Can contrast-enhanced ultrasonography characterize focal liver lesions and differentiate between benign and malignant, thus providing a one-stop imaging service for patients?()

PURPOSE

Contrast-enhanced ultrasonography (CEUS) displays high sensitivity and specificity in characterizing focal liver lesions (FLLs). We attempted to determine how often CEUS provides an unequivocal diagnosis of FLLs that does not require additional imaging studies.

MATERIALS AND METHODS

Seventy-three patients with 146 FLLs were scanned with B-mode, Doppler, and contrast-enhanced US (2 × 2.4 ml SonoVue, low MI, 4-6 MHz curved array transducer, Toshiba Aplio/Siemens-Acuson Sequoia). Data were digitally stored and transferred to a work station with the GE PACS system. Images were reviewed by a consultant radiologist experienced in CEUS and interpreted in accordance with the criteria for characterizing FLLs published by the European Federation of Societies for Ultrasound in Medicine and Biology. Diagnoses were compared with those based on computed tomography (CT) and/or magnetic resonance (MR) findings if these were available. However, our aim was to assess the frequency with which CEUS provided diagnoses that were considered reliable enough to exclude the need for other imaging studies. Therefore, the CEUS diagnoses were not necessarily confirmed by other methods.

RESULTS

Based on CEUS findings alone, 130/146 (89.0%) FLLs could be classified as benign or malignant, and in 118/146 (80.8%) cases, the lesion could be specifically identified. The other 28/146 (19.2%) FLLs could not be characterized based on CEUS data alone. In 58 (80.8%) of the 73 patients with multiple FLLs, CEUS findings were sufficient to establish the benign vs. malignant nature of all the patient's lesions; in 51/73 (69.9%) patients, all the lesions could also be characterized with CEUS. In the remaining cases, at least one lesion required additional imaging to determine whether it was malignant (14/73, 19.2%) or to establish its identity (22/73, 30.1%). In 4/73 (5.5%) patients, CEUS revealed additional lesions not detected on B-mode US.

CONCLUSIONS

CEUS alone was sufficient to classify 89.0% of the FLLs as benign or malignant, and in 80.8% it was also regarded as sufficient to identify the lesion. It served as a one-stop diagnostic test for 80.8% of the patients, reducing the need for CT-MR scans and providing savings in terms of radiation exposure, time, and money.

Transdermal estradiol improves bone density when used as single agent therapy for prostate cancer

PURPOSE

Current androgen deprivation therapies for men with prostate cancer cause accelerated osteoporosis and a significant risk of osteoporotic fracture. We have recently shown that transdermal estradiol is an effective alternative for such patients. Here we report the impact of transdermal estradiol therapy on the bone mineral density of men with prostate cancer.

MATERIALS AND METHODS

A total of 20 patients with newly diagnosed locally advanced or metastatic prostate cancer were treated with transdermal estradiol patches. Bone mineral density of the lumbar spine and the proximal femur was measured with dual-energy x-ray absorptiometry, and correlated with computerized tomography and isotope bone scan findings at 6-month intervals.

RESULTS

In all measured regions bone mineral density increased with time. By 1 year mean bone mineral density +/- SEM had increased by 3.60% +/- 1.6% in the lumbar spine (p = 0.055), 2.19% +/- 1.03% in the femoral neck (p = 0.055), 3.76% +/- 1.35% in the Ward's region (p = 0.008) and 1.90% +/- 0.85% in the total hip (p = 0.031), respectively. Of 12 osteoporotic sites 4 had improvement based on World Health Organization grading. All other sites improved toward a better classification.

CONCLUSIONS

Transdermal estradiol protects against bone loss in men with prostate cancer and may improve bone density in those at risk for osteoporotic fracture.

