Computed Tomography Component Research Articles

XCT analysis of drill cores of Opalinus clay and determination of sample size for effective properties evaluation

In Switzerland, the Opalinus Clay unit was chosen as host rock for a repository for nuclear waste and has recently been investigated in a deep drilling campaign at possible repository construction sites. X-ray images of drill cores were compiled into virtual rock columns and were statistically analyzed with respect to layered compositional variations. This provides insight into scale-dependent homogenization and improves sampling strategy. To predict the repository behavior, using continuum-based models of Opalinus Clay, requires the knowledge of effective properties related to a minimum volume at which Opalinus Clay behaves homogeneously. It turned out that with respect to rock composition, such a volume does not exist in the sense that a single sample of manageable size provides a reliable mean composition. This is because the variation of the cm to dm thick layers, which differ in composition, does not sufficiently homogenize even at the 10-m scale. Thus, effective properties must be obtained by averaging several handleable samples. Regarding the composition of Opalinus Clay at a particular location, about 30 samples, distributed over the whole thickness, with a length of about 30 cm should be measured so that the relative error of the mean value is not higher than 5%–10%. For the statistical analyses computed tomography (CT) values of X-ray data were calibrated with respect to rock composition based on laboratory measurements. The CT values are largely controlled by the respective volume fraction of calcite, quartz, and porous clay matrix. These three components form >80 vol% of the sedimentary rocks studied (also above and below Opalinus Clay). The relationship between CT value and component contents depends on the rock type. The use of data from different rock types to calibrate CT values with respect to composition can lead to erroneous results.

Radiation Dose Assessment for Myocardial Perfusion Imaging: A Single Institution Survey.

This study aims to establish a local diagnostic reference level (LDRL) for single-photon emission tomography/computed tomography (SPECT/CT) and positron emission tomography/CT (PET/CT) with respect to myocardial perfusion imaging (MPI). The acquisition protocol and dosimetry data on the MPI procedures of five SPECT/CT scans and one PET/CT scan were collected. Data on technitum-99m sestamibi (99mTc-sestamibi), 99mTc-tetrofosmin, thallium-201 (201Tl), and rubidium-82 (82RB) were all collected from one centre via questionnaire booklets. Descriptive data analysis was used to analyse all variables, and the 50th percentile was used to analyse each radiation dose quantity. The reported 50th percentile dose for a one-day stress/rest protocol using 99mTc-sestamibi (445/1147 MBq) and 99mTc-tetrofosmin (445/1147 MBq) and for a two-day stress/rest protocol using 99mTc-sestamibi (1165/1184 MBq) and 99mTc-tetrofosmin (1221/1184 MBq) are in good agreement with reported national diagnostic reference levels (NDRLs). However, the dose from the study data on a one-day stress/rest protocol using 99mTc-sestamibi was more than the 50th percentile dose from the Brazilian data (370/1110 MBq) on a similar protocol, and the dose from the study data on a two-day stress/rest protocol using 99mTc-tetrofosmin was more than the 50th percentile dose (1084/1110 MBq) from the United States data on MPI scans. Regarding the computed tomography (CT) portion of the SPECT/CT framework, the 50th percentile doses were lower than all the identified doses in the data considered in the literature reviewed. However, regarding the CT component of the PET/CT MPI scans, the 82RB dose was more than the recorded doses in the CT data in the published literature. This study determined the LDRL of five SPECT/CT protocols and one PET/CT MPI protocol. The results suggest that there may be opportunities to optimise the patient radiation burden from administered activities in patients undergoing SPECT examinations and the CT components associated with 82RB PET/CT scans without compromising diagnostic image quality.

