The efficacy of non-contrast helical computed tomography in the prediction of urinary stone composition in vivo

Can the Hounsfield unit predict the success of medical expulsive therapy using silodosin in 4- to 10-mm distal ureteral stones?

OBJECTIVE

We aimed to investigate the predictive ability of the Hounsfield unit (HU) on non-contrast computed tomography (NCCT) for the success of medical expulsive therapy (MET) using silodosin in distal ureteric stones of 4-10 mm.

METHODOLOGY

The data of patients who underwent MET were retrospectively screened. The patients were divided into two groups as Groups 1 and 2 depending on the presence or absence of stone expulsion, respectively. In addition to HU calculated using the NCCT images, state of the collecting systems, daily fluid intake, number of emergency department visits, and number of pain attacks were compared.

RESULTS

A total of 88 patients were included in the study. Sixty-four patients (72.7%) expelled the stone after MET while the treatment was not successful in 24 patients (27.3%). The stone area was significantly larger in Group 2 (28.4 ± 15.7 mm² vs 46.8 ± 16.1 mm² ; P < .001). NCCT-HU was calculated as 542.5 ± 256.8 for Group 1 and 873.1 ± 335.2 for Group 2, indicating a significant difference (P < .001). The mean number of pain attacks was 1.5 ± 1.2 in Group 1 and 2.2 ± 1.4 in Group 2 (P = .048). The number of visits to the emergency department significantly differed between Groups 1 and 2 (1.1 ± 1.0 and 1.8 ± 1.3, respectively; P = .010).

CONCLUSIONS

In this study, HU and stone area values calculated on NCCT were found to be effective factors in predicting the treatment success for MET. Therefore, we consider that it would be useful to consider these parameters in the selection of an appropriate treatment for distal ureteric stones.

Role of Dual-Energy Computed Tomography in Characterization of Ureteric Calculi and Urinary Obstruction

Objective The present study was carried out to assess the accuracy of dual-energy computed tomography (DECT) in the morphological and chemical characterization of ureteric calculi along with the prediction of the grade of urinary obstruction. Methods This was a prospective observational study that included 100 cases with ultrasonography (USG)-diagnosed ureteric calculi that underwent surgery or had spontaneous expulsion of ureteric calculi. At enrolment, DECT was performed for an in vivo evaluation of volume, chemical composition, and grade of obstruction by subjective assessment of the perinephric edema. After surgical intervention, in vitro evaluation of volume was done by fluid displacement followed by infrared spectroscopy (IRS) for chemical composition. DECT findings were compared with the biochemical analysis and degree of obstruction was validated against excretory CT urograms. Sensitivity, specificity, and the positive predictive and negative predictive values of DECT were assessed. Results No significant difference was observed between the mean volume of stones by fluid displacement (65.1±77.61 mm³) and DECT assessment (66.09±81.78 mm³). IRS revealed the composition of stones as hydroxyapatite, uric acid, cysteine, oxalic acid, and mixed type in 48, 23, 15, five, and nine cases. The sensitivity and specificity of DECT for hydroxyapatite, uric acid, cysteine, oxalic acid, and mixed types were 89.6% and 88.5%, 82.6% and 97.5%, 86.7% and 96.5%, 80% and 98.9%, and 88.9% and 98.9%, respectively. On CT urography, a total of 35 had a high-grade and 65 had a low-grade obstruction, whereas DECT revealed high- and low-grade obstructions in 42 and 58 cases. The sensitivity and specificity of DECT for a high-grade obstruction were 94.3% and 86.2%. Conclusions The findings of the study showed that DECT provides comprehensive information regarding the morphological, chemical, and anatomical characterization of ureteric stones.