Developments in ultrasound contrast media

Ultrasound microbubble contrast agents are effective and safe echo enhancers. An ingenious array of methods are employed to achieve stability and provide a clinically useful enhancement period. Microbubbles enhance ultrasound signals by up to 25 dB (greater than 300-fold increase) due to resonant behaviour. This is used to rescue failed Doppler studies and may be extended to image the microcirculation of tumours and the myocardium using non-linear modes. Functional studies open up a whole range of applications by using a variety of active and passive quantitation techniques to derive indices from the transit of contrast through a tissue of interest. This has been especially successful in the detection of liver metastases and cirrhosis and shows great promise as a clinical tool. It also has great potential in measuring microcirculatory flow velocity. The demonstration that some microbubbles are not just pure blood pool agents but have a hepatosplenic specific phase has extended the versatility of ultrasound. Imaging of this stationary phase with non-linear modes such as phase inversion and stimulated acoustic emission, has improved the sensitivity and specificity of ultrasound in the detection and characterisation of focal liver lesions to rival that of CT and MR.

Does the presence of distant and local malignancy alter parenchymal perfusion in apparently disease-free areas of the liver?

Our objective was to investigate if hepatic arterial (HAP) and portal venous perfusion (PVP) in apparently normal areas of liver, as measured by functional CT, are affected by the presence of extra- and intrahepatic malignancy Three patient groups were compared: A, controls with no malignancy (N = 10); B, extrahepatic malignancy without liver involvement (N = 12); and C, subjects with metastases elsewhere in the liver (N = 13). HAP, PVP, and a CT hepatic perfusion index (CT-HPI) calculated as HAP/(HAP + PVP) were calculated on a section free of metastatic disease, using a previously published method. Figures for PVP were (median and interquartile range) in group A were 1.06 (0.9-1.30), in B 1.03 (0.81-1.09), and in C 0.75 (0.54-1.02) ml/min/ml; for HAP group A values were 0.07 (0.052-0.078), in B 0.07 (0.053-0.147), and in C 0.12 (0.091-0.146) ml/min/ml and for CT-HPI Group A values were 4.9% (4.8-6.6%), in B 5.6% (3.8-13.6%), and in C 14.3% (10.4-15.4%). Significant differences in all indices were seen between groups A and C. A significant difference (P = 0.017) was seen between groups B and C in the CT-HPI values. In conclusion, patients with liver metastases show abnormal blood flow in apparently normal liver compared to controls. This difference was not seen in subjects with malignancy without liver metastases. Possible explanations would be either the unmasking of occult metastatic disease or vasoactive or mechanical effects due to liver malignancy.

Do different types of liver lesions differ in their uptake of the microbubble contrast agent SH U 508A in the late liver phase? Early experience

PURPOSE

To compare the uptake of SH U 508A in different types of liver lesions by using stimulated acoustic emission.

MATERIALS AND METHODS

Thirty-seven patients with characterized lesions (metastasis, n = 17; hepatocellular carcinoma, n = 4; hemangioma, n = 9; focal nodular hyperplasia, n = 7) received 2.5 g SH U 508A. After 5 minutes, stimulated acoustic emission was elicited by using a previously described method. Liver and/or lesional differences were assessed with videodensitometry (objective conspicuity score), and two observers assessed each lesion by using a six-point scale (subjective conspicuity score).

RESULTS

Metastases and hepatocellular carcinoma had low stimulated acoustic emission; median objective conspicuity scores were 70% and 68% (all scores were > or =43%), respectively, and subjective conspicuity scores were 2 or higher for both observers. Hemangiomas had reduced stimulated acoustic emission, with more variability; the median objective conspicuity score was 41% (range, 9%-72%), and the median subjective conspicuity scores were 2 (range, 1-4) and 3.5 (range, 1-5) for observers 1 and 2, respectively. Focal nodular hyperplasia had stimulated acoustic emission comparable to that of the liver in all cases; the median objective conspicuity score was -4.7% (all scores were <6%), and the subjective conspicuity score was 1 or lower for both observers. This finding completely separated focal nodular hyperplasia and malignancies. Significant differences were seen between focal nodular hyperplasia and all other lesion types (P < .05).

CONCLUSION

Strong late-phase lesional uptake of SH U 508A is characteristic of focal nodular hyperplasia, is seen in some hemangiomas, and was not observed in malignancies.

Determination of glomerular filtration rate per unit renal volume using computerized tomography: correlation with conventional measures of total and divided renal function

PURPOSE

Previous studies suggest that functional computerized tomography (CT) can measure glomerular filtration rate (GFR) per unit renal volume. We compared this index with conventionally determined GFR measurements.