Estimation of radiation dose associated with bone SPECT/CT and establishing local diagnostic reference levels using size-specific dose estimate

Single-photon emission computed tomography (SPECT) and X-ray computed tomography (CT) is used to diagnose and monitor the skeletal system. However, due to the combination of injected activity and CT radiation dose, its usage is linked to an increase in patient radiation exposure. This study aims to estimate the radiation dose received by patients while undergoing bone SPECT/CT and to establish its local diagnostic reference level (LDRL). In this retrospective study, data from 30 patients who had undergone bone scans were obtained from two hospital imaging devices. The effective doses (E) of the radiopharmaceutical agent and CT components were calculated. Furthermore, the patients' anteroposterior thickness at the midline and lateral widths were measured from their CT images to determine the size-specific dose estimate (SSDE). The mean age of the patients was 53.53 ± 16 years. They were administered an injection activity of 740 MBq of 99mTc-Methyl diphosphonate for SPECT, yielding an E of 2.78 mSv. The mean CTDIvol, DLP, SSDE, and E values for the CT component were 8.76 ± 3.25 mGy, 350 ± 138 mGy cm, 13 ± 4 mGy, and 4.90 ± 1.94 mSv, respectively. Patients received a combined dose of 7.68 mSv from the radiopharmaceuticals and CT. The proposed LDRL for SPECT was comparable to international DRLs, but the CT LDRL was slightly higher. An SSDE-based LDRL is proposed. Moreover, the overall patient dose can be reduced even further by optimizing the injected activity and CT imaging factors.

Relative contributions to patient effective dose in SPECT-CT hybrid imaging.

Medical imaging using ionising radiation, while commonplace, has an associated risk of cancer induction. In trying to manage this risk it is beneficial to be able to quantify it through the use of effective dose. Estimates of effective dose resulting from radiopharmaceutical administration are well established in published data but the equivalent data for the computed tomography (CT) component of nuclear medicine hybrid imaging is less well-known. This study aims to estimate the absolute and relative contributions to effective dose from radiopharmaceutical and CT components of common single photon emission computed tomography (SPECT)-CT procedures. Using patient dose-audit data from three SPECT-CT systems we estimated the effective dose resulting from radiopharmaceutical administration by scaling the published effective dose data according to administered activity. The corresponding effective dose resulting from the CT component was estimated using the ImPACT CT dosimetry tool. Absolute effective dose from radiopharmaceutical administrations ranged from 0.2 (Tc-99m colloid head and neck sentinel lymph node imaging) to 14.2 mSv (dual-isotope Tc-99m sestamibi/I-123 sodium iodide parathyroid imaging). Effective dose from the CT components ranged from 0.3 (Tl-201 chloride brain scans - scan range covering the brain) to 4.4 mSv (Tc-99m HYNIC Ty3-Octreotide scans which use a scan range from the top of the brain to bottom of pelvis). Relative contributions (radiopharmaceutical/CT) ranged from 11/89 (Tc-99m colloid head and neck sentinel lymph node imaging) to 98/2% (Tl-201 chloride brain scans). There is a wide range of effective dose from radiopharmaceutical and CT components of hybrid imaging and both aspects can benefit from optimisation efforts, with the largest benefit coming from the CT components.

Factors affecting dose-length product of computed tomography component in whole-body positron emission tomography/computed tomography

In whole-body positron emission tomography (PET)/computed tomography (CT), it is important to optimise the CT radiation dose. We have investigated factors affecting the dose-length product (DLP) of the CT component of whole-body PET/CT and derived equations to predict the DLP. In this retrospective study, 1596 whole-body oncology PET/CT examinations with 18F-fluorodeoxyglucose were analysed. Automatic exposure control was used to modulate radiation dose in CT. Considering age, weight, sex, arm position (up, down, one arm up), scan range (up to the mid-thigh or feet), scan mode (spiral or respiratory-triggered nonspiral) and the presence of a metal prosthesis as potential factors, multivariate analysis was performed to identify independent predictors of DLP and to determine equations to predict DLP. DLP values were predicted using the obtained equations, and compared with actual values. Among body size indices, weight best correlated with DLP in examinations performed under the standard imaging conditions (arms: up; scan range: up to the mid-thigh; scan mode: spiral; and no metal prosthesis). Multivariate analysis indicated that weight, arm position, scan range and scan mode were substantial independent predictors; lowering the arms, extending the scan range and using respiratory-triggered imaging, as well as increasing weight, increased DLP. The degree of the DLP increase tended to increase with increasing weight. The DLP values were predicted using equations that considered these parameters were in excellent agreement with the actual values. The DLP for the CT component of whole-body PET/CT is affected by weight, arm position, scan range and scan mode, and can be predicted with excellent accuracy using these factors.