The value of X-ray digital tomosynthesis in the diagnosis of urinary calculi

Urinary calculus is a common and recurrent condition that affects kidney function. The present study evaluated the use of digital tomosynthesis (DTS) and Kidneys-Ureters-Bladder (KUB) radiography as methods of diagnosing urinary calculi. Unenhanced multidetector computed tomography (UMDCT) was used in the diagnosis of calculi. KUB radiography and DTS procedures were conducted on patients prior to and following bowel preparation to detect kidney, ureteral and bladder calculi. Differences in diagnostic performance of KUB radiography and DTS imaging on prepared and unprepared bowel were evaluated using the χ² test. The consistency of diagnostic results between two examining physicians was analyzed using the κ test. A total of 138 calculi from 80 patients were detected via UMDCT. The calculi detection rates of KUB prior to and following bowel preparation were 47.8 and 66.7% respectively, and the calculi detection rate of DTS prior to and following bowel preparation were 94.2 and 96.4%, respectively. The detection rates of calculi >5 mm via KUB prior to and following bowel preparation were 56.6 and 73.5% respectively, and in DTS they were 100% prior to and following bowel preparation. Economically, DTS performed on the unprepared bowel was the most cost effective, followed by DTS on the prepared bowel, KUB on the unprepared bowel and KUB on the prepared bowel. Therefore, the current study concluded that DTS may be an appropriate first-line imaging technique in patients with urinary calculi.

Dual-energy computed tomography of canine uroliths

OBJECTIVE To determine whether dual-energy CT (DECT) could accurately differentiate the composition of common canine uroliths in a phantom model. SAMPLE 30 canine uroliths with pure compositions. PROCEDURES Each urolith was composed of ≥ 70% struvite (n = 10), urate (8), cystine (5), calcium oxalate (4), or brushite (3) as determined by standard laboratory methods performed at the Canadian Veterinary Urolith Centre. Uroliths were suspended in an agar phantom, and DECT was performed at low (80 kV) and high (140 kV) energies. The ability of low- and high-energy CT numbers, DECT number, and DECT ratio to distinguish uroliths on the basis of composition was assessed with multivariate ANOVA. RESULTS No single DECT measure differentiated all urolith types. The DECT ratio differentiated urate uroliths from all other types of uroliths. The DECT and low-energy CT numbers were able to differentiate between 8 and 7 pairs of urolith types, respectively. CONCLUSIONS AND CLINICAL RELEVANCE Results indicated that DECT was unable to differentiate common types of canine uroliths in an in vitro model; therefore, it is unlikely to be clinically useful for determining urolith composition in vivo. Given that the primary reasons for determining urolith composition in vivo are to predict response to shock wave lithotripsy and develop a treatment plan, future research should focus on the correlation between DECT measurements and urolith fragility rather than urolith composition.

Combining Mean and Standard Deviation of Hounsfield Unit Measurements from Preoperative CT Allows More Accurate Prediction of Urinary Stone Composition Than Mean Hounsfield Units Alone

INTRODUCTION AND OBJECTIVES

The mineral composition of a urinary stone may influence its surgical and medical treatment. Previous attempts at identifying stone composition based on mean Hounsfield Units (HUm) have had varied success. We aimed to evaluate the additional use of standard deviation of HU (HUsd) to more accurately predict stone composition.

METHODS

We identified patients from two centers who had undergone urinary stone treatment between 2006 and 2013 and had mineral stone analysis and a computed tomography (CT) available. HUm and HUsd of the stones were compared with ANOVA. Receiver operative characteristic analysis with area under the curve (AUC), Youden index, and likelihood ratio calculations were performed.

RESULTS

Data were available for 466 patients. The major components were calcium oxalate monohydrate (COM), uric acid, hydroxyapatite, struvite, brushite, cystine, and CO dihydrate (COD) in 41.4%, 19.3%, 12.4%, 7.5%, 5.8%, 5.4%, and 4.7% of patients, respectively. The HUm of UA and Br was significantly lower and higher than the HUm of any other stone type, respectively. HUm and HUsd were most accurate in predicting uric acid with an AUC of 0.969 and 0.851, respectively. The combined use of HUm and HUsd resulted in increased positive predictive value and higher likelihood ratios for identifying a stone's mineral composition for all stone types but COM.