MATERIALS AND METHODS

A total of 16 men and 8 women 63.3 +/- 14.9 years old (range 31 to 88) were studied using with contrast enhanced CT. A single slice of kidney was scanned sequentially after bolus injection (0.5 to 1.0 ml. per second(-1)) of 20 ml. iopamidol (300 mg. iodine per ml.(-1)). GFR per volume of kidney was calculated using a Patlak graphical analysis, and this index was multiplied by renal volume on CT to yield global GFR (ml. per minute(-1)). Divided function was also calculated. GFR and divided renal function were calculated in all cases from radioisotope renography with 99m diethylenetetraminepentaacetic acid. In 12 subjects in whom 24-hour urine collection was possible GFR was also calculated from creatinine clearance.

RESULTS

A strong correlation was observed between divided renal function, expressed with respect to the right kidney calculated from CT (52.7 +/- 14.8%, range 19.9% to 97.4%) and by radioisotope renography (51.7 +/- 14.6%, range 18.9% to 92.6%, r = 0.97, p <0.0001). A strong correlation (r = 0.92, p <0.0001) was also seen between global GFR determined by CT (80.1 +/- 43.9 ml. per minute(-1), range 38.2 to 197.9) and creatinine clearance (72.4 +/- 47.5, range 14.6 to 168.5), and was stronger than the correlation between the radioisotope and creatinine clearance method (r = 0.67, p = 0.02) in the same patients.

CONCLUSION

Functional CT using nonionic contrast material can measure GFR normalized to renal volume and is an accurate alternative to conventional methods of renal function evaluation.

Functional CT imaging of the acute hyperemic response to radiation therapy of the prostate gland: early experience

PURPOSE

Functional CT can measure perfusion and permeability. We hypothesized that acute changes could be measured in these indexes following radiation therapy (RT) to the prostate gland.

METHOD

Twenty-two patients with prostatic cancer were studied before and 1-2 and 6-12 weeks after RT. A single section through the prostate was repeatedly scanned after contrast medium bolus injection. Contrast agent clearance per unit volume (alpha/V) and fractional vascular volume (fvv) were calculated using Patlak graphical analysis. Perfusion was calculated as the ratio between maximal rate of tissue enhancement and peak arterial enhancement.

RESULTS

Significant increases in all indexes occurred after RT. Mean perfusion rose from 0.122 to 0.263 ml/min/ml at 1-2 weeks, mean alpha/V increased from 0.0012 to 0.0016 ml/min/ml at 1-2 weeks, and mean fvv increased from 13.7 to 21% at 1-2 weeks. All three indexes remained elevated at 6-12 weeks after the start of RT.

CONCLUSION

Functional CT demonstrated an acute hyperemic response following RT to the prostate gland.

Hepatic malignancies: improved detection with pulse-inversion US in late phase of enhancement with SH U 508A-early experience

Twenty consecutive patients with known liver malignancies underwent ultrasonography (US) in conventional B mode and in pulse-inversion mode in the late hepatic-specific parenchymal phase after intravenous administration of SH U 508A, a microbubble US contrast agent. Two experienced readers assessed subjective and objective conspicuity, number of lesions, and smallest lesion diameter in each mode. Subjective and objective conspicuity were improved with pulse-inversion mode, and smaller lesions were depicted with pulse-inversion mode than with conventional B mode, improving the detection of metastases less than 1 cm in size.

Liver lesions: intermittent second-harmonic gray-scale US can increase conspicuity with microbubble contrast material-early experience

The authors investigated the effect of intermittent second-harmonic gray-scale (ISHGS) ultrasonography (US) with SH U 508A microbubbles on the conspicuity of focal liver lesions. Twenty-three patients were included in the study. Images were analyzed subjectively and quantitatively. Objective lesion conspicuity was increased. In 12 of the 15 patients with liver malignancy, gray-scale defects were seen in previously unsuspected areas. ISHGS US may improve the sensitivity of US for liver lesions.

Pulse-inversion mode imaging of liver specific microbubbles: improved detection of subcentimetre metastases

Pulse-inversion mode (a new ultrasound mode) can be used to image the late liver-specific parenchymal phase of the microbubble contrast-agent Levovist. Scanning in pulse-inversion mode after Levovist improves the detection of liver metastases and reveals more lesions of smaller size than conventional ultrasonography and computed tomography.