Sectional Anatomy Quiz - VII.

This series involves a quiz pertaining to the identification of key anatomical landmarks and normal structures present at a given level on the computed tomography (CT) image. The current quiz demonstrates examples of normal and abnormal axial CT images at the level of origin of the coeliac artery. The representative image is subsequently followed by further images demonstrating various commonly encountered pathologies found at this level in clinical practice. In each image, readers are expected to identify highlighted anatomical structures and appreciate how given pathologies can alter the appearance of normal structures. This series aims to advance understanding of sectional anatomy and aid nuclear physicians in the interpretation of the CT component of single photon emission computed tomography (SPECT) and positron emission tomography (PET) studies.

Diagnostic Value of Bone SPECT/CT Using 99mTc-Methylene Diphosphonate in Patients with Unspecified Chest Wall Pain.

We investigated the diagnostic performance of single photon emission computed tomography (SPECT)/computed tomography (CT) as a combination of functional and anatomic imaging, in patients with unspecified chest wall pain. Fifty-two patients with unspecified chest wall pain and no history of recent major traumatic events or cardiac disease were included. The number and location of radioactive chest wall lesions were evaluated on both planar images and SPECT/CT. The clinical diagnosis was made based on all of the clinical and imaging data and follow-up information. Chest wall diseases were diagnosed in 42 patients (80.8 %). SPECT/CT showed abnormal findings in 35 (67.3 %) patients with positive predictive value (PPV) of 97.1 %. SPECT/CT revealed 56 % more lesions than planar bone scan (P = 0.002) and most of the abnormal radioactive lesions (94.6 %) showed combined morphological changes on the matched CT component. When comparing between age subgroups (< 60 y vs. ≥ 60 y), the prevalence of chest wall disease and diagnosis rate of fracture was significantly higher in the older age group. On SPECT/CT, the older age group showed higher frequency of having abnormal finding (95.8 % vs. 42.9 %, P < 0.001) and significantly more lesions were detected (a total of 189 vs. 32, P = 0.003). SPECT/CT showed good diagnostic performance and proved to have higher sensitivity, detecting 56 % more lesions than planar bone scan. A negative result could be helpful for excluding pathologic chest wall disease. SPECT/CT might be recommended for integration in to the diagnostic workup in patients with unspecified chest wall pain, especially in patients ≥ 60 y of age, considering the high disease prevalence and the high frequency of positive results.

CT radiomics-based machine learning classification of atypical cartilaginous tumours and appendicular chondrosarcomas.

BackgroundClinical management ranges from surveillance or curettage to wide resection for atypical to higher-grade cartilaginous tumours, respectively. Our aim was to investigate the performance of computed tomography (CT) radiomics-based machine learning for classification of atypical cartilaginous tumours and higher-grade chondrosarcomas of long bones.MethodsOne-hundred-twenty patients with histology-proven lesions were retrospectively included. The training cohort consisted of 84 CT scans from centre 1 (n=55 G1 or atypical cartilaginous tumours; n=29 G2-G4 chondrosarcomas). The external test cohort consisted of the CT component of 36 positron emission tomography-CT scans from centre 2 (n=16 G1 or atypical cartilaginous tumours; n=20 G2-G4 chondrosarcomas). Bidimensional segmentation was performed on preoperative CT. Radiomic features were extracted. After dimensionality reduction and class balancing in centre 1, the performance of a machine-learning classifier (LogitBoost) was assessed on the training cohort using 10-fold cross-validation and on the external test cohort. In centre 2, its performance was compared with preoperative biopsy and an experienced radiologist using McNemar's test.FindingsThe classifier had 81% (AUC=0.89) and 75% (AUC=0.78) accuracy in identifying the lesions in the training and external test cohorts, respectively. Specifically, its accuracy in classifying atypical cartilaginous tumours and higher-grade chondrosarcomas was 84% and 78% in the training cohort, and 81% and 70% in the external test cohort, respectively. Preoperative biopsy had 64% (AUC=0.66) accuracy (p=0.29). The radiologist had 81% accuracy (p=0.75).InterpretationMachine learning showed good accuracy in classifying atypical and higher-grade cartilaginous tumours of long bones based on preoperative CT radiomic features.FundingESSR Young Researchers Grant.