CONCLUSIONS

To the best of our knowledge, this is the first report of CT data aiding in the prediction of brushite stone composition. Both HUm and HUsd can help predict stone composition and their combined use results in higher likelihood ratios influencing probability.

Relationship between Twinkle Artefacts and in vivo Biochemical Composition of Kidney Stones

INTRODUCTION

Our aim was to predict the chemical composition of kidney stones according to their twinkle artefact (TA) features obtained by in vivo color Doppler ultrasonography and to determine the potential factors affecting the formation and intensity of TAs.

MATERIALS AND METHODS

A total of 101 patients who met the inclusion criteria were included in the study. All patients were evaluated for TAs using color Doppler ultrasonography. All stones were subjected to chemical analysis. The relationships between the TA and the size and chemical composition of the stone, presence of hydronephrosis and body mass index (BMI) were evaluated statistically.

RESULTS

According to the results of the chemical analysis, 66 (65.3%) were calcium oxalate stones. It was found that the in vivo TA intensity did not predict cystine and calcium oxalate monohydrate stones (p > 0.05) and the intensity of TAs increases with increasing BMI (p = 0.002).

CONCLUSION

The present study is the first to show that TAs may not be reliable in overweight patients. The TAs could not predict the chemical composition of stones; so future comprehensive in vivo studies will clarify the role of TAs in the prediction of the stone type preoperatively.

Use of computed tomography scout film and Hounsfield unit of computed tomography scan in predicting the radio-opacity of urinary calculi in plain kidney, ureter and bladder radiographs

Objective:

The objective of this study is to determine the diagnostic utility of computed tomography (CT)- scout film with an optimal non-contrast helical CT scan Hounsfield unit (HU) in predicting the appearance of urinary calculus in the plain kidneys, ureter, urinary bladder (KUB)-radiograph.

Methods:

A prospective cross-sectional study was executed and data were collected from June 2007 to June 2012 at a tertiary hospital. The included subjects were diagnosed to have <10mm urolithiasis with non-contrast helical CT scan and KUB X-ray, which were carried out on the same day. Both KUB radiographs and CT-scout film were read by two qualified radiologists with inter-observer standardization prior to the study. Urolithiasis characteristics such as stone location, CT attenuation value, CT-scout film and KUB radiograph appearance were recorded independently by two observers. Univariate logistic analysis with receiver operating characteristic curve was generated to determine the best cut-off HU value of urolithiases not identified in CT-scout film, but determined radio-opaque in KUB X-ray. Subsequently, its sensitivity, specificity, predictive values and likelihood ratios were calculated. Statistical significance was set at P value of 0.05 or less.

Results:

Two hundred and three valid cases were included. 73 out of 75 CT-scout film detected urolithiasis were identified on plain radiograph and determined as radio-opaque. The determined best cut off value of HU utilized for prediction of radiographic characteristics was 630HU at which urinary calculi were not seen at CT-scout film and were KUB X-ray radio-opaque. The set HU cut-off was established of ideal accuracy with an overall sensitivity of 82.2%, specificity of 96.9% and a positive predictive value of 96.5% and negative predictive value of 83.5%.

Conclusion:

Urolithiases identified on the CT-scout film were also seen as radiopaque on the KUB radiograph while those stones not visible on the CT-scout film, but above the optimal HU cut-off value of 630 are also likely to be radiopaque.

Can the Hounsfield unit predict the success of medically expulsive therapy?

BACKGROUND

We investigate the predictability of medical expulsive therapy (MET) success with alpha blockers based on Hounsfield unit (HU) values and Hounsfield density (HD) values measured by computed tomography (CT) for distal ureteral stones.

METHODS

Between July 2011 and May 2012, 44 patients (19 female and 25 male) with 5- to 10-mm stones in the distal ureters were included in this randomized prospective study. Non-contrast CT examinations were performed in these patients. HU and HD values of stones were calculated. Doxazosine, 4 mg/day orally, was administered as a single dose to all patients for MET.

