Design and performance of POSICAM 6.5 BGO positron camera

A high-resolution, whole-body positron camera, POSICAM 6.5 BGO, has been designed, built, and tested; results from it are presented. The camera utilizes 1,320 BGO crystals and 720 PMTS in a staggered geometry to produce high resolution of 5.8 mm FWHM and 21 image planes simultaneously. The axial resolution of the camera is measured at 11.9 mm at the center. High axial sampling is achieved with 5.125 mm separation of the image planes such that three-dimensional imaging of an object can be carried out in a single scan. Recovery of volumetric distribution of radioactivity and object dimensions in axial and sagittal views is demonstrated by imaging spherical objects 13 mm to 39 mm in diameter.     

Implementation of helical computed tomography in magnetic resonance imaging

PURPOSE: To provide a rapid sequence for volumetric imaging of large fields of view. MATERIALS AND METHODS: The volumetric imaging principles of x-ray helical computed tomograpy (CT) were implemented here on an MRI scanner. However, using the advantages offered by MRI, spiral trajectories in K-space were incorporated to make the helical scan more efficient. Thus, data acquisition and interpolations were conducted in K-space and images reconstructed by gridding and applying the inverse Fourier transform. The rapid spiral helical (RASH) imaging method was evaluated by computer simulations, by scanning phantoms and an in vitro heart, and by comparison to conventional multislice interleaved spirals (MSIS) imaging. RESULTS: A significant time saving (61.4% to 85.9%) relative to MSIS was achieved without significant degradation in image quality. Volume assessment and in-plane resolution by RASH were almost identical to the MSIS pulse sequence. The corresponding increase in effective slice width was estimated to range (for the values studied here) from 1.31 to 2.5 according to the selection of the helical pitch and the slice thickness used for imaging. CONCLUSION: The suggested method offers the advantages provided by x-ray helical CT and can be useful in MRI volumetric scanning of large objects.     

Volumetric difference evaluation of registered three-dimensional pre-operative and post-operative CT dental data

Objective: The purpose of this study is to propose a complete methodology for automatically registering three-dimensional (3D) pre-operative and post-operative CT scan dental volumes as well as to provide a toolset for quantifying and evaluating their volumetric differences.Methods: The proposed methodology was applied to cone beam CT (CBCT) data from 20 patients in order to assess the volume of augmented bone in the alveolar region. In each case, the pre-operative and post-operative data were registered using a 3D affine-based scheme. The performance of the 3D registration algorithm was evaluated by measuring the average distance between the edges of the registered sets. The differences between the registered sets were assessed through 3D subtraction radiography. The volume of the differences was finally evaluated by defining regions of interest in each slice of the subtracted 3D data and by combining all respective slices to model the desired volume of interest. The effectiveness of the algorithm was verified by applying it to several reference standard-shaped objects with known volumes.Results: Satisfactory alignment was achieved as a low average offset of 1.483 ± 1.558 mm was recorded between the edges of the registered sets. Moreover, the estimated volumes closely matched the volumes of the reference objects used for verification, as the recorded volume differences were less than 0.4 mm³ in all cases.Conclusion: The proposed method allows for automatic registration of 3D CBCT data sets and the volumetric assessment of their differences in particular areas of interest. The proposed approach provides accurate volumetric measurements in three dimensions, requiring minimal user interaction.     

Improved spectral selectivity and reduced susceptibility in SSFP using a near zero TE undersampled three-dimensional PR sequence

PURPOSE: To improve the performance of fat/water separation and reduce the sensitivity to susceptibility variation in balanced SSFP sequences. MATERIALS AND METHODS: Decreasing the repetition time (TR) reduces susceptibility artifacts in SSFP imaging. A shorter TR may also improve the spectral selectivity obtained when linearly combining data acquired using different radiofrequency phase cycling schedules. The desired short TR is achieved by using an angularly undersampled three-dimensional radial acquisition sequence that achieves a near zero echo time (TE) and also a short TR. RESULTS: Images from human volunteers demonstrate broad coverage of the cervical spine and knee with isotropic resolution. Excellent fat/water separation is achieved in these studies. CONCLUSION: The short TR capability of the proposed sequence greatly improves the fat suppression in SSFP imaging. High-resolution volumetric T2-like contrast imaged with reduced susceptibility artifacts can be obtained from a single acquisition using this technique.     

