Method for transforming CT images for attenuation correction in PET/CT imaging

X-ray computed tomography (CT) imaging plays an essential role in disease diagnosis due to its noninvasive, painless mode and superior penetration depth. However, the resolution of the soft tissue ...

Small-animal positron emission tomography as a tool for neuropharmacology

Our purpose in this study was to compare the impact of contrast material volume in delayed-enhancement computer tomography (CT) imaging for assessing acute reperfused myocardial infarction. In five domestic pigs (20-30 kg), the circumflex coronary artery (CX) was balloon-occluded for 2 h followed by reperfusion. After 5 days, CT imaging was performed after intravenous administration of iodinated contrast material (Iomeprol 400 mgI/ml; Bracco, Italy). A 64-slice multidetector CT (MDCT) (Sensation 64, Siemens) scanner was used for imaging, with standard angiography characteristics. Three scans were performed: first, coronary angiography at first pass with 1.25 gI/kg of contrast material (ART); and remaining delayed-enhancement (DE(1)-DE(2)) 15 min after administration of 1.25 (DE(1)) and 15 min after additional administration of 2.50 gI/kg (=total 3.75 gI/kg - DE(2)). Mean heart rate decreased to 51+/-9 bpm after intravenous administration of Zatebradine (10 mg/kg). Data sets were reconstructed during the end-diastolic phase of the cardiac cycle. Areas of infarction-enhanced (DE), no-reflow (no-reflow) and remote myocardial [remote left ventricle (LV)] were manually contoured. CT attenuation values (Hounsfield units) were measured using five regions of interest: DE, no-reflow, remote LV, left ventricular cavity (lumen LV) and in air. Differences, correlations, signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were calculated. We found significant differences between the attenuation of DE, no-reflow and remote LV (p<0.001). DE and no-reflow size were assessed accurately with DEMDCT. In particular, SNR and CNR showed higher values in DE(2) (approximately 6.0 and 3.5, respectively; r(2)=0.90) vs. DE(1) (approximately 4.0 and 2.2, respectively; r(2)=0.85). The increase of contrast material volume determines a significant improvement in myocardial infarction image quality with DE-MDCT.

To retrospectively determine whether alignment of registered positron emission tomographic (PET) and computed tomographic (CT) data sets obtained independently varies significantly from alignment of data sets acquired from a combined PET/CT scanner. The study was approved by the institution's Human Research Committee with a waiver of informed consent and complied with HIPAA. Whole-body combined PET/CT data sets and separate routinely positioned thoracic CT data sets were obtained from 12 patients (six men, six women; mean age, 48.6 years; range, 24-62 years). Separate PET and thoracic CT data sets matched for patient positioning and respiration were acquired on the same day for nine patients (four men, five women; mean age, 71 years; range, 51-90 years). Computer nonlinear registration was performed on PET and CT data sets from combined PET/CT (fusion group 1), PET data sets from combined PET/CT with unmatched thoracic CT (fusion group 2), and data sets from separate PET and CT matched for patient positioning and respiration (fusion group 3). Quality of alignment was assessed by two radiologists in consensus blinded to the source of registered data in each fusion group at the following anatomic locations: diaphragm, aortic arch, heart, thoracic spine, and lung apices. Results were compared by using the Wilcoxon paired signed rank and unpaired rank sum tests. Quality of alignment did not significantly differ between fusion group 1 and fusion group 3. Fusion group 1 provided significantly better alignment in two of five anatomic locations (P = .008 for diaphragm and P = .031 for heart) than fusion group 2. Fusion group 3 provided significantly better alignment in two of five anatomic locations (P = .037 for diaphragm and P = .009 for heart) than fusion group 2. Thoracic anatomic alignment does not significantly differ between registered PET and CT data sets acquired on a combined PET/CT scanner or from separate PET and CT scanners obtained on the same day when carefully matched for anatomic positioning and respiration.