RESULTS

Patients were divided into 2 groups. Group 1 included 18 patients (43.9%) with dropped stones with MET. Group 2 included 23 patients (56.1%) with no stone passage with MET. In Group 1, the mean stone size was 7.7 mm, the mean HU was 507, and the HD was 53.04/mm. In Group 2, the mean stone size was 8.25 mm, the mean HU was 625, and the mean HD was 61.54/mm. The HU and HD values in Group 2 were higher than in Group 1. However, there was no statistically significant difference (p = 0.85 and 0.93 for HU and HD, respectively).

INTERPRETATION

We found that HU and HD values cannot be used to predict the chances of success for MET. Although the sample size is appropriate for the study, further comparative studies involving more patients are warranted.

Impact of stone density on outcomes in percutaneous nephrolithotomy (PCNL): an analysis of the clinical research office of the endourological society (CROES) pcnl global study database

OBJECTIVE

This study aimed to explore the relationship between stone density and outcomes of percutaneous nephrolithotomy (PCNL) using the Clinical Research Office of the Endourological Society (CROES) PCNL Global Study database.

MATERIAL AND METHODS

Patients undergoing PCNL treatment were assigned to a low stone density [LSD, ≤ 1000 Hounsfield units (HU)] or high stone density (HSD, > 1000 HU) group based on the radiological density of the primary renal stone. Preoperative characteristics and outcomes were compared in the two groups.

RESULTS

Retreatment for residual stones was more frequent in the LSD group. The overall stone-free rate achieved was higher in the HSD group (79.3% vs 74.8%, p = 0.113). By univariate regression analysis, the probability of achieving a stone-free outcome peaked at approximately 1250 HU. Below or above this density resulted in lower treatment success, particularly at very low HU values. With increasing radiological stone density, operating time decreased to a minimum at approximately 1000 HU, then increased with further increase in stone density. Multivariate non-linear regression analysis showed a similar relationship between the probability of a stone-free outcome and stone density. Higher treatment success rates were found with low stone burden, pelvic stone location and use of pneumatic lithotripsy.

CONCLUSIONS

Very low and high stone densities are associated with lower rates of treatment success and longer operating time in PCNL. Preoperative assessment of stone density may help in the selection of treatment modality for patients with renal stones.

Absolute Hounsfield unit measurement on noncontrast computed tomography cannot accurately predict struvite stone composition

BACKGROUND

The purpose of our study was to determine, in vivo, whether single-energy noncontrast computed tomography (NCCT) can accurately predict the presence/percentage of struvite stone composition.

METHODS

We retrospectively searched for all patients with struvite components on stone composition analysis between January 2008 and March 2012. Inclusion criteria were NCCT prior to stone analysis and stone size ≥4 mm. A single urologist, blinded to stone composition, reviewed all NCCT to acquire stone location, dimensions, and Hounsfield unit (HU). HU density (HUD) was calculated by dividing mean HU by the stone's largest transverse diameter. Stone analysis was performed via Fourier transform infrared spectrometry. Independent sample Student's t-test and analysis of variance (ANOVA) were used to compare HU/HUD among groups. Spearman's correlation test was used to determine the correlation between HU and stone size and also HU/HUD to % of each component within the stone. Significance was considered if p<0.05.

RESULTS

Fourty-four patients met the inclusion criteria. Struvite was the most prevalent component with mean percentage of 50.1%±17.7%. Mean HU and HUD were 820.2±357.9 and 67.5±54.9, respectively. Struvite component analysis revealed a nonsignificant positive correlation with HU (R=0.017; p=0.912) and negative with HUD (R=-0.20; p=0.898). Overall, 3 (6.8%) had <20% of struvite component; 11 (25%), 25 (56.8%), and 5 (11.4%) had 21% to 40%, 41% to 60%, and 61% to 80% of struvite, respectively. ANOVA revealed no difference among groups regarding HU (p=0.68) and HUD (p=0.37), with important overlaps. When comparing pure struvite stones (n=5) with other miscellaneous stones (n=39), no difference was found for HU (p=0.09) but HUD was significantly lower for pure stones (27.9±23.6 v 72.5±55.9, respectively; p=0.006). Again, significant overlaps were seen.