Segmentation and Feature Extraction Techniques,with Applications to MRI Head Studies

To obtain a three-dimensional reconstruction of the hippocampus from a volumetric MRI head study, it is necessary to separate that structure not only from the surrounding white matter, but also from contiguous areas of gray matter–the amygdala and cerebral cortex. At present it is necessary for a physician to manually segment the hippocampus on each slice of the volume to obtain such a reconstruction. This process is time consuming, and is subject to inter- and intra-operator variation as well as large discontinuities between slices. We propose a novel technique, making use of a combination of gray scale and edge-detection algorithms and some a priori knowledge, by which a computer may make an unsupervised identification of a given structure through a series of contiguous images. This technique is applicable even if the structure includes so-called false contours or missing contours. Applications include three-dimensional reconstruction of difficult-to-segment regions of the brain, and volumetric measurements of structures from series of two-dimensional images.     

Static versus prospective gated non-breath hold volumetric MDCT imaging of the lungs

RATIONALE AND OBJECTIVES: The study's aim is to establish lung-imaging methods that provide for the ability to image the lung under dynamic non-breath hold conditions while providing "virtual breath hold" quantifiable volumetric image data sets. Static breath hold images are used as the gold standard for evaluating these virtual breath hold images in both a phantom and sheep. MATERIALS AND METHODS: Axial methods for gating image acquisition to multiple points in the respiratory cycle interleaved with incremental table stepping during multidetector-row computed tomographic (MDCT) scanning were developed. Data sets are generated over multiple breaths, providing volume images representative of multiple points within a respiratory cycle. To determine the reproducibility and accuracy of the methods, six anesthetized sheep were studied by means of MDCT in nongated and airway-pressure (P(awy))-gated modes in which P(awy) was 0, 7, and 15 cm H2O. RESULTS: No significant differences were found between coefficients of variation in air volume measured from repeated static scans (1.74% +/- 1.78%), gated scans: inspiratory (1.2% +/- 0.44%) or expiratory gated (1.39% +/- 0.98%), or between static (1.74% +/- 1.78%) and gated (1.39% +/- 0.98%) scanning at similar P(awy) (P > .1). Measured air volumes were larger from static versus gated scans by 5.85% +/- 3.77% at 7 cm H2O and 4.45% +/- 3.6% at 15 cm H2O of P(awy) (P < .05), consistent with hysteresis. Differences between air volumes at 7 and 15 cm H2O measured from either static or gated scans or that delivered by a super syringe were insignificant (P < .05). Visual accuracy of three-dimensional anatomic geometry was achieved, and landmark certainty was within 1 mm across respiratory cycles. CONCLUSIONS: A method has been shown that provides for accurate gating to respiratory signals during axial scanning. High-resolution volumetric image data sets are achievable while the scanned subject is breathing. Images are quantitatively similar to breath hold images, with differences likely explained by known pressure-volume hysteresis effects.     

Percutaneous Vertebroplasty: Preliminary Experiences with Rotational Acquisitions and 3D Reconstructions for Therapy Control