In recent years, the use of computerized tomography (CT) to characterize two-phase fluid flow through porous media has become increasingly popular. This paper describes a different application of CT: it use as a core analysis tool. The advantages and disadvantages of the different technological generations of commercial medical CT scanners available as core analysis instruments are also discussed. Additionally, methods are presented for improving images and reducing CT-number errors inherent in the scanning of high-density rock samples on instruments whose software was designed for the scanning of the low-density human patients.

Computed tomography (CT) images are used for precise anatomical location of lesions and for accurate attenuation correction in single-photon emission computed tomography (SPECT) image reconstruction in SPECT/CT examination. The aim of this study was to verify the effects of varying CT collimation width and slice thickness on CT images and on CT attenuation corrected SPECT images. We acquired SPECT/CT images of a micro-coin phantom and the National Electrical Manufacturers Association body phantom filled with 99mTc-pertechnetate while varying the abovementioned CT parameters. The full width at half maximum of the slice sensitivity profile, the standard deviation of CT image background noise, and the radiation dose from CT scans were evaluated. Subsequently, the percentage contrast, background variability, and absolute recovery coefficient of the SPECT image were measured. Furthermore, we retrospectively reviewed the clinical bone SPECT images of 23 patients, and statistical testing of differences was performed. As the collimation width and reconstruction slice thickness of the CT image increased, z-axis resolution deteriorated, and background noise decreased. In addition, CT radiation dose decreased with increasing collimation width. Meanwhile, SPECT image quality and quantitative accuracy were unchanged with varying CT collimation width and slice thickness. There were no notable variations in clinical SPECT images and no statistically significant differences. When high-resolution CT slices on the z-axis are not required for clinical diagnosis, increasing collimation width or slice thickness can reduce the radiation dose and image noise with no influence on the quality of SPECT images .

The purpose of the investigation was to assess positron emission tomography (PET), computed tomography (CT) and the image fusion of PET and CT (PET/CT) in the detection of metastases from gastrointestinal neuroendocrine tumors. In a prospective study, thirty-one patients were consecutively examined using a state-of-the-art PET/CT. PET was performed with a carbohydrated F-18-labeled somatostatin receptor ligand (Gluc-Lys([(18)F]FP-TOCA) from the base of the skull to the proximal thigh using a Pico-3D PET scanner. CT was performed with a noncontrast low-dose CT (LD-CT) and a venous-dominant contrast-enhanced CT (VD-CT) from the base of the skull to the proximal thigh and a hepatic arterial-dominant contrast-enhanced CT (AD-CT) from the epigastric region using a 16-slice CT. The data sets from PET and CT (LD-CT and VD-CT) were fused automatically. To assess a relative sensitivity of each imaging modality, the total number of metastases by summing the number of metastases depicted for each patient by the highest sensitive modality was used as reference standard. PET, LD-CT, AD-CT, VD-CT, PET/LD-CT and PET/VD-CT showed a lesion-by-lesion based overall detection rate for liver metastases (n=858) of 90.8% (P<0.001), 29.4% (P<0.001), 45.5% (P<0.001), 73.9% (P<0.001), 91.5% (P<0.001) and 100%. PET, LD-CT, VD-CT, PET/LD-CT and PET/VD-CT showed an overall detection rate for lymph node metastases (n=193) of 93.8% (P<0.001), 25.4% (P<0.001), 64.8% (P<0.001), 93.8% (P<0.001) and 100% and for osseous metastases (n=567) of 98.6% (P<0.005), 40.7% (P<0.001), 40.7% (P<0.001), 100% and 100%. Furthermore, PET revealed 2 (22.2%) of 9 intrapulmonal lesions seen on LD-CT, VD-CT, PET/LD-CT and PET/VD-CT. PET as single modality revealed most liver, lymph node and osseous metastases. The combination of molecular/metabolic with anatomical/morphological information improves the diagnostic accuracy for the detection of metastases in comparison to any single imaging modality. LD-CT cannot replace VD-CT in the detection of liver and lymph node metastases, but was equal in the detection of osseous metastases and identifying of pulmonary lesions.