CONCLUSIONS

Pure struvite stones have significantly lower HUD than mixed struvite stones, but overlap exists. A low HUD may increase the suspicion for a pure struvite calculus.

Novel evaluation of nephrolithiasis as a complication of gout: a cross-sectional study using helical computerized tomography

PURPOSE

We clarified whether the clinical profiles of patients with a history of urolithiasis (stone formers) truly reflect those of patients who currently have renal stones (stone carriers).

MATERIALS AND METHODS

We evaluated 463 patients with gout using helical computerized tomography, urolithiasis history and relevant clinical parameters.

RESULTS

Nephrolithiasis was observed in 157 of the 463 patients (34%) on helical computerized tomography but only 75 (16%) had a urolithiasis history. Of the 157 stone carriers 107 (68%) did not have a urolithiasis history. In those 157 patients serum urate and serum creatinine were higher than in the 306 nonstone carriers (p = 0.017), and the estimated glomerular filtration rate and urinary pH were lower (p = 0.0096 and 0.0249, respectively). However, there was no significant difference in laboratory findings between the 75 stone formers and 388 nonstone formers. Serum urate and creatinine were higher, and the estimated glomerular filtration rate and urine pH in bilateral stone carriers were lower than in unilateral stone carriers. According to HU density attenuation values on computerized tomography, an estimated third of the calculi that complicated 31 recent gout cases was uric acid.

CONCLUSIONS

The concept of stone formers may lead to underestimating the prevalence of urolithiasis. Our analysis of stone carriers showed that a higher stone burden is associated with greater renal derangement, as determined by serum urate and creatinine, the estimated glomerular filtration rate and urine pH. To accurately clarify the correlation of gout and urolithiasis, it is advantageous to select stone carriers as subjects of study.

Diagnostic utility of attenuation measurement (Hounsfield units) in computed tomography stonogram in predicting the radio-opacity of urinary calculi in plain abdominal radiographs

OBJECTIVE

(1) To determine the best cut-off level of Hounsfield units (HU) in the CT stonogram that would predict the appearance of a urinary calculi in plain KUB X-ray; (2) to estimate the sensitivity and specificity of the best cut-off HU; and (3) to determine whether stone size and location affect the in vivo predictability.

METHODS

A prospective cross-sectional study of patients aged 18-85 diagnosed with urolithiases on CT stonogram with concurrent plain KUB radiograph was conducted. Appearance of stones was recorded, and significant difference between radiolucent and radio-opaque CT attenuation level was determined using ANOVA. Receiver operating characteristics (ROC) curve determined the best HU cut-off value. Stone size and location were used for factor variability analysis.

RESULTS

A total of 184 cases were included in this study, and the average urolithiasis size on CT stonogram was 0.84 cm (0.3-4.9 cm). On KUB X-ray, 34.2 % of the urolithiases were radiolucent and 65.8 % were radio-opaque. Mean value of CT Hounsfield unit for radiolucent stones was 358.25 (±156), and that for radio-opaque stones was 816.51 (±274). ROC curve determined the best cut-off value of HU at 498.5, with the sensitivity of 89.3 % and specificity of 87.3 %. For >4 mm stones, the sensitivity was 91.3 % and the specificity was 81.8 %. On the other hand, for =<4 mm stones, the sensitivity was 60 % and the specificity was 89.5 %.

CONCLUSIONS

Based on the constructed ROC curve, a threshold value of 498.5 HU in CT stonogram was established as cut-off in determining whether a calculus is radio-opaque or radiolucent. The determined overall sensitivity and specificity of the set cut-off HU value are optimal. Stone size but not location affects the sensitivity and specificity.