Twin fetuses: intravascular microbubble US contrast agent administration--early experience

PURPOSE

To explore the feasibility of administering SH U 508A by using a single-needle procedure at ultrasonography (US) in twin pregnancies to confirm interfetal transfusion in monochorionic twins and delineate placental angioarchitecture in pregnancies with twin-twin transfusion syndrome.

MATERIALS AND METHODS

Fourteen twin pregnancies were studied over 12 months: seven with monochorionic twins, including six with twin-twin transfusion syndrome; two of unknown chorionicity; and five with known dichorionic twins discordant for fetal karyotype or anomaly and undergoing selective feticide in the third trimester. Bolus injection of 100 microL/kg of estimated fetoplacental weight of 400 mg/mL of SH U 508A was performed in the intrahepatic vein of one twin, and evidence of interfetal transfusion was sought by means of digital analysis of power Doppler signals in the contralateral twin.

RESULTS

Contralateral twin echo enhancement was seen in four of the nine ultimately histopathologically proved monochorionic twins. As expected, no evidence of echo enhancement in the contralateral twin was seen in any of the five dichorionic twin pregnancies. There was no evidence of fetal compromise associated with the procedure.

CONCLUSION

These pilot results suggest that microbubbles can be used to demonstrate interfetal transfusion but not to delineate placental vascular anatomy.

[Stimulated acoustic emissions with the ultrasound contrast medium levovist: a clinically useful contrast effect with liver-specific properties]

PURPOSE

The purpose of this study was systematically to investigate stimulated acoustic emission (SAE) with the microbubble contrast agent Levovist (Schering AG, Berlin) in vivo with regards to reproducibility, distribution in various organs over time, dependence on technical factors, and influence on the delineation of focal liver lesions.

PATIENTS AND METHODS

2 intravenous injections of 1 g of Levovist were given to 2 dogs and 1-6 injections of 2.5 g Levovist to 5 healthy volunteers and 37 patients. The liver, spleen, large abdominal vessels, and kidney were intermittently scanned for up to 30 min. Studies were evaluated for the presence of SAE signals by 2 observers. In 20 patients with focal liver lesions (15 with metastases, 4 haemangiomata, 1 hepatocellular carcinoma, and 1 cyst) the influence on lesion visualization was also assessed.

RESULTS

SAE effects, lasting up to 30 minutes, were seen in all subjects in the liver and spleen. Vascular and renal SAE signals were noted shortly after injection, lasting up to 6 minutes. SAE was absent or markedly reduced in focal liver lesions, which were seen as colour voids. This increased the conspicuity of focal lesions, and in 5 patients additional metastases were detected that could not be delineated on B-mode alone.

CONCLUSION

A liver- and spleen-specific late phase of Levovist can be consistently demonstrated using SAE and the effect increases the conspicuity of focal liver lesions.

Stimulated acoustic emission to image a late liver and spleen-specific phase of Levovist in normal volunteers and patients with and without liver disease

Quantitative studies were performed to investigate liver- specific uptake of the microbubble Levovist, using stimulated acoustic emission (SAE), which can detect microbubbles even when stationary or slow-moving. These comprised studies of biodistribution comparing the liver and kidney in five normal volunteers, reproducibility in 34 patients, comparison between cirrhotics and controls (n = 9 each) and maximal depth of effect at different frequencies (180 measurements in 31 patients). Stimulated acoustic emission lasted beyond 30 min, with strongly liver-specific properties in each volunteer and was highly reproducible. No difference in the amount of SAE in the superficial liver was seen between cirrhotic and normal livers, but attenuation was higher in cirrhotics. This demonstrates a frequency-dependent effect on liver SAE penetration. We conclude that the liver uptake of Levovist lasts over 30 min, is reproducible, occurs even where diffuse liver disease is present and can be used to assess tissue attenuation in a novel fashion.

Functional renal perfusion imaging with colour mapping: is it a useful adjunct to spiral CT of in the assessment of abdominal aortic aneurysm (AAA)?