Assessment of Effective Dose Received in Various Computed Tomography Protocols and Factors Affecting It.

Purpose of Study:The purpose of the study was to evaluate the effect of patient characteristics and equipment-related factors on the computed tomography (CT) dose received by patients from positron emission tomography-CT (PET-CT) using system-generated dose-length product (DLP) values and also to check the effective dose (ED) received from various CT protocols at our institute.Materials and Methods:This retrospective study included 78 adult patients who underwent F-18 fluorodeoxyglucose whole-body PET-CT and were divided into three groups based on the area of primary cancerous lesion. In Group A, we had 44 patients who underwent PET-CT (head-and-neck protocol), in Group B, we had 24 patients who underwent PET-CT (whole body with brain protocol), and in Group C, we had 10 patients who underwent PET-CT (pelvis protocol). All of the patients under the study are of South Asian ethnicity. A majority of patients 53.85% were males and remaining 46.15% were females. The product of conversion factor (k-coefficient), as described in “American Association of Physicists in Medicine Report No. 96” and DLP value generated by the scanner, was used to calculate the ED. Moreover, we also performed regression analysis to check relation between body weight, height, scan range, tube current, Volume computed tomography dose index (CTDIvol), DLP, and ED.Results:The regression analysis shows that scan range, patient height, weight, tube current, and DLP were significantly correlated with ED (P < 0.05 for all). Moreover, the DLP and conversion factor method estimated the ED from various groups. Patients under Group A (head-and-neck protocol), Group B (whole body with brain protocol), Group C (pelvis protocol) received an average ED of 22.45 mSv, 22.40 mSv, and 21.24 mSv, respectively.Conclusion:ED from CT component of PET-CT can be assessed as the product of scanner-generated DLP and conversion factor for selected range. Moreover, body weight, scan range, and tube current had an independent significant effect on ED received from CT.

The Role of Bone Scintigraphy with SPECT/CT in the Characterization and Early Diagnosis of Stage 0 Charcot Neuroarthropathy.

We describe the use of Single Photon Emission Computed Tomography/Computed Tomography (SPECT/CT) in the investigation and diagnosis of Charcot neuroarthropathy (CN) in patients with a hot swollen foot but normal radiographs and clinical suspicion of CN, usually termed Stage 0. This was a retrospective cohort review of 46 diabetes patients who underwent 3 phase bone scintigraphy with “High Resolution” SPECT/CT. The imaging demonstrated that Stage 0 Charcot foot has a distinct bone pathology, which can be classified into three groups: (1) fractures on Computed Tomography (CT) with accompanying focal uptake of tracer on SPECT, (2) bony abnormalities apart from fracture on CT with focal uptake of tracer on SPECT, and (3) normal CT but focal bony uptake of tracer on SPECT. The CT component of SPECT/CT detected bony fractures in 59% of patients. Early treatment with below knee cast and follow-up for 24 months showed only 4 patients who developed Stage 1 Eichenholtz Charcot foot. Our findings support the use of 3 phase bone scintigraphy with SPECT/CT in the characterization and early diagnosis of CN. Stage 0 Charcot foot has a distinct bone pathology which requires urgent treatment to prevent progression to Stage 1 Eichenholtz Charcot foot. If SPECT/CT is unavailable, CT alone will detect bone fracture in 59% patients.

The F-18 FDG PET/CT and CT evaluation of pleural plaques.