Genitourinary applications of dual-energy CT

OBJECTIVE

Recent advances in CT technology provide improved diagnostic characterization of materials using dual-energy CT methods. Application of these methods improves lesion conspicuity and detection. In addition, improved material characterization and creation of virtual unenhanced techniques potentially result in decreased radiation dose. We will review the role of dual-energy CT as applied to the genitourinary system.

CONCLUSION

Dual-energy CT is beginning to play an important role in patients with genitourinary diseases by providing unique characterization tools for calculi and masses.

Using Computed Tomography to Predict in Vivo Stone Chemical Composition

Objectives

Several authors hypothesized the usefulness of the non-contrast helical computed tomography (NCHCT) with the determination of stone Hounsfield Unit (HU) values in order to predict urinary stone compositions. Preoperative knowledge of stone composition might be interesting in pre-operative decision-making process. The aim of this study was to evaluate the possible correlation between stone chemical composition and correspondent stone HU value in an in-vivo experience.

Methods

Forty patients with urinary stones were preoperatively studied with abdominal NCHCT, where stone HU values were reported. Stone chemical composition was obtained in each patient, using the colorimetric method. The HU value of each stone was compared with the correspondent chemical analysis.

Results

The median HU values of calcium oxalate (n=10), mixed calcium oxalate and phosphate (n=19), calcium phosphate (n=2), uric acid (n=6) and mixed uric acid and calcium oxalate (n=3) stones were 1060 HU [interquartile range (IQR) 743.75–1222.5]; 900 HU (IQR 588.5–1108.5); 774 HU (range 720–828); 371 HU (IQR 361.25–436.25) and 532 HU (range 476–626), respectively.

Conclusions

Our results confirmed a statistically significant difference of the HU values between calcium and pure uric acid calculi, suggesting a correlation between stone chemical composition and CT-density. Hounsfield unit

Dual source computed tomography: a novel technique to determine stone composition

INTRODUCTION

Dual source computed tomography (CT), a novel technology that employs two different x-ray sources, may provide an image resolution that has not been possible with conventional single source CT. We tested the ability of dual source CT imaging to distinguish calcium oxalate (CaOx) stones from calcium phosphate (CaP) stones, and both types of calciferous stones from uric acid (UA) stones.

METHODS

CaOx, CaP, and UA stones were placed in a tissue phantom and imaged with dual source multidetector CT at both 80kV and 140 kV. Hounsfield units (HU) of each stone were recorded for the 140 kV and the 80 kV datasets by drawing regions of interest by circle, hand-drawing, and using a volume calculation method. The differences between, and the ratios of, the HU obtained by the two energy sources were compared among the stone groups.

RESULTS

Between CaOx and CaP stones, HU differences (80kV-140kV difference, hand-drawing technique: CaOx = 270.7; CaP = 369.5; UA = 11.45; P = 0.020 for CaOx vs. CaP; P < 0.001 for CaOx and CaP vs. UA) as well as ratios (140kV:80kV ratio, hand-drawing technique: CaOx = 1.44; CaP = 1.51; UA = 1.04; P = 0.001 for CaOx vs. CaP; P < 0.001 for CaOx and CaP vs. UA) were significantly different. There were no significant differences in stone size among the groups.

CONCLUSIONS

Dual source CT has the ability to distinguish not only between calciferous stones and uric acid stones, but also among stones composed of different calcium salts. Further studies are warranted to confirm these findings in a clinical setting.

