Helical computed tomography accurately reports urinary stone composition using attenuation values: in vitro verification using high-resolution micro-computed tomography calibrated to fourier transform infrared microspectroscopy.
ABSTRACT To assess the ability of helical computed tomography (CT) to differentiate regions of known mineral composition in typical, heterogeneous urinary stones. Interest is substantial in the urologic community in using radiologic imaging to determine accurately the composition of urinary calculi. Recent advances in CT make this a viable prospect, but the heterogeneity of most stones is a complicating factor.
The ability of micro-CT (a high-resolution laboratory instrument) to identify the mineral composition of stones was confirmed by calibrating micro-CT attenuation values to pure mineral regions of sliced stones using infrared microspectroscopy. Intact human urinary stones were then analyzed by micro-CT, and regions-of-interest of pure mineral were correlated with identical regions-of-interest from quad slice multi-detector row helical CT images. With helical CT, narrow slice widths were used to decrease volume-averaging errors, and bone windows were used so that internal stone structure was visible.
When stones were imaged using helical CT at narrow slice widths, mineral-specific regions-of-interest yielded nonoverlapping attenuation values for uric acid (566 to 632 Hounsfield units [HU]), struvite (862 to 944 HU), calcium oxalate (1416 to 1938 HU), and hydroxyapatite (2150 to 2461 HU).
High resolution helical CT yields unique attenuation values for common types of stone mineral, but proper windowing is required to localize regions of homogeneity. The results of this in vitro study suggest that high-resolution helical CT may be able to identify stone composition at patient diagnosis.
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ABSTRACT: Nasopharyngeal tonsilloliths are less well known to radiologists than palatine tonsil lithiases. The possibility of routinely available fine slices during CT scans of the head and neck prompted a retrospective study on the causes and radiological signs and patterns of nasopharyngeal tonsilloliths. A total of 515 CT scans were retrospectively re-examined looking for calcifications of the posterior wall of the nasopharynx. One patient with this type of calcification underwent a cerebral MRI as part of the etiological workup of his faintness, which also provided a study of the nasopharyngeal wall. The size, density, and position of these calcium concretions were analyzed with CT in all cases. In 31 patients (18 men, 13 women), we discovered one or several calcifications in the pharyngeal mucous area, between 2 and 5.5 mm in size, with a median density of 202 HU. In two cases, we observed that these calcifications adhered to an adenoid cyst, whereas in three cases, the patients had both palatine tonsil and nasopharyngeal calcifications. None of the 31 patients had previously had an adenoidectomy. Sagittal CT and MRI images clearly localized all these calcifications before the pharyngobasilar fascia. The position of these nasopharyngeal calcifications in front of the pharyngobasilar fascia means that a calcified vestige of the notochord can be ruled out. Moreover, the simultaneous presence of nasopharyngeal tonsil and palatine tonsil calcifications in three patients is an additional argument for considering these calcifications of the posterior wall of the nasopharynx as tonsilloliths, all of which, representing 6% of the CTs in our series, were asymptomatic. The nasopharyngeal tonsilloliths are stones less than 1 cm in size lodged in the pharyngeal tonsils that are frequently detected on CT when there are no clinical symptoms.Journal de Radiologie 03/2007; 88(2):259-62. · 0.42 Impact Factor
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ABSTRACT: Micro computed tomography (micro CT) has been shown to provide exceptionally high quality imaging of the fine structural detail within urinary calculi. We tested the idea that micro CT might also be used to identify the mineral composition of urinary stones non-destructively. Micro CT x-ray attenuation values were measured for mineral that was positively identified by infrared microspectroscopy (FT-IR). To do this, human urinary stones were sectioned with a diamond wire saw. The cut surface was explored by FT-IR and regions of pure mineral were evaluated by micro CT to correlate x-ray attenuation values with mineral content. Additionally, intact stones were imaged with micro CT to visualize internal morphology and map the distribution of specific mineral components in 3-D. Micro CT images taken just beneath the cut surface of urinary stones showed excellent resolution of structural detail that could be correlated with structure visible in the optical image mode of FT-IR. Regions of pure mineral were not difficult to find by FT-IR for most stones and such regions could be localized on micro CT images of the cut surface. This was not true, however, for two brushite stones tested; in these, brushite was closely intermixed with calcium oxalate. Micro CT x-ray attenuation values were collected for six minerals that could be found in regions that appeared to be pure, including uric acid (3515 - 4995 micro CT attenuation units, AU), struvite (7242 - 7969 AU), cystine (8619 - 9921 AU), calcium oxalate dihydrate (13815 - 15797 AU), calcium oxalate monohydrate (16297 - 18449 AU), and hydroxyapatite (21144 - 23121 AU). These AU values did not overlap. Analysis of intact stones showed excellent resolution of structural detail and could discriminate multiple mineral types within heterogeneous stones. Micro CT gives excellent structural detail of urinary stones, and these results demonstrate the feasibility of identifying and localizing most of the common mineral types found in urinary calculi using laboratory CT.BMC Urology 01/2005; 4(1):15. · 1.45 Impact Factor