AIM

To ensure optimal timing with pre-operative spiral CT for abdominal aortic aneurysms (AAA), an initial 'timing' single level CT is commonly performed with a small bolus of contrast. This can be exploited to obtain adjunct functional information on renal perfusion. We have investigated the potential of this to measure renal perfusion, to produce colour renal perfusion maps and to predict surgical outcome in infrarenal aortic aneurysm assessment.

METHODS

We studied 21 patients being assessed for repair of infrarenal AAA. Prior to the spiral CT, a single level through the renal hili and aorta was scanned after the intravenous injection of 25 ml of contrast given at 10 ml/s. Ten 1 s duration scans were performed from 8 to 30 s after injection. Optimal timing for CT angiography can then be determined. Time-density curves were then drawn for both kidneys and aorta using regions of interest (ROIs) or pixel-by-pixel analysis. Renal cortical perfusion was measured using both ROI analysis and pseudocolour perfusion images. Following previous work, perfusion was calculated as the peak upslope of the tissue time density curve divided by peak aortic enhancement.

RESULTS

Cortical mean perfusion averaged 2.48 ml/min per ml (range 0.8-3.7 ml/min per ml n = 34) and the values obtained agreed with literature expectations. Follow up in the 10 patients proceeding to AAA repair suggest low mean perfusion values and predict a raised postoperative creatinine (P < 0.05)

CONCLUSIONS

Additional functional data and imaging can be obtained from the initial timing scan of a CT study, without requiring a dedicated study.

Non-invasive diagnosis of hepatic cirrhosis by transit-time analysis of an ultrasound contrast agent

BACKGROUND

Hepatic cirrhosis is accompanied by several haemodynamic changes including arterialisation of the liver, intrahepatic shunts, pulmonary arteriovenous shunts, and a hyperdynamic circulatory state. We postulated that the hepatic first pass of a bolus of an ultrasound contrast agent injected into a peripheral vein is accelerated in patients with cirrhosis. We investigated this first pass in patients with diffuse liver disease and in normal controls to assess whether it provides useful differential diagnostic information.

METHODS

We enrolled 15 patients with biopsy-proven cirrhosis, 12 patients with biopsy-proven non-cirrhotic diffuse liver disease, and 11 normal controls. We carried out continuous spectral doppler ultrasonography of a hepatic vein from 20 s before to 3 min after a peripheral intravenous bolus injection of 2.5 g Levovist. The intensity of the doppler signal was measured and used to plot time-intensity curves.

FINDINGS

Patients with cirrhosis showed a much earlier onset of enhancement (arrival time; mean 18.3 s) and peak enhancement (mean 55.5 s) than controls (49.8 s and 97.5 s) or patients with non-cirrhotic diffuse liver disease (35.8 s and 79.7 s). All patients with cirrhosis had an arrival time of the bolus of less than 24 s, whereas the arrival time was 24 s or more in 22 of the 23 other participants. Peak enhancement was higher in patients with cirrhosis (mean 48.7 units) than in the other two groups (12.5 and 12.3 units, respectively). We found highly significant differences between the patients with cirrhosis and each of the other two groups for all variables (p<0.005), whereas we found no significant differences between non-cirrhotic patients and controls.

INTERPRETATION

Our preliminary study suggests that analysis of liver transit time of a bolus of ultrasound contrast agent provides useful information about haemodynamic changes in patients with cirrhosis. Measurement of the arrival time of the bolus allows discrimination of patients with cirrhosis from controls and from patients with non-cirrhotic diffuse liver disease, and has potential as a non-invasive test for cirrhosis.

Use of contrast-enhanced computed tomography to measure clearance per unit renal volume: a novel measurement of renal function and fractional vascular volume