Using Helical CT to Predict Stone Fragility in Shock Wave Lithotripsy (SWL)

Great variability exists in the response of urinary stones to SWL, and this is true even for stones composed of the same mineral. Efforts have been made to predict stone fragility to shock waves using computed tomography (CT) patient images, but most work to date has focused on the use of stone CT number (i.e., Hounsfield units). This is an easy number to measure on a patient stone, but its value depends on a number of factors, including the relationship of the size of the stone to the resolution (i.e., the slicewidth) of the CT scan. Studies that have shown a relationship between stone CT number and failure in SWL are reviewed, and all are shown to suffer from error due to stone size, which was not accounted for in the use of Hounsfield unit values. Preliminary data are then presented for a study of calcium oxalate monohydrate (COM) stones, in which stone structure-rather than simple CT number values-is shown to correlate with fragility to shock waves. COM stones that were observed to have structure by micro CT (e.g., voids, apatite regions, unusual shapes) broke to completion in about half the number of shock waves required for COM stones that were observed to be homogeneous in structure by CT. This result suggests another direction for the use of CT in predicting success of SWL: the use of CT to view stone structure, rather than simply measuring stone CT number. Viewing stone structure by CT requires the use of different viewing windows than those typically used for examining patient scans, but much research to date indicates that stone structure can be observed in the clinical setting. Future clinical studies will need to be done to verify the relationship between stone structure observed by CT and stone fragility in SWL.

[Extra corporeal shock wave lithotripsy (ESWL) procedure in urology]

Since 1980, extra corporeal shock wave lithotripsy (ESWL) has become the first line treatment for most stones in adults and children. The indications are based on criteria depending on localization, chemical composition and size of the renal and ureteral calculi. Since the DORNIER HM 3 which remains the gold standard of first generation lithotripters, many devices of second and third generation have been built (electro hydrolic, piezo electric and electromagnetic) with fluoroscopic and ultrasound localization systems. SWL may now be performed on an out-patient basis without anaesthesia or under neuroleptic analgesia. Indications and evaluation criteria on 3 months plain abdominal X-ray are better defined since 1996. Nevertheless, comparison of reported results remains difficult due to the multiplicity of lithotripter types and the lack of consensus on efficacy criteria. Today, the third generation of mobile electromagnetic lithotripters give an average of 80% stone free rate of patients with kidney and ureteral calculi whatever the localization and size.

Laboratory coherent-scatter analysis of intact urinary stones with crystalline composition: a tomographic approach

Knowledge of urinary stone composition and structure provides important insights in guiding treatment and preventing recurrence. No current method can successfully provide information relating structure and composition of intact stones. We are developing a tomographic technique that uses measures of coherently scattered diagnostic x-rays to yield stone composition. Coherent-scatter (CS) properties depend on molecular structure and are, therefore, sensitive to material composition. Powdered, amorphous or polycrystalline materials with no significant orientation produce circularly symmetric CS patterns. However, in materials with preferred crystallite orientation, like urinary stones, bright spots in CS patterns are observed. This compromises a composition analysis based on comparing CS measurements from calculi to a library of CS signatures from powdered chemicals. We show that a computed tomographic reconstruction of CS measurements using filtered backprojection (CSCT) effectively eliminates bright spots and yields CS patterns equivalent to powdered materials. This allows for direct comparison with a powdered chemical reference library to establish composition. Validation is achieved through a tomographic CS analysis of an aluminium (Al) rod phantom. Much like calculi, CS patterns from a solid polycrystalline Al rod exhibit diffraction spots, absent in the ring-like Al powder CS pattern. We show that the reconstructed Al CS cross-section is equivalent to its powdered counterpart and results in clearly defined composition images. The potential of CSCT to identify stone composition is demonstrated through images of intact stones deemed chemically pure by infrared spectroscopy. Computed tomographic reconstruction of CS signals allowed the generation of composition maps, showing the distribution of stone components. These images provide strong evidence that current laboratory techniques risk missing critical stone components due to inadequate sampling. This is of particular importance since follow-up treatments are based on these composition analyses. CS analysis can distinguish common stone components and can provide topographic composition maps of intact stones. Such details offer invaluable clinical information regarding stone formation, treatment and follow-up, and thus support the development of CS analysis as a laboratory stone analysis technique.

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

OBJECTIVES

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.

METHODS

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.

RESULTS

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).

CONCLUSIONS

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.