Percutaneous vertebroplasty (PVP) is carried out under fluoroscopic control in most centers. The exclusion of implant leakage and the assessment of implant distribution might be difficult to assess based on two-dimensional radiographic projection images only. We evaluated the feasibility of performing a follow-up examination after PVP with rotational acquisitions and volumetric reconstructions in the angio suite. Twenty consecutive patients underwent standard PVP procedures under fluoroscopic control. Immediate postprocedure evaluation of the implant distribution in the angio suite (BV 3000; Philips, The Netherlands) was performed using rotational acquisitions (typical parameters for the image acquisition included a 17-cm field-of-view, 200 acquired images for a total angular range of 180°). Postprocessing of acquired volumetric datasets included multiplanar reconstruction (MPR), maximum intensity projection (MIP), and volume rendering technique (VRT) images that were displayed as two-dimensional slabs or as entire three-dimensional volumes. Image evaluation included lesion and implant assessment with special attention given to implant leakage. Findings from rotational acquisitions were compared to findings from postinterventional CT. The time to perform and to postprocess the rotational acquisitions was in all cases less then 10 min. Assessment of implant distribution after PVP using rotational image acquisition methods and volumetric reconstructions was possible in all patients. Cement distribution and potential leakage sites were visualized best on MIP images presented as slabs. From a total of 33 detected leakages with CT, 30 could be correctly detected by rotational image acquisition. Rotational image acquisitions and volumetric reconstruction methods provided a fast method to control radiographically the result of PVP in our cases.     

Spectrally weighted twisted projection imaging: Reducing T2 signal attenuation effects in fast three-dimensional sodium imaging

A scheme for the reduction of T₂ signal attenuation effects in three-dimensional twisted projection imaging is presented. By purposely reducing the sample density at the high spatial frequencies, a considerable reduction in readout time is achieved. The reduction in readout time leads to decreased T₂ signal attenuation which translates into improved signal-to-noise ratio (SNR). The SNR improvement is achieved without decreasing the image's resolution since the point spread function depends on the sample weighting as well as the T₂ attenuation. The results indicate that SNR improvements of up to 40% can be achieved using the proposed scheme.     

Tissue transition projection (TTP) of the intestines

Tissue transition projection (TTP) represents a three-dimensional reconstruction technique for volumetric image data sets. To demonstrate the principle characteristics of TTP, a simple phantom consisting of two pipes with a simulated, wall-adherent polyp was scanned with spiral CT, and images were reconstructed by means of volume rendering for both opaque surface reconstructions and TTP. Tissue transition projection was used in 7 patients for reconstruction of the small intestine or the colon. Unlike three-dimensional reconstructions with opaque surfaces, TTP enhances surface transitions while suppressing homogeneous areas, allowing delineation of the bowel wall similar to conventional double-contrast studies. Received: 28 July 1999; Accepted: 23 August 1999     

Point vs. volumetric bladder and rectal doses in combined intracavitary-interstitial high-dose-rate brachytherapy: correlation and comparison with published Vienna applicator data

PurposeWe correlated rectal and bladder point and volumetric dose data in patients treated for advanced cervix cancers with combined intracavitary-interstitial high-dose-rate (HDR) brachytherapy (BT). The results are compared with published Vienna applicator data.Methods and MaterialsWe retrospectively analyzed 30 individual combined intracavitary plus interstitial implants from 10 patients treated with external beam radiation therapy (EBRT) followed by HDR BT for locally advanced cervix carcinoma. EBRT consisted of 45 Gy to the pelvis followed by 9–14.4 Gy boost to involved parametria. BT consisted of a total dose of 21 Gy delivered in 7 Gy fraction. For each implant, CT-image-based simulation and image-guided BT treatment planning was performed. Bladder and rectal doses were evaluated and analyzed using both International commission on Radiation Units and Measurements (ICRU) reference points and dose–volume histograms. The cumulative doses to the rectum and bladder were calculated by combining contributions from external beam therapy and BT. To facilitate comparison with published literature, the total doses were normalized to equivalent dose in 2-Gy fractions (EQD₂) using the equation EQD_2total = EQD_2EBRT + EQD_2BT.ResultsFor the patient population considered, the mean ICRU bladder dose was 75 (±4) Gy₃ compared to bladder D_0.1 cc and D_2 cc doses of 84 (±4) and 78 (±3) Gy₃, respectively. The mean ICRU rectal dose was 73 (±4) Gy₃ compared to rectal D_0.1 cc and D_2 cc doses of 79 (±5) and 74 (±4) Gy₃, respectively. For rectum, the mean dose ratios (D_0.1 cc/D_ICRU) and (D_2 cc/D_ICRU) were 1.08 and 1.01, respectively, compared to Vienna applicator study mean dose ratios of 1.08 and 0.93, respectively. ICRU rectal dose correlated with volumetric rectal doses and best with volumetric D_2 cc dose (r_S = 0.91, p = 0.0003); however, ICRU bladder dose did not correlate with volumetric bladder dose.ConclusionsOur study findings reveal a strong correlation between ICRU rectal reference dose and volumetric rectal D_2 cc dose in combined intracavitary-interstitial HDR brachytherapy. This surrogate rectal–dose relationship is valuable in establishing rectal tolerance dose levels in transitioning from traditional two-dimensional to image-based three-dimensional dose planning.     