The iodinated contrast agents used for computed tomography (CT) have pharmacokinetics similar to inulin and can measure physiological indices, such as clearance per unit renal volume (alpha/V) and fractional vascular volume (fvv). Clinical experience with these techniques is, however, scanty, and the present study explored their potential in subjects with and without renal dysfunction. In a series of subjects, a single slice of kidney was scanned sequentially after the bolus injection of contrast material. Time-attenuation curves were constructed, and alpha/V and fvv were calculated using a Patlak graphic analysis. In the first part of the study, 50 normal kidneys in 35 subjects (aged 21 to 75 years) were studied. In the second stage, alpha/V was compared with glomerular filtration rate (GFR) measurements in 24 patients with diabetes (aged 28 to 84 years) with or without renal dysfunction. In normal kidneys, alpha/V averaged 0.49 +/- 0.11 mL/min/mL and fvv averaged 35% +/- 12%. These values agree with literature data obtained using other techniques. A negative correlation was seen between age and alpha/V (r = 0.66; P < 0.0001), but not fvv. In patients with diabetes, a strong correlation was observed between renal clearance values, calculated from CT and corrected for renal volume, and GFR (r = 0.87; P < 0.0001). Dynamic CT can provide quantitative renal physiological information on a regional basis noninvasively.

Improved imaging of liver metastases with stimulated acoustic emission in the late phase of enhancement with the US contrast agent SH U 508A: early experience

PURPOSE

To see whether stimulated acoustic emission (SAE) in the liver parenchyma in the late phase of enhancement with SH U 508A increases the conspicuity of occult metastases at ultrasonography (US).

MATERIALS AND METHODS

Eighteen patients with known hypo- or hypervascular hepatic metastases underwent US after SH U 508A administration, after a delay of at least 5 minutes, to ensure decay of blood pool enhancement. In 16 patients with visible metastases, conspicuity was compared on registered SAE and gray-scale scans by two blinded readers and by using computerized analysis of relative gray-scale and color Doppler conspicuity scores inside and outside the lesion. In nine patients, areas suspected of being involved but without definite gray-scale masses were imaged in the same way. Paired sections were analyzed by two blinded readers looking for parenchymal color defects without corresponding gray-scale masses; nine control images from three healthy volunteers were also included.

RESULTS

Intense, transient parenchymal SAE was seen in all subjects. All metastases appeared as areas of reduced or absent signal. The conspicuity score was 80% for SAE versus 9% for gray-scale US (P < .001, Wilcoxon signed rank test). SAE-specific defects were seen in all patients but in none of the volunteers. Metastases seen on SAE but undetectable on gray-scale images were proved in three patients.

CONCLUSION

SAE with SH U 508A improves the conspicuity of metastases. SAE-specific defects may reveal isoechoic or subtle metastases.

Liver vascular transit time analyzed with dynamic hepatic venography with bolus injections of an US contrast agent: early experience in seven patients with metastases

Spectral Doppler intensitometry to study transit of a bolus of an ultrasonographic (US) contrast agent in the hepatic veins was performed in seven patients suspected of having liver metastases and seven control subjects. All control subjects had a late response (rise time, > 25 seconds; time to peak intensity, > 45 seconds), whereas six of seven patients had an early response (rise time, < 25 seconds; time to peak intensity, < 45 seconds) (P < .01).

Prolongation and optimization of Doppler enhancement with a microbubble US contrast agent by using continuous infusion: preliminary experience

PURPOSE

To investigate whether continuous infusion of an echo-enhancing contrast agent for up to 15 minutes can provide uniform and prolonged enhancement.

MATERIALS AND METHODS

Six volunteers each received one bolus and three infusions of a microbubble contrast agent over 6-15 minutes at (a) a standard rate (mean, 2.08 mL/min), (b) a fast rate at twice the standard rate, and (c) a slow rate at half the standard rate. Spectral Doppler intensitometry of the femoral artery was performed for all infusions. Spectral Doppler ultrasound (US) scans of the femoral artery and color Doppler US scans of the carotid artery were subjectively assessed.

RESULTS

All infusions provided an equilibrium plateau of constant prolonged enhancement starting after 1-2 minutes and lasting until the end of the infusion. Enhancement at the plateau was +13 dB (slow rate), +17.1 dB (standard rate), and +18.3 dB (fast rate) compared with baseline. Saturation artifacts with infusions were markedly fewer than those with bolus injections. Dose effectiveness (duration of enhancement that measured at least 7.5 dB per gram of contrast agent) was markedly improved with the infusions, from 0.8 min/g for the bolus to 2.6 min/g for the slow infusion.

CONCLUSION

Continuous infusion of the microbubble contrast agