to estimate the error of the present method derived from the assumptions. RESULTS: For relative CBF measurements, 20% variation in reference CBF gave about +/- 10% error for measured relative CBF at maximum. Changes in CBV caused relatively large errors in measured OEF and CMRO2 when relative CBF and OEF decreased. Errors for measured relative OEF caused by 50% variation in CBV were within +/- 8% at 0.8 of relative CBF and +/- 12% at 0.4 of relative CBF when relative OEF was greater than 1.0. CONCLUSION: CBV effects caused larger errors in estimated OEF and CMRO2 in the region of the ischemic core with decreasing relative CBF and/or OEF but only slight errors in the region of "misery perfusion" with relative OEF values greater than 1.0. The present method makes PET measurements simpler than with the conventional method and increases understanding of the cerebral circulation and oxygen metabolism in patients with hyperacute stroke of several hours after onset.     

Comparison of integrated whole-body [11C]choline PET/MR with PET/CT in patients with prostate cancer

Purpose

To evaluate the performance of conventional [¹¹C]choline PET/CT in comparison to that of simultaneous whole-body PET/MR.

Methods

The study population comprised 32 patients with prostate cancer who underwent a single-injection dual-imaging protocol with PET/CT and subsequent PET/MR. PET/CT scans were performed applying standard clinical protocols (5 min after injection of 793?±?69 MBq [¹¹C]choline, 3 min per bed position, intravenous contrast agent). Subsequently (52?±?15 min after injection) PET/MR was performed (4 min per bed position). PET images were reconstructed iteratively (OSEM 3D), scatter and attenuation correction of emission data and regional allocation of [¹¹C]choline foci were performed using CT data for PET/CT and segmented Dixon MR, T1 and T2 sequences for PET/MR. Image quality of the respective PET scans and PET alignment with the respective morphological imaging modality were compared using a four point scale (0–3). Furthermore, number, location and conspicuity of the detected lesions were evaluated. SUVs for suspicious lesions, lung, liver, spleen, vertebral bone and muscle were compared.

Results

Overall 80 lesions were scored visually in 29 of the 32 patients. There was no significant difference between the two PET scans concerning number or conspicuity of the detected lesions (p not significant). PET/MR with T1 and T2 sequences performed better than PET/CT in anatomical allocation of lesions (2.87?±?0.3 vs. 2.72?±?0.5; p?=?0.005). The quality of PET/CT images (2.97?±?0.2) was better than that of the respective PET scan of the PET/MR (2.69?±?0.5; p?=?0.007). Overall the maximum and mean lesional SUVs exhibited high correlations between PET/CT and PET/MR (ρ?=?0.87 and ρ?=?0.86, respectively; both p?<?0.001).

Conclusion

Despite a substantially later imaging time-point, the performance of simultaneous PET/MR was comparable to that of PET/CT in detecting lesions with increased [¹¹C]choline uptake in patients with prostate cancer. Anatomical allocation of lesions was better with simultaneous PET/MR than with PET/CT, especially in the bone and pelvis. These promising findings suggest that [¹¹C]choline PET/MR might have a diagnostic benefit compared to PET/CT in patients with prostate cancer, and now needs to be further evaluated in prospective trials.     

Significance of chronic marked hyperglycemia on FDG-PET: is it really problematic for clinical oncologic imaging?

Objectives

The purpose of this study was to evaluate the adverse effects of chronic marked hyperglycemia on clinical diagnostic performance of positron emission tomography (PET) using ¹⁸F-fuorodeoxyglucose (FDG).

Methods

Fifty-seven scans of 54 patients, who received FDG-PET for the diagnosis of various cancer(s), and who showed high plasma glucose level of more than 200 mg/dl at the time of administration of FDG in spite of at least 4-h fasting, were retrospectively analyzed. In the clinical follow-up, this high plasma glucose was confirmed as chronic hyperglycemia derived from uncontrolled diabetes (n = 32) and untreated diabetes (n = 25). Based on the final diagnosis of malignancy obtained by histopathology or clinical follow-up for at least 6 months, the diagnostic performance of visual PET analysis was evaluated.

Results

Excluding nine scans of nine patients without sufficient follow-up, final diagnosis was obtained in 48 scans of 45 patients. In 36 scans of 36 patients, at least one malignant lesion was finally confirmed, and true-positive and false-negative results were obtained in 30 and six cases, respectively. Six cases showed false-negative results due to low FDG-avid pathological characteristics (hepatocellular carcinoma, etc.), chemotherapeutic effect or small tumor size. Overall, the patient-based sensitivity, specificity, positive predictive value, negative predictive value and diagnostic accuracy were 83, 83, 94, 63 and 83%, respectively. In lesion-based diagnosis, 56 of 75 lesions (74%) were depicted by PET, while 19 lesions were negative on PET, also due to low FDG-avid characteristics or small size (less than 15 mm).

Conclusions

At the time of chronic hyperglycemia (not acute hyperglycemia), the adverse effect caused by high plasma glucose level was minimum. The FDG uptake of the tumor maintained a sufficiently high level for visual clinical diagnosis in most cases, except in the cases of low FDG-avid tumors or small lesions (15 mm in size).     

The effect of metal artefact reduction on CT-based attenuation correction for PET imaging in the vicinity of metallic hip implants: a phantom study

Background

To determine if metal artefact reduction (MAR) combined with a priori knowledge of prosthesis material composition can be applied to obtain CT-based attenuation maps with sufficient accuracy for quantitative assessment of ¹⁸F-fluorodeoxyglucose uptake in lesions near metallic prostheses.

Methods

A custom hip prosthesis phantom with a lesion-sized cavity filled with 0.2 ml ¹⁸F-FDG solution having an activity of 3.367 MBq adjacent to a prosthesis bore was imaged twice with a chrome–cobalt steel hip prosthesis and a plastic replica, respectively. Scanning was performed on a clinical hybrid PET/CT system equipped with an additional external ¹³⁷Cs transmission source. PET emission images were reconstructed from both phantom configurations with CT-based attenuation correction (CTAC) and with CT-based attenuation correction using MAR (MARCTAC). To compare results with the attenuation-correction method extant prior to the advent of PET/CT, we also carried out attenuation correction with ¹³⁷Cs transmission-based attenuation correction (TXAC). CTAC and MARCTAC images were scaled to attenuation coefficients at 511 keV using a trilinear function that mapped the highest CT values to the prosthesis alloy attenuation coefficient. Accuracy and spatial distribution of the lesion activity was compared between the three reconstruction schemes.

Results

Compared to the reference activity of 3.37 MBq, the estimated activity quantified from the PET image corrected by TXAC was 3.41 MBq. The activity estimated from PET images corrected by MARCTAC was similar in accuracy at 3.32 MBq. CTAC corrected PET images resulted in nearly 40 % overestimation of lesion activity at 4.70 MBq. Comparison of PET images obtained with the plastic and metal prostheses in place showed that CTAC resulted in a marked distortion of the ¹⁸F-FDG distribution within the lesion, whereas application of MARCTAC and TXAC resulted in lesion distributions similar to those observed with the plastic replica.

Conclusions

MAR combined with a trilinear CT number mapping for PET attenuation correction resulted in estimates of lesion activity comparable in accuracy to that obtained with ¹³⁷Cs transmission-based attenuation correction, and far superior to estimates made without attenuation correction or with a standard CT attenuation map. The ability to use CT images for attenuation correction is a potentially important development because it obviates the need for a ¹³⁷Cs transmission source, which entails extra scan time, logistical complexity and expense.     

18F-FDG PET/CT is a valuable tool for relapsing polychondritis diagnose and therapeutic response monitoring

Objectives

To retrospectively investigate the role of ¹⁸ F–fluorodeoxyglucose positron emission tomography/computed tomography (¹⁸F-FDG PET/CT) for the diagnosis and therapeutic response in relapsing polychondritis (RP) patients.

Methods

¹⁸F-FDG PET/CT findings were reviewed in six RP patients. The initial scans were performed for all patients, follow-up scans were performed during steroid therapy for five patients. Changes in the abnormal lesions and the maximal standard uptake value (SUV_max) were analyzed.