Pleural plaques have the possibility of bearing malignancy thus investigation of this entity is important and the most important indicator of malignancy in general is fluorodeoxyglucose (FDG) accumulation in radiological appearance. However there is discrepancy between results of previous studies in the literature about this subject. The aim of this study is to analyze the standardized uptake value of pleural plaques and the cut off levels for malignancy in comparison with computed tomography (CT). Seventy one patients were included in the study (27F, 44M; mean: 59.9 ± 13.1 years). Oncologic F-18 FDG positron emission tomography/computed tomography (PET/CT) was performed to all the subjects for a different primary tumor. Pleural plaques were identified in all patients in CT component of PET/CT examination. Contrast enhanced and nonenhanced CT images were evaluated by a Radiology Physician independently according to the gold standard pathology. The diagnostic sensitivity, specificity of CT was; 39%, 79% respectively and if the cut-off SUVmax level was accepted "4.8" the diagnostic sensitivity and specificity of PET was 71%, and 63% respectively. According to the results and ROC curves determined in the study the cut-off level for evaluation of pleural plaques in PET examination was "4.8". The sensitivity and accuracy of PET was higher compared to CT with this cut-off value.

Sectional Anatomy Quiz IV

In this series we present a quiz about identification of salient and important anatomical landmarks present at a given level on the computed tomography (CT) image. The representative image is followed by further images showing examples of various commonly encountered pathologies that can be seen at this level in clinical practice. Readers are expected to identify highlighted structures in all the images and appreciate how a given abnormality can alter the appearance of normal structures. The aim of this series is to foster understanding and interpretation of the CT component of the single photon emission computed tomography (SPECT) and positron emission tomography (PET) studies help nuclear physicians in interpretation by the nuclear medicine professionals.

P003] Method using radiochromic films to measure the CT dose of female breast during SPECT/CT imaging

Objectives The objective of this work was to test the feasibility of in vivo dosimetry method to be used for the assessment of entrance surface dose (ESD) on female breast from the computed tomography (CT) part of routine clinical SPECT/CT examinations. The difficulty of the problem resides in the fact that the film dosimeter is irradiated both by the radiopharmaceutical and the x-rays from the CT. the proposed method aims to resolve such difficulty. Methods After studying the difference of the films’ energy response between the CT polychromic X-ray radiation and Tc-99 m mono-energetic radiation, and measuring the effect of exposure due to the SPECT part of the exam on the film response; two pieces of XRQA2 films were placed on the patient surface. The first film was withdrawn at the end of the SPECT acquisition time and the second film immediately after the CT scanning part of the examination. The radiation dose from the CT was calculated as the difference between the reflected optical densities from the two films. The in vivo dose measurements were done on 7 patients only due to the rare number of cases when a CT scan is requested by the radiologist in addition to the SPECT study. Results The radiation dose levels on the patients’ skin surface due to the injected radiopharmaceutical were low in magnitude compared with the dose values measured from the CT component of the examination. Results were compared with the scanner registered CTDI(vol). The measured doses were compared with the ones published in the scientific literature. Conclusion The proposed method allows for real patient ESD measurement of the CT component of the SPECT/CT imaging examinations allowing valuable data that can be applied to estimate the radiation dose and risk of exposure to a range of radiosensitive organs such as the gonads, thyroid and the eyes when applicable. The method did not interfere negatively with the image quality of the radiological examination. The technique can be applied easily in the clinical practice when necessary or as part of the annual quality assurance testing of the SPECT/CT imaging system.

Value of 18F-FDG PET/CT imaging in the staging, restaging, monitoring of response to therapy and surveillance of uterine leiomyosarcomas.