Background It has become increasingly evident that adipose tissue is a multifunctional organ that produces and secretes various paracrine and endocrine factors. Periadventitial cardiac adipose tissue (PCAT), which exists closely around coronary arteries, is now recognized as a rich source of a number of bioactive molecules. There have been some reports that highlight local chronic inflammation of PCAT as a potential contributing factor to the pathogenesis of coronary artery disease (CAD) and adipose tissue with inflammation is known to have high density in computed tomography (CT). We assessed CT density of adipose tissues to evaluate the inflammatory activity and investigated the association between PCAT inflammation and CAD. Methods and results We assessed the CT density of periadventitial adipose tissues in consecutive 69 patients suspected of CAD ( 51% men, 65 ± 11 years) using 64-slice CT. By using the image scanned for coronary CT angiography, adipose tissue and presence of CAD (&gt;75% organic stenosis) were confirmed in the same scan. We measured CT density of PCAT around the proximal right coronary artery (Coronary-PCAT), pericardial fat apart from coronary arteries (between ascending and descending aorta as the control site; Cont-PCAT), and thoracic subcutaneous fat. In each of these sites, the CT density measurements in two or more regions of interest were randomly performed and the mean value was recorded. The mean of CT density was −81 ± 11 Hounsfield Unit (HU) in Coronary-PCAT, −99±11HU in Cont-PCAT, −103±7HU in the subcutaneous fat, which were significantly different values (p &lt; 0.01). The difference of CT density between Coronary-PCAT and the Cont-PCAT was significantly greater in patients with CAD (n = 30) than those without CAD (n=39) (22±16 versus 16±10 HU, p &lt; 0.05) but the difference between Cont-PCAT and subcutaneous fat was not related to the presence of CAD (6 ± 12 versus 3 ± 14 HU, p = 0.22). Conclusions Coronary-PCAT had significantly higher CT density than the Cont-PCAT and subcutaneous fat. The difference of CT density between Coronary-PCAT and Cont-PCAT was significantly greater in patients with CAD than non-CAD patients. The inflammatory actively of local PCAT rather than whole pericardial fat may implicate in the development of CAD.

BackgroundAccurate kinetic modeling of 18F-fluorodeoxyglucose ([18F]-FDG) positron emission tomography (PET) data requires accurate knowledge of the available tracer concentration in the plasma during the scan time, known as the arterial input function (AIF). The gold standard method to derive the AIF requires collection of serial arterial blood samples, but the introduction of long axial field of view (LAFOV) PET systems enables the use of non-invasive image-derived input functions (IDIFs) from large blood pools such as the aorta without any need for bed movement. However, such protocols require a prolonged dynamic PET acquisition, which is impractical in a busy clinical setting. Population-based input functions (PBIFs) have previously shown potential in accurate Patlak analysis of [18F]-FDG datasets and can enable the use of shortened dynamic imaging protocols. Here, we exploit the high sensitivity and temporal resolution of a LAFOV PET system and explore the use of PBIF with abbreviated protocols in [18F]-FDG total body kinetic modeling.MethodsDynamic PET data were acquired in 24 oncological subjects for 65 min following the administration of [18F]-FDG. IDIFs were extracted from the descending thoracic aorta, and a PBIF was generated from 16 datasets. Five different scaled PBIFs (sPBIFs) were generated by scaling the PBIF with the AUC of IDIF curve tails using various portions of image data (35–65, 40–65, 45–65, 50–65, and 55–65 min post-injection). The sPBIFs were compared with the IDIFs using the AUCs and Patlak Ki estimates in tumor lesions and cerebral gray matter. Patlak plot start time (t*) was also varied to evaluate the performance of shorter acquisitions on the accuracy of Patlak Ki estimates. Patlak Ki estimates with IDIF and t* = 35 min were used as reference, and mean bias and precision (standard deviation of bias) were calculated to assess the relative performance of different sPBIFs. A comparison of parametric images generated using IDIF and sPBIFs was also performed.ResultsThere was no statistically significant difference between AUCs of the IDIF and sPBIFs (Wilcoxon test: P > 0.05). Excellent agreement was shown between Patlak Ki estimates obtained using sPBIF and IDIF. Using the sPBIF55–65 with the Patlak model, 20 min of PET data (i.e., 45 to 65 min post-injection) achieved < 15% precision error in Ki estimates in tumor lesions compared to the estimates with the IDIF. Parametric images reconstructed using the IDIF and sPBIFs with and without an abbreviated protocol were visually comparable. Using Patlak Ki generated with an IDIF and 30 min of PET data as reference, Patlak Ki images generated using sPBIF55–65 with 20 min of PET data (t* = 45 min) provided excellent image quality with structural similarity index measure > 0.99 and peak signal-to-noise ratio > 55 dB.ConclusionWe demonstrate the feasibility of performing accurate [18F]-FDG Patlak analysis using sPBIFs with only 20 min of PET data from a LAFOV PET scanner.