Results

The initial PET/CT scans revealed intense FDG uptake in the cartilages for all six patients. The lesions of abnormal FDG uptake were tracheal/bronchial cartilage (n = 4), costicartilage (n = 4), nasal cartilage (n = 3), cricoid cartilage (n = 3), auricular cartilage (n = 3), arytenoid cartilage (n = 3), thyroid cartilage (n = 2), hyoid cartilage (n = 1) and mediastinum lymph node (n = 1). The mean visual score and the mean SUV_max were 2.96 ± 0.20 and 4.10 ± 0.6. The intense uptake reduced or disappeared during steroid therapy for five patients, the mean visual score and the mean SUV_max were 1.58 ± 1.4 and 1.51 ± 1.4.

Conclusions

¹⁸F-FDG PET/CT enables the acquisition of both morphologic and glucose metabolic of the related cartilage structures. It plays a valuable role in assessing almost all cartilage and detecting RP, which is a better selection of a biopsy site as well as therapeutic response monitoring.     

The diagnostic value of 18F-FDG PET and MRI in paediatric histiocytosis

Purpose

To analyse the diagnostic value of ¹⁸F-FDG PET and MRI for the evaluation of active lesions in paediatric Langerhans cell histiocytosis.

Methods

We compared 21 ¹⁸F-FDG PET scans with 21 MRI scans (mean time interval 17 days) in 15 patients (11 male, 4 female, age range 4 months to 19 years) with biopsy-proven histiocytosis. Primary criteria for the lesion-based analysis were signs of vital histiocyte infiltrates (bone marrow oedema and contrast enhancement for MRI; SUV greater than the mean SUV of the right liver lobe for PET). PET and MR images were analysed separately and side-by-side. The results were validated by biopsy or follow-up scans after more than 6 months.

Results

Of 53 lesions evaluated, 13 were confirmed by histology and 40 on follow-up investigations. The sensitivity and specificity of PET were 67 % and 76 % and of MRI were 81 % and 47 %, respectively. MRI showed seven false-positive bone lesions after successful chemotherapy. PET showed five false-negative small bone lesions, one false-negative lesion of the skull and three false-negative findings for intracerebral involvement. PET showed one false-positive lesion in the lymphoid tissue of the head and neck region and two false-positive bone lesions after treatment. Combined PET/MR analysis decreased the number of false-negative findings on primary staging, whereas no advantage over PET alone was seen in terms of false-positive or false-negative results on follow-up.

Conclusion

Our retrospective analysis suggests a pivotal role of ¹⁸F-FDG PET in lesion follow-up due to a lower number of false-positive findings after chemotherapy. MRI showed a higher sensitivity and is indispensable for primary staging, evaluation of brain involvement and biopsy planning. Combined MRI/PET analysis improved sensitivity by decreasing the false-negative rate during primary staging indicating a future role of simultaneous whole-body PET/MRI for primary investigation of paediatric histiocytosis.     

Head motion evaluation and correction for PET scans with 18F-FDG in the Japanese Alzheimer’s disease neuroimaging initiative (J-ADNI) multi-center study

Objective

Head motion during 30-min (six 5-min frames) brain PET scans starting 30 min post-injection of FDG was evaluated together with the effect of post hoc motion correction between frames in J-ADNI multicenter study carried out in 24 PET centers on a total of 172 subjects consisting of 81 normal subjects, 55 mild cognitive impairment (MCI) and 36 mild Alzheimer’s disease (AD) patients.

Methods

Based on the magnitude of the between-frame co-registration parameters, the scans were classified into six levels (A–F) of motion degree. The effect of motion and its correction was evaluated using between-frame variation of the regional FDG uptake values on ROIs placed over cerebral cortical areas.

Result

Although AD patients tended to present larger motion (motion level E or F in 22 % of the subjects) than MCI (3 %) and normal (4 %) subjects, unignorable motion was observed in a small number of subjects in the latter groups as well. The between-frame coefficient of variation (SD/mean) was 0.5 % in the frontal, 0.6 % in the parietal and 1.8 % in the posterior cingulate ROI for the scans of motion level 1. The respective values were 1.5, 1.4, and 3.6 % for the scans of motion level F, but reduced by the motion correction to 0.5, 0.4 and 0.8 %, respectively. The motion correction changed the ROI value for the posterior cingulate cortex by 11.6 % in the case of severest motion.

Conclusion

Substantial head motion occurs in a fraction of subjects in a multicenter setup which includes PET centers lacking sufficient experience in imaging demented patients. A simple frame-by-frame co-registration technique that can be applied to any PET camera model is effective in correcting for motion and improving quantitative capability.

     

Combined correction of recovery effect and motion blur for SUV quantification of solitary pulmonary nodules in FDG PET/CT

Objective

We evaluate a fully data-driven method for the combined recovery and motion blur correction of small solitary pulmonary nodules (SPNs) in F-18 fluorodeoxyglucose (FDG) positron emission tomography (PET)/computed tomography (CT).

Methods

The SPN was segmented in the low-dose CT using a variable Hounsfield threshold and morphological constraints. The combined effect of limited spatial resolution and motion blur in the SPN’s PET image was then modelled by an effective Gaussian point-spread function (psf). Both isotropic and non-isotropic psfs were used. To validate the method, PET/CT measurements of the NEMA/IEC spheres phantom were performed. The method was applied to 50 unselected SPNs ≤30 mm from routine patient care.

Results

Recovery of standardised uptake value (SUV) in the phantom image was significantly improved by combined recovery and motion blur correction compared with recovery-only correction, particularly with the non-isotropic model (residual average error 10%). In the patient images, automated segmentation and fit of the effective psf worked properly in all cases. Volume-equivalent diameter ranged from 4.9 to 27.8 mm. Uncorrected maximum SUV ranged from 0.9 to 13.3. Compared with recovery-only correction, combined correction with the non-isotropic model resulted in a ‘relevant’ (≥30%) SUV increase in 47 SPNs (94%).

Conclusions

Correction of both recovery and motion blur is mandatory for accurate SUV quantification of SPNs.     

Compensation for spill-in and spill-out partial volume effects in cardiac PET imaging

Background

Partial volume effects (PVEs) in PET imaging result in incorrect regional activity estimates due to both spill-out and spill-in from activity in neighboring regions. It is important to compensate for both effects to achieve accurate quantification. In this study, an image-based partial volume compensation (PVC) method was developed and validated for cardiac PET.

Methods and Results

The method uses volume-of-interest (VOI) maps segmented from contrast-enhanced CTA images to compensate for both spill-in and spill-out in each VOI. The PVC method was validated with simulation studies and also applied to images of dog cardiac perfusion PET data. The PV effects resulting from cardiac motion and myocardial uptake defects were investigated and the efficacy of the proposed PVC method in compensating for these effects was evaluated.

Results

Results indicate that the magnitude and the direction of PVEs in cardiac imaging change over time. This affects the accuracy of activity distributions estimates obtained during dynamic studies. The defect regions have different PVEs as compared to the normal myocardium. Cardiac motion contributes around 10% to the PVEs. PVC effectively removed both spill-in and spill-out in cardiac imaging.

Conclusions

PVC improved left ventricular wall uniformity and quantitative accuracy. The best strategy for PVC was to compensate for the PVEs in each cardiac phase independently and treat severe uptake defects as independent regions from the normal myocardium.     

Differential Diagnosis of Patients with Inconclusive Parkinsonian Features Using [18F]FP-CIT PET/CT

Purpose

It is often difficult to differentiate parkinsonism, especially when patients show uncertain parkinsonian features. We investigated the usefulness of dopamine transporter (DAT) imaging for the differential diagnosis of inconclusive parkinsonism using [¹⁸F]FP-CIT PET.

Methods

Twenty-four patients with inconclusive parkinsonian features at initial clinical evaluation and nine healthy controls were studied. Patients consisted of three subgroups: nine patients whose diagnoses were unclear concerning whether they had idiopathic Parkinson’s disease or drug-induced parkinsonism (‘PD/DIP’), nine patients who fulfilled neither the diagnostic criteria of PD nor of essential tremor (‘PD/ET’), and six patients who were alleged to have either PD or atypical parkinsonian syndrome (‘PD/APS’). Brain PET images were obtained 120 min after injection of 185 MBq [¹⁸F]FP-CIT. Imaging results were quantified and compared with follow-up clinical diagnoses.