Leiomyosarcoma (LMS) is the most common subtype of uterine sarcomas. It is a rare and aggressive tumour. The aim of the present study was to assess the performance of fluorine-18-fluorodeoxyglucose (F-FDG) PET/CT imaging in four clinical settings: initial staging, restaging, monitoring of response to therapy and post-therapy surveillance of uterine LMS. A bicentric retrospective study was carried out on a group of 21 patients with uterine LMS for whom a total of 52 PET/CT scans were available in initial staging (n=11), restaging (n=11), monitoring of response to therapy (n=17) and post-therapy surveillance (n=13). Clinical (minimum 6 months after PET/CT scan) and/or imaging follow-up and pathology were used as the reference standard. In the initial staging, the sensitivity, specificity and accuracy of PET imaging were 80, 100 and 91%, respectively. In the restaging and monitoring of response to therapy, all these indices were 100%, whereas they were lower in post-therapy surveillance at 75, 100 and 85%, respectively, because of two false-negative results. False-negative lesions were an infracentimetric lung nodule in the initial staging and a peritoneal nodule that had increased in size between two PET/CT scans in post-therapy surveillance. PET-negative lesions were all identified on the computed tomography (CT) part of the PET/CT; thus, the performances of the exam improved to 100% on taking into account the CT component of the PET/CT. PET/CT imaging has a high diagnostic yield in the initial staging and restaging of uterine LMS, but seems less sensitive in post-therapy surveillance. Evaluation of the CT part improves the sensitivity of the PET scan. Thus, PET/CT imaging should be considered in patients presenting with LMS.

Optimization of the CT component of SPECT-CT and establishment of local CT diagnostic reference levels for clinical practice.

The aim of this study was to perform a process of optimization and establish local diagnostic reference levels (DRLs) for the computed tomography (CT) component of single-photon emission computed tomography (SPECT)-CT imaging, for use in clinical practice. A multidisciplinary group defined categories for the clinical purpose of the CT component of local SPECT-CT examinations. Each of the examinations were assigned a category, and optimization of acquisition and reconstruction parameters was performed to achieve the required image quality. Dose data were collated for 754 SPECT-CT scans performed on three systems over 10 months. The third quartile values for volume CT dose index and dose length product were calculated and established as local DRLs. Four categories of CT examinations were defined: attenuation correction; localization and attenuation correction; localization, characterization and attenuation correction; and diagnostic and attenuation correction. Local DRLs were established for 11 examinations. Reference was made to the proposed national DRLs set by a recent UK survey. This work describes a process of optimization and the creation of practical and effective local DRLs. These can be used in local audit of practice. In future, improved descriptors and standardization of SPECT-CT use would allow more practicable UK national DRLs to be created.

Sectional Anatomy Quiz.

This image based series comprises of a quiz pertaining to the identification of salient anatomical structures expected to be seen at a given level on the computed tomography (CT) followed by examples of multiple representative pathologies that can be seen at the same level in a routine clinical setting. It is expected that this will improve confidence of nuclear physicians in interpretation of the CT component of the single photon emission computed tomography (SPECT) and positron emission tomography (PET) studies.

Diagnostic accuracy of cadmium-zinc-telluride-based myocardial perfusion SPECT: impact of attenuation correction using a co-registered external computed tomography.

Computed tomography (CT)-based attenuation correction (AC) improves the accuracy of standard myocardial perfusion SPECT. Most dedicated cadmium-zinc-telluride (CZT) SPECT cameras are not equipped with an integrated CT component. We aimed to determine the impact of AC on diagnostic performance of CZT SPECT using co-registration with an external low-dose CT. Sixty patients underwent CZT SPECT (GE Discovery 530c) with (99m)Tc-sestamibi at rest and following regadenoson stress. Using commercial software, SPECT images were co-registered with a low-dose CT acquired on a separate system (GE Discovery 670NMCT). Attenuation corrected and non-corrected (NC) images were reconstructed using an iterative algorithm. Accuracy was measured in 44 patients who had undergone invasive angiography within 6 months. Normalcy was compared in the remaining 16 patients who had a low pre-test likelihood (<5%) of coronary artery disease (CAD). Summed stress and rest scores were significantly lower in AC images (9 ± 8 vs. 13 ± 9 and 6 ± 7 vs. 10 ± 9, P = 0.01), while summed difference score did not differ. According to angiography, 38 patients had significant CAD in 71 vascular territories. Attenuation correction improved accuracy globally (P = 0.03) and in RCA territory (P = 0.008). Specificity improved both globally (100 vs. 40%, P < 0.05) and in each individual territory (LAD: 63 vs. 36%, LCX: 70 vs. 33%, RCA: 81 vs. 19%, P < 0.01). Normalcy was 100% for AC and 62.5% for NC images (P < 0.05). Attenuation correction with a co-registered external CT is feasible using CZT cameras and improves diagnostic accuracy mostly by improving specificity over uncorrected images.