This study aimed to fabricate a heterogeneous phantom replicating the commercial Rando phantom by mixing plaster powder and polylactic acid (PLA) powder. Producing a heterogeneous phantom using Plaster and PLA is cheaper because it can be easily obtained in the commercial market. Additionally, patient-specific Quality Assurance can be easily performed because the phantom can be produced based on the patient’s CT image. PLA has been well studied in the field of radiation therapy and was found to be safe and effective. To match the mean Hounsfield unit (HU) values of the Rando phantom, the bone tissue was changed using plaster and 0–35% PLA powder until an appropriate HU value was obtained, and soft tissue was changed using the PLA infill value until an appropriate HU value was obtained. Bone tissue (200 HU or higher), soft issue (− 500 to 200 HU), and air cavity (less than − 500 HU) were modeled based on the HU values on the computed tomography (CT) image. The bone tissue was modeled as a cavity, and after three-dimensional (3D) printing, a solution containing a mixture of plaster and PLA powder was poured. To evaluate the bone implementation of the phantom obtained by the mixture of plaster and PLA powder, the HU profile of the CT images of the 3D-printed phantom using only PLA and the Rando phantom printed using only PLA was evaluated. The mean HU value for soft tissue in the Rando phantom (− 22.5 HU) showed the greatest similarity to the result obtained with an infill value of 82% (− 20 HU). The mean HU value for bone tissue (669 HU) showed the greatest similarity to the value obtained with 15% PLA powder (680 HU). Thus, for the phantom composed of plaster mixed with PLA powder, soft tissue was fabricated using a 3D printer with an infill value of 82%, and bone tissue was fabricated with a mixture containing 15% PLA powder. In the HU profile, this phantom showed a mean difference of 61 HU for soft tissue and 109 HU for bone tissue in comparison with the Rando phantom. The ratio of PLA powder and plaster can be adjusted to achieve an HU value similar to bone tissue. A simple combination of PLA powder and plaster enabled the creation of a custom phantom that showed similarities to the Rando phantom in both soft tissue and bone tissue.

BackgroundAccurate quantification of radioactivity, measured by an integrated positron emission tomography (PET) and magnetic resonance imaging (MRI) system, is still a challenge. One aspect of such a challenge is to correct for the hardware attenuation, such as the patient table and radio frequency (RF) resonators. For PET/MRI systems, computed tomography (CT) is commonly used to produce hardware attenuation correction (AC) maps, by converting Hounsfield units (HU) to a linear attenuation coefficients (LAC) map at the PET energy level 511 keV, using a bilinear model. The model does not address beam hardening, nor higher density materials, which can lead to inaccurate corrections.PurposeIn this study, we introduce a transmission-based (TX-based) AC technique with a static Germanium-68 (Ge-68) transmission source to generate hardware AC maps using the PET/MRI system itself, without the need for PET or medical CT scanners. The AC TX-based maps were generated for a homogeneous cylinder, made of acrylic as a validator. The technique thereafter was applied to the patient table and posterior part of an RF-phased array used in cardiovascular PET/MRI imaging. The proposed TX-based, and the CT-based, hardware maps were used in reconstructing PET images of one cardiac patient, and the results were analysed and compared.ResultsThe LAC derived by the TX-based method for the acrylic cylinder is estimated to be 0.10851 ± 0.00380 cm−1 compared to the 0.10698 ± 0.00321 cm−1 theoretical value reported in the literature. The PET photon counts were reduced by 8.7 ± 1.1% with the patient table, at the region used in cardiac scans, while the CT-based map, used for correction, over-estimated counts by 4.3 ± 1.3%. Reconstructed in vivo images using TX-based AC hardware maps have shown 4.1 ± 0.9% mean difference compared to those reconstructed images using CT-based AC.ConclusionsThe LAC of the acrylic cylinder measurements using the TX-based technique was in agreement with those in the literature confirming the validity of the technique. The over-estimation of photon counts caused by the CT-based model used for the patient table was improved by the TX-based technique. Therefore, TX-based AC of hardware using the PET/MRI system itself is possible and can produce more accurate images when compared to the CT-based hardware AC in cardiac PET images.

Purpose: To investigate the effect of all user definable CT acquisition parameters on CT numbers for materials of various electron densities, and therefore patient dosimetry. Methods &amp; Materials: CT scanners come supplied with a large number of user definable parameters whose effects on CT numbers are not well documented. An electron density phantom (Gammex RMI 467), with 16 inserts, having 13 densities ranging from 0.28–1.69 g/cm3, was scanned using: helical and axial techniques; 3 kVp settings; 6 reconstruction filter types; 8 mAs settings; 4 different slice thicknesses; and 4 different field of view diameters. In our study we have utilize phantom with 16 inserts. A total of 77 scans were acquired. Results: The most significant variation in CT numbers resulted from the change in kVp settings. CT number variation progressively increases for inserts with density of 1.00 g/cm3 and higher. Standard deviation in CT numbers for 1.69 g/cm3 insert was 8%. However, in a case when kVp held constant adjusting other acquisition parameters (filters, mAs, slice thickness, field of view, technique) resulted in a standard deviation of no more then 3% for all 13 densities. Conclusions: The kVp settings has a most significant effect on CT numbers whereas change in mAs, reconstruction filter type, slice thickness and field of view diameter result in only minor variations. The dosimetric effect for pediatric cases, typically acquired at 90kVp, will be presented.

The correct interpretation of clinical positron emission tomography (PET) data depends largely on the physical limits of the PET scanner. The partial volume effect (PVE) is related to the size of the studied object compared to the spatial resolution. It represents one of the most important limiting factors in quantitative data analysis. This effect is increased in the case of atrophy, as in patients with Alzheimer disease (AD), and it influences measurement of the metabolic reduction generally seen in cerebral degeneration. In this case, interpretation can be biased, because cortical activity will be underestimated due to the atrophy. In general, anatomical images of AD patients have shown diffuse atrophy, while PET studies have found widespread hypometabolism affecting the parietal and temporal lobes. Although hypometabolic areas usually correspond to atrophic regions, they also occur without such changes. Thus, the aim is to differentiate authentic hypometabolism (decrease of glucose consumption per unit volume of gray matter) from that due to PVE from atrophy (cell loss). Consequently, we are using a method for three-dimensional (3D) correction of human PET data with 3D magnetic resonance imaging (MRI). We measured atrophy and metabolism by using both T1-weighted MR images and high and medium resolution PET scans. We injected 12 patients and controls with [18F]fluorodeoxyglucose for glucose consumption measurements. Atrophy was estimated in the following way. We isolated the cerebral structures, using a segmentation technique on the MRI scans, into gray matter (GM), white matter, and cerebrospinal fluid. We superimposed the PET images onto the MR images to obtain anatomo-functional correlations. We degraded the segmented MR images to the resolution of the PET images by a convolution process to create a PET image correction map. We corrected the metabolic PET data for the PVE. We studied the cerebral metabolic rate of glucose in the GM where metabolic variation is the most relevant to AD. By dealing with problems relating to the sensitivity to the segmentation and to the PET-MRI coregistration, computation of MRI convolution processes provided the degree of PVE on a pixel-by-pixel basis, allowing correction of hypometabolisms contained in GM PET values. Global cortical metabolism increased after correction for PVE by, on average, 29 and 24% for tomographs acquired with medium (TTV03 LETI) and high (ECAT 953B CTI/Siemens) resolution, respectively, whereas the cortical metabolism increased by 75 and 65% for the respective tomographs in AD patients. The difference of metabolism between scans after correction for PVE was less than before correction, decreasing from 31 to 17%. This difference was most marked in the frontal and temporal lobes. Fusion imaging allowed correction for PVE in metabolic data using 3D MRI and determination of whether a change in the apparent radiotracer concentration in PET data reflected an alteration in GM volume, a change in radiotracer concentration per unit volume of GM, or both.