Results

Overall, 11 of 24 patients demonstrated abnormally decreased DAT availability on the PET scans, whereas 13 were normal. PET results could diagnose PD/DIP and PD/ET patients as having PD in six patients, DIP in seven, and ET in five; however, the diagnoses of all six PD/APS patients remained inconclusive. Among 15 patients who obtained a final follow-up diagnosis, the image-based diagnosis was congruent with the follow-up diagnosis in 11 patients. Four unsolved cases had normal DAT availability, but clinically progressed to PD during the follow-up period.

Conclusion

[¹⁸F]FP-CIT PET imaging is useful in the differential diagnosis of patients with inconclusive parkinsonian features, except in patients who show atypical features or who eventually progress to PD.     

Perfusion CT compared to H<Subscript>2</Subscript><Superscript>15</Superscript>O/O<Superscript>15</Superscript>O PET in patients with chronic cervical carotid artery occlusion

INTRODUCTION: The purpose of this study was to compare the results of perfusion computed tomography (PCT) with those of (15)O(2)/H(2) (15)O positron emission tomography (PET) in a subset of Carotid Occlusion Surgery Study (COSS) patients. MATERIALS AND METHODS: Six patients enrolled in the COSS underwent a standard-of-care PCT in addition to the (15)O(2)/H(2) (15)O PET study used for selection for extracranial-intracranial bypass surgery. PCT and PET studies were coregistered and then processed separately by different radiologists. Relative measurement of cerebral blood flow (CBF) and oxygen extraction fraction (OEF) were calculated from PET. PCT datasets were processed using different arterial input functions (AIF). Relative PCT and PET CBF values from matching regions of interest were compared using linear regression model to determine the most appropriate arterial input function for PCT. Also, PCT measurements using the most accurate AIF were evaluated for linear regression with respect to relative PET OEF values. RESULTS: The most accurate PCT relative CBF maps with respect to the gold standard PET CBF were obtained when CBF values for each arterial territory are calculated using a dedicated AIF for each territory (R (2) = 0.796, p < 0.001). PCT mean transit time (MTT) is the parameter that showed the best correlation with the count-based PET OEF ratios (R (2) = 0.590, p < 0.001). CONCLUSION: PCT relative CBF compares favorably to PET relative CBF in patients with chronic carotid occlusion when processed using a dedicated AIF for each territory. The PCT MTT parameter correlated best with PET relative OEF.     

Influence of residual oxygen-15-labeled carbon monoxide radioactivity on cerebral blood flow and oxygen extraction fraction in a dual-tracer autoradiographic method

Objective  Cerebral blood flow (CBF), cerebral metabolic rate of oxygen (CMRO₂), oxygen extraction fraction (OEF), and cerebral blood volume (CBV) are quantitatively measured with PET with ¹⁵O gases. Kudomi et al. developed a dual tracer autoradiographic (DARG) protocol that enables the duration of a PET study to be shortened by sequentially administrating ¹⁵O₂ and C¹⁵O₂ gases. In this protocol, before the sequential PET scan with ¹⁵O₂ and C¹⁵O₂ gases (¹⁵O₂–C¹⁵O₂ PET scan), a PET scan with C¹⁵O should be preceded to obtain CBV image. C¹⁵O has a high affinity for red blood cells and a very slow washout rate, and residual radioactivity from C¹⁵O might exist during a ¹⁵O₂–C¹⁵O₂ PET scan. As the current DARG method assumes no residual C¹⁵O radioactivity before scanning, we performed computer simulations to evaluate the influence of the residual C¹⁵O radioactivity on the accuracy of measured CBF and OEF values with DARG method and also proposed a subtraction technique to minimize the error due to the residual C¹⁵O radioactivity. Methods  In the simulation, normal and ischemic conditions were considered. The ¹⁵O₂ and C¹⁵O₂ PET count curves with the residual C¹⁵O PET counts were generated by the arterial input function with the residual C¹⁵O radioactivity. The amounts of residual C¹⁵O radioactivity were varied by changing the interval between the C¹⁵O PET scan and ¹⁵O₂–C¹⁵O₂ PET scan, and the absolute inhaled radioactivity of the C¹⁵O gas. Using the simulated input functions and the PET counts, the CBF and OEF were computed by the DARG method. Furthermore, we evaluated a subtraction method that subtracts the influence of the C¹⁵O gas in the input function and PET counts. Results  Our simulations revealed that the CBF and OEF values were underestimated by the residual C¹⁵O radioactivity. The magnitude of this underestimation depended on the amount of C¹⁵O radioactivity and the physiological conditions. This underestimation was corrected by the subtraction method. Conclusions  This study showed the influence of C¹⁵O radioactivity in DARG protocol, and the magnitude of the influence was affected by several factors, such as the radioactivity of C¹⁵O, and the physiological condition.     