Simulation of spatial and contrast distortions in keyhole imaging

Keyhole imaging is a scheme introduced to improve temporal resolution in dynamic contrast-enhanced MRI by a factor of four or more. A “full” acquisition before contrast administration is followed by truncated acquisitions sensitive primarily to changes in image contrast. Simulations of the point-spread functions that obtain, and their effect on contrast and spatial resolution, reveal significant degradation only for the smallest objects. Our simulations also address the feasibility of three-dimensional keyhole imaging, and demonstrate a potential 16-fold increase in temporal resolution. This suggests roles for keyhole imaging in conventional (nondynamic) precon-trast and postcontrast studies and other applications.     

Volumetric navigators for prospective motion correction and selective reacquisition in neuroanatomical MRI

We introduce a novel method of prospectively compensating for subject motion in neuroanatomical imaging. Short three-dimensional echo-planar imaging volumetric navigators are embedded in a long three-dimensional sequence, and the resulting image volumes are registered to provide an estimate of the subject's location in the scanner at a cost of less than 500 ms, ~ 1% change in contrast, and ~3% change in intensity. This time fits well into the existing gaps in sequences routinely used for neuroimaging, thus giving a motion-corrected sequence with no extra time required. We also demonstrate motion-driven selective reacquisition of k-space to further compensate for subject motion. We perform multiple validation experiments to evaluate accuracy, navigator impact on tissue intensity/contrast, and the improvement in final output. The complete system operates without adding additional hardware to the scanner and requires no external calibration, making it suitable for high-throughput environments.     

Semi-automated volumetric analysis of artificial lymph nodes in a phantom study

PurposeQuantification of tumour burden in oncology requires accurate and reproducible image evaluation. The current standard is one-dimensional measurement (e.g. RECIST) with inherent disadvantages. Volumetric analysis is discussed as an alternative for therapy monitoring of lung and liver metastases. The aim of this study was to investigate the accuracy of semi-automated volumetric analysis of artificial lymph node metastases in a phantom study.Materials and methodsFifty artificial lymph nodes were produced in a size range from 10 to 55 mm; some of them enhanced using iodine contrast media. All nodules were placed in an artificial chest phantom (artiCHEST^®) within different surrounding tissues. MDCT was performed using different collimations (1–5 mm) at varying reconstruction kernels (B20f, B40f, B60f). Volume and RECIST measurements were performed using Oncology Software (Siemens Healthcare, Forchheim, Germany) and were compared to reference volume and diameter by calculating absolute percentage errors.ResultsThe software performance allowed a robust volumetric analysis in a phantom setting. Unsatisfying segmentation results were frequently found for native nodules within surrounding muscle. The absolute percentage error (APE) for volumetric analysis varied between 0.01 and 225%. No significant differences were seen between different reconstruction kernels. The most unsatisfactory segmentation results occurred in higher slice thickness (4 and 5 mm). Contrast enhanced lymph nodes showed better segmentation results by trend.ConclusionThe semi-automated 3D-volumetric analysis software tool allows a reliable and convenient segmentation of artificial lymph nodes in a phantom setting. Lymph nodes adjacent to tissue of similar density cause segmentation problems. For volumetric analysis of lymph node metastases in clinical routine a slice thickness of ≤3 mm and a medium soft reconstruction kernel (e.g. B40f for Siemens scan systems) may be a suitable compromise for semi-automated volumetric analysis.     

Multiplanar and three-dimensional reconstruction techniques in CT: impact on chest diseases

The purpose of this review is to capture the current state-of-the art of the technical aspects of multiplanar and three-dimensional (3D) images and their thoracic applications. Planimetric and volumetric analysis resulting from volumetric data acquisitions obviates the limitations of segmented transverse images. Among the 3D reconstruction techniques currently available, the most recently introduced technique, i. e., volume rendering, has to be evaluated in comparison with 3D shaded surface display and maximum or minimum intensity projection. Slabs are useful in detecting and localizing micronodular or microtubular patterns and in analyzing mild forms of uneven attenuation of the lungs. Three-dimensional angiography is helpful in the pretherapeutic evaluation and posttreatment follow-up of pulmonary arteriovenous malformations, in the comprehension of the postoperative reorientation of the pulmonary vessels, in the surgical planning of pulmonary tumors, and in the diagnosis of marginated thrombi. The systemic supply to the lung and superior vena cava syndromes are also relevant to these techniques. In acquired or congenital tracheobronchial diseases including stenosis, extraluminal air and complex airway anatomy, multiplanar and 3D reformations have a complementary role to both transaxial images and endoscopy. New developments are also expected in various topics such as 3D conformal radiation therapy, planning of intraluminal bronchoscopic therapy, virtual endoscopy, and functional imaging of the bronchial tree. Miscellaneous clinical applications are promising in the analysis of diaphragmatic morphology and pathophysiology, in the volumetric quantification of the lung parenchyma, and in the vascular components of the thoracic outlet syndromes. Received 5 September 1997; Accepted 8 September 1997     

Comparison of conventional fast spin echo, single-shot two-dimensional and three-dimensional half-fourier RARE for T2-weighted female pelvic imaging

PURPOSE: To evaluate the usefulness of the three-dimensional half-Fourier RARE sequence in comparison with single-shot two-dimensional half-Fourier RARE and conventional fast spin echo (FSE) for female pelvic imaging. MATERIALS AND METHODS: Imaging with all sequences was performed in 146 patients with 166 focal lesions on a 1.5-T system. The images were compared on the basis of quality, lesion conspicuity, and lesion to the uterus contrast-to-noise ratio (CNR). RESULTS: The sharpness of intrapelvic organs on the three-dimensional half-Fourier RARE sequence was better than that on two-dimensional half-Fourier RARE and worse than that on FSE. Motion-related artifacts for three-dimensional half-Fourier RARE were more frequent than those for two-dimensional half-Fourier RARE. There was no statistical difference between the three-dimensional half-Fourier RARE sequence and FSE in regard to lesion conspicuity and overall image quality. The CNR of leiomyoma to myometrium and cervical cancer to cervical stroma was the highest with three-dimensional half-Fourier RARE (P< 0.05). CONCLUSION: The three-dimensional half-Fourier RARE sequence generates images with higher contrast and better image resolution than two-dimensional-RARE. The three-dimensional data set provided images that can be observed in any orientation without acquiring an additional scan by using the multiplanar reconstruction (MPR) method.     

Higher percentage of positive biopsy cores and Gleason score are associated with a greater degree of prostate gland shrinkage after neoadjuvant cytoreductive therapy

PurposeTo determine whether adverse pathologic features, including tumor grade and percent positive biopsy (PPB) cores, predict for prostate size reduction after neoadjuvant cytoreductive therapy.Methods and MaterialsEighty-two consecutive patients who were diagnosed with prostate cancer by transperineal template–guided mapping biopsy (TTMB) received neoadjuvant cytoreductive therapy. The median number of biopsy cores was 59. Thirty patients received a leutinizing hormone–releasing hormone agonist and bicalutamide, whereas 52 patients received bicalutamide (50 mg daily) and dutasteride (0.5 mg daily). A transrectal ultrasound volumetric study of the prostate gland and ellipsoid volume determinations of the prostate gland and transition zone (TZ) were obtained immediately before TTMB and at 90 days (±7 days) after the initiation of neoadjuvant medical therapy. Univariate and multivariate regression analyses were performed to identify predictors of prostate gland and TZ volume reduction.ResultsAt TTMB, the mean prostate volumetric and ellipsoid volumes were 55.4 cm³ and 49.0 cm³, respectively. After neoadjuvant medical therapy, the mean volumetric and ellipsoid prostate volumes were 30.8 cm³ and 28.5 cm³, respectively. On average, the prostate volume decreased by 43.9% and 41.0% on volumetric and ellipsoid measurements, respectively. The TZ volume decreased from 19.8 cm³ to 10.1 cm³ (mean volume reduction of 47.7%). In multivariate analysis, prostate volume cytoreduction was most closely associated with PPB (p = 0.014), TTMB prostate volume (p = 0.01), and drug regimen (p = 0.001).ConclusionsThe degree of prostate volume cytoreduction was positively associated with higher Gleason score and PPBs. Greater reductions in prostate volume may be an indicator of more aggressive cancer.     

In vivo basal ganglia volumetry through application of NURBS models to MR images

Volumetry of basal ganglia (BG) based on magnetic resonance imaging (MRI) provides a sensitive marker in differential diagnosis of BG disorders. The non-uniform rational B-spline (NURBS) surfaces are mathematical representations of three-dimensional structures which have recently been applied in volumetric studies. In this study, a volumetric evaluation of BG based on NURBS was performed in 35 right-handed volunteers. We aimed to compare and validate this technique with respect to manual MRI volumetry and evaluate possible side differences between these structures. Intra- and interobserver biases less than 1.5% demonstrated the method’s stability. The mean percentage differences between NURBS and manual methods were less than 1% for all the structures considered; however, the internal segments of the globus pallidus showed a mean percentage difference of about 1.7%. Rightward asymmetry was found for the caudate nucleus (mean±SD 3.20±0.20 cm³ vs. 3.10±0.19 cm³, P<0.001) for both its head (1.44±0.10 cm³ vs. 1.41±0.09 cm³, P<0.01) and its body/tail (1.73±0.11 cm³ and 1.68±0.12 cm³, P<0.01), and for the globus pallidus (1.23±0.08 cm³ and 1.18±0.09 cm³, P<0.001) for both the internal (0.33±0.05 cm³ vs. 0.31±0.05 cm³, P<0.01) and external (0.90±0.05 cm³ vs. 0.86±0.05 cm³, P<0.001) segments. No volumetric side differences were found for the putamen (3.43±0.14 cm³ vs. 3.39±0.17 cm³, P>0.05). The rightward asymmetry of the BG may be ascribed to the predominant use of the right hand. In conclusion, NURBS is an accurate and reliable method for quantitative volumetry of nervous structures. It offers the advantage of giving a three-dimensional representation of the structures examined.     

Craniosynostosis: diagnostic value of three-dimensional CT reconstruction

Three-dimensional computed tomography (CT) has an important role in determining the presence and extent of congenital and acquired craniofacial deformities. The authors compared the sensitivity and specificity of three-dimensional CT in the detection and characterization of craniosynostosis with that of planar CT and skull radiography. Eighty-two patients with isolated and syndromal synostoses were imaged with CT and three-dimensional CT, and 42 with skull radiography. Three-dimensional CT scan processing was performed by shaded-surface reconstruction, volumetric, and depth-coded methods. Two trained observers read each scan series in a blinded fashion. Diagnostic utility of the images was determined with receiver operating characteristic analysis. The observers ranked three-dimensional shaded images higher than the other types, with three-dimensional volumetric images second and three-dimensional surface images ranked third. Results of this study demonstrate that three-dimensional shaded-surface reconstruction from CT scans is superior to conventional plain radiographs and CT scans in diagnosing craniosynostosis.