Computed tomography (CT) Hounsfield units (HUs) of pathologically confirmed metastatic inguinal lymph nodes (ILNs) were proved to be higher than negative ones. We designed this study to explore the clinical value of CT HU for diagnosing palpable ILN metastasis in patients with penile cancer. A total of 32 patients with penile cancer, including 84 palpable ILNs, were recruited in this study. They all performed 5-mm layer pelvic contrast-enhanced CT (CE-CT) before treatment. The palpable ILNs were matched with CT image. By using radiologic software PACS, the layer with a maximum cross-sectional area of target lymph node was selected, and the short axis was defined as diameter. We outlined the edge of target lymph nodes, and the software automatically calculated its area, maximum CT HU, and average CT HU. All target ILNs were biopsied by surgery to confirm the presence of metastasis. Compared with non-metastatic ILNs, metastatic ILNs had larger diameter, area, maximum non-contrast CT (NC-CT) HU, maximum arterial-phase CE-CT (ACE-CT) HU, average NC-CT HU, and average ACE-CT HU, with statistically significant differences (P < 0.05). Receiver operating characteristic analysis showed the all six parameters (maximum NC-CT HU, maximum ACE-CT HU, average NC-CT HU, average ACE-CT HU, diameter, and area) had significant diagnostic value for ILN metastasis, with an area under the curve of 0.847, 0.853, 0.900, 0.919, 0.809, and 0.789, respectively. The average ACE-CT HU (cutoff: 40.5) had the highest accuracy as 0.857, and maximum NC-CT HU (cutoff: 51.5) had the highest sensitivity of 0.897. ILN CT HU was clinically valuable for the diagnosis of palpable ILN metastasis in patients with newly diagnosed penile cancer.

Technological advances in magnetic resonance imaging (MRI) and computed tomography (CT), including higher spatial and temporal resolution, have made the prospect of performing absolute myocardial perfusion quantification possible, previously only achievable with positron emission tomography (PET). This could facilitate integration of myocardial perfusion biomarkers into the current workup for coronary artery disease (CAD), as MRI and CT systems are more widely available than PET scanners. Cardiac PET scanning remains expensive and is restricted by the requirement of a nearby cyclotron. Clinical evidence is needed to demonstrate that MRI and CT have similar accuracy for myocardial perfusion quantification as PET. However, lack of standardization of acquisition protocols and tracer kinetic model selection complicates comparison between different studies and modalities. The aim of this overview is to provide insight into the different tracer kinetic models for quantitative myocardial perfusion analysis and to address typical implementation issues in MRI and CT. We compare different models based on their theoretical derivations and present the respective consequences for MRI and CT acquisition parameters, highlighting the interplay between tracer kinetic modeling and acquisition settings.