A method for accurate spatial registration of PET images and histopathology slices.

BackgroundAccurate alignment between histopathology slices and positron emission tomography (PET) images is important for radiopharmaceutical validation studies. Limited data is available on the registration accuracy that can be achieved between PET and histopathology slices acquired under routine pathology conditions where slices may be non-parallel, non-contiguously cut and of standard block size. The purpose of this study was to demonstrate a method for aligning PET images and histopathology slices acquired from patients with laryngeal cancer and to assess the registration accuracy obtained under these conditions.MethodsSix subjects with laryngeal cancer underwent a 64Cu-copper-II-diacetyl-bis(N4-methylthiosemicarbazone) (64Cu-ATSM) PET computed tomography (CT) scan prior to total laryngectomy. Sea urchin spines were inserted into the pathology specimen to act as fiducial markers. The specimen was fixed in formalin, as per standard histopathology operating procedures, and was then CT scanned and cut into millimetre-thick tissue slices. A subset of the tissue slices that included both tumour and fiducial markers was taken and embedded in paraffin blocks. Subsequently, microtome sectioning and haematoxylin and eosin staining were performed to produce 5-μm-thick tissue sections for microscopic digitisation. A series of rigid registration procedures was performed between the different imaging modalities (PET; in vivo CT—i.e. the CT component of the PET-CT; ex vivo CT; histology slices) with the ex vivo CT serving as the reference image. In vivo and ex vivo CTs were registered using landmark-based registration. Histopathology and ex vivo CT images were aligned using the sea urchin spines with additional anatomical landmarks where available. Registration errors were estimated using a leave-one-out strategy for in vivo to ex vivo CT and were estimated from the RMS landmark accuracy for histopathology to ex vivo CT.ResultsThe mean ± SD accuracy for registration of the in vivo to ex vivo CT images was 2.66 ± 0.66 mm, and the accuracy for registration of histopathology to ex vivo CT was 0.86 ± 0.41 mm. Estimating the PET to in vivo CT registration accuracy to equal the PET-CT alignment accuracy of 1 mm resulted in an overall average registration error between PET and histopathology slices of 3.0 ± 0.7 mm.ConclusionsWe have developed a registration method to align PET images and histopathology slices with an accuracy comparable to the spatial resolution of the PET images.

Cardiac PET for translational imaging.

All along, translational cardiovascular research has been dependent on non-invasive imaging (such as single-photon emission computed tomography (SPECT), positron emission tomography (PET), computed tomography (CT), echocardiography, or magnetic resonance imaging (MRI)), as these techniques allow the assessment of surrogate markers in intact living organisms non-invasively. PET offers the advantages of high sensitivity; the capability for longitudinal, quantitative imaging; and that an armamentarium of promising radiotracers is readily available. All commercially available PET scanners are equipped with a CT component, and thus, the often cited disadvantage of a lack of morphologic correlation does not really count anymore. This review aims to give an outline on PET as a promising tool for translational research in cardiology as dedicated preclinical systems with virtually the same imaging features as those used in clinical imaging allows the straightforward concept of "bench to bedside."

Patient doses from hybrid SPECT-CT procedures.

The aim of this work is to estimate patient doses from hybrid single-photon emission computed tomography (SPECT) and computed tomography (CT) procedures. The study involved all four SPECT-CT systems in Bulgaria. Effective dose was estimated for about 100 patients per system. Ten types of examinations were considered, representing all diagnostic procedures performed in the SPECT-CT systems. Effective doses from the SPECT component were calculated applying the ICRP 53 and ICRP 80 conversion coefficients. Computed tomography dose index and dose length product were retrospectively obtained from the archives of the systems, and effective doses from the CT component were calculated with CT-Expo software. Parallel estimation of CT component contribution with the National Radiological Protection Board (NRPB) conversion coefficients was performed where applicable. Large variations were found in the current practice of SPECT-CT imaging. Optimisation actions and diagnostic reference levels were proposed.