Creation of an anthropomorphic CT head phantom for verification of image segmentation.

PURPOSE: Many methods are available to segment structural magnetic resonance (MR) images of the brain into different tissue types. These have generally been developed for research purposes but there is some clinical use in the diagnosis of neurodegenerative diseases such as dementia. The potential exists for computed tomography (CT) segmentation to be used in place of MRI segmentation, but this will require a method to verify the accuracy of CT processing, particularly if algorithms developed for MR are used, as MR has notably greater tissue contrast. METHODS: To investigate these issues we have created a three-dimensional (3D) printed brain with realistic Hounsfield unit (HU) values based on tissue maps segmented directly from an individual T1 MRI scan of a normal subject. Several T1 MRI scans of normal subjects from the ADNI database were segmented using SPM12 and used to create stereolithography files of different tissues for 3D printing. The attenuation properties of several material blends were investigated, and three suitable formulations were used to print an object expected to have realistic geometry and attenuation properties. A skull was simulated by coating the object with plaster of Paris impregnated bandages. Using two CT scanners, the realism of the phantom was assessed by the measurement of HU values, SPM12 segmentation and comparison with the source data used to create the phantom. RESULTS: Realistic relative HU values were measured although a subtraction of 60 was required to obtain equivalence with the expected values (gray matter 32.9-35.8 phantom, 29.9-34.2 literature). Segmentation of images acquired at different kVps/mAs showed excellent agreement with the source data (Dice Similarity Coefficient 0.79 for gray matter). The performance of two scanners with two segmentation methods was compared, with the scanners found to have similar performance and with one segmentation method clearly superior to the other. CONCLUSION: The ability to use 3D printing to create a realistic (in terms of geometry and attenuation properties) head phantom has been demonstrated and used in an initial assessment of CT segmentation accuracy using freely available software developed for MRI.

Technical Note: Development of a 3D printed subresolution sandwich phantom for validation of brain SPECT analysis.

PURPOSE: To make an adaptable, head shaped radionuclide phantom to simulate molecular imaging of the brain using clinical acquisition and reconstruction protocols. This will allow the characterization and correction of scanner characteristics, and improve the accuracy of clinical image analysis, including the application of databases of normal subjects. METHODS: A fused deposition modeling 3D printer was used to create a head shaped phantom made up of transaxial slabs, derived from a simulated MRI dataset. The attenuation of the printed polylactide (PLA), measured by means of the Hounsfield unit on CT scanning, was set to match that of the brain by adjusting the proportion of plastic filament and air (fill ratio). Transmission measurements were made to verify the attenuation of the printed slabs. The radionuclide distribution within the phantom was created by adding (99m)Tc pertechnetate to the ink cartridge of a paper printer and printing images of gray and white matter anatomy, segmented from the same MRI data. The complete subresolution sandwich phantom was assembled from alternate 3D printed slabs and radioactive paper sheets, and then imaged on a dual headed gamma camera to simulate an HMPAO SPECT scan. RESULTS: Reconstructions of phantom scans successfully used automated ellipse fitting to apply attenuation correction. This removed the variability inherent in manual application of attenuation correction and registration inherent in existing cylindrical phantom designs. The resulting images were assessed visually and by count profiles and found to be similar to those from an existing elliptical PMMA phantom. CONCLUSIONS: The authors have demonstrated the ability to create physically realistic HMPAO SPECT simulations using a novel head-shaped 3D printed subresolution sandwich method phantom. The phantom can be used to validate all neurological SPECT imaging applications. A simple modification of the phantom design to use thinner slabs would make it suitable for use in PET.

Lung Parenchymal Assessment in Primary and Secondary Pneumothorax.

RATIONALE: The definition of primary spontaneous pneumothorax excludes patients with known lung disease; however, the assumption that the underlying lung is normal in these patients is increasingly contentious. OBJECTIVES: The purpose of this study was to assess lung structure and compare the extent of emphysema in patients with primary versus secondary spontaneous pneumothorax and to patients with no pneumothorax in an otherwise comparable control group. METHODS: We identified patients treated for pneumothorax by screening inpatient and outpatient medical records at one medical center in the United Kingdom. From this group, 20 patients had no clinically apparent underlying lung disease and were classified as having a primary spontaneous pneumothorax, and 20 patients were classified as having a secondary spontaneous pneumothorax. We assembled a control group composed of 40 subjects matched for age and smoking history who had a unilateral pleural effusion or were suspected to have a thoracic malignancy and had a chest computed tomography scan suitable for quantitative analysis. Demographics and smoking histories were collected. Quantitative evaluation of low-attenuation areas of the lung on computed tomography imaging was performed using semiautomated software, and the extent of emphysema-like destruction was assessed visually. MEASUREMENTS AND MAIN RESULTS: The extent of emphysema and percentage of low-attenuation areas was greater for patients with primary spontaneous pneumothorax than for control subjects matched for age and smoking history (median, 0.25 vs. 0.00%; P = 0.019) and was also higher for patients with secondary pneumothorax than those with primary spontaneous pneumothorax (16.15 vs. 0.25%, P < 0.001). Patients with primary pneumothorax who smoked had significantly greater low-attenuation area than patients with primary pneumothorax who were nonsmokers (0.7 vs. 0.1%, P = 0.034). CONCLUSIONS: The majority of patients with primary spontaneous pneumothorax had quantifiable evidence of parenchymal destruction and emphysema. The exclusion of patients with underlying lung disease from the definition of primary spontaneous pneumothorax should be reappraised.

Comparison of radiation doses from multislice computed tomography coronary angiography and conventional diagnostic angiography.

OBJECTIVES: The aim of this study was to quantify and compare effective doses from conventional angiography and multislice computed tomography (MSCT) coronary angiography using a 16-slice scanner. BACKGROUND: Multislice computed tomography is now a viable modality for cardiac imaging. However, for any diagnostic use of ionizing radiation, the risk to the patient must be considered and justified. METHODS: Multislice computed tomography angiography and conventional angiography were used to assess 180 patients with suspected coronary artery disease. Estimates of effective dose were derived from exposure data recorded for each patient examination. For each modality, a comparable calculation technique was used, based on Monte Carlo modeling of the standard Cristy phantom. RESULTS: In a subset of 91 directly comparable patients the mean effective dose for MSCT coronary angiography was 14.7 mSv (SD 2.2) and that for conventional angiography was 5.6 mSv (SD 3.6). A significant difference in effective dose was seen between the two protocols. CONCLUSIONS: The mean effective dose for MSCT coronary angiography was significantly higher than that for conventional angiography. As MSCT cardiac scanners become increasingly available, operators must be aware of the radiation dose and the factors that affect it.