Database of normal human cerebral blood flow, cerebral blood volume, cerebral oxygen extraction fraction and cerebral metabolic rate of oxygen measured by positron emission tomography with 15O-labelled carbon dioxide or water, carbon monoxide and oxygen: a multicentre study in Japan

Measurement of cerebral blood flow (CBF), cerebral blood volume (CBV), cerebral oxygen extraction fraction (OEF) and cerebral metabolic rate of oxygen (CMRO₂) by positron emission tomography (PET) with oxygen-15 labelled carbon dioxide (C¹⁵O₂) or ¹⁵O-labelled water (H₂ ¹⁵O), ¹⁵O-labelled carbon monoxide (C¹⁵O) and ¹⁵O-labelled oxygen (¹⁵O₂) is useful for diagnosis and treatment planning in cases of cerebrovascular disease. The measured values theoretically depend on various factors, which may differ between PET centres. This study explored the applicability of a database of ¹⁵O-PET by examining between-centre and within-centre variation in values. Eleven PET centres participated in this multicentre study; seven used the steady-state inhalation method, one used build-up inhalation and three used bolus administration of C¹⁵O₂ (or H₂ ¹⁵O) and ¹⁵O₂. All used C¹⁵O for measurement of CBV. Subjects comprised 70 healthy volunteers (43 men and 27 women; mean age 51.8±15.1 years). Overall mean±SD values for cerebral cortical regions were: CBF=44.4±6.5 ml 100 ml^–1 min^–1; CBV=3.8±0.7 ml 100 ml^–1; OEF=0.44±0.06; CMRO₂=3.3±0.5 ml 100 ml^–1 min^–1. Significant between-centre variation was observed in CBV, OEF and CMRO₂ by one-way analysis of variance. However, the overall inter-individual variation in CBF, CBV, OEF and CMRO₂ was acceptably small. Building a database of normal cerebral haemodynamics obtained by the¹⁵O-PET methods may be practicable.     

Evaluation of a commercial PET tomograph-based system for the quantitative assessment of rCBF,rOEF and rCMRO2 by using sequential administration of 15O-labeled compounds

The purpose of this study was to develop a reliable and practical strategy that generates quantitative CBF and OEF maps accurately from PET data sets obtained with 15O-tracers. Sequential sinogram data sets were acquired after the administration of 15O-tracers, and combined single-frame images were obtained. The delay time between sampled input function and the brain was estimated from the H2(15)O study with the whole brain and the arterial time-activity curves (TACs). The whole-brain TACs were obtained from the reconstructed images (image-base method) and the sinogram data (sinogram-base method). Six methods were also evaluated for the dead-time and decay correction procedures in the process of generating a single-frame image from the dynamic sinogram. The estimated delay values were similar with both the sinogram-based and image-based methods. A lumped correction factor to a previously added single-frame sinogram caused an underestimation of CBF, OEF and CMRO2 by 16% at maximum, as compared with the correction procedure for a short sinogram. This suggested the need for a dynamic acquisition of a sinogram with a short interval. The proposed strategy provided an accurate quantification of CBF and OEF by PET with 15O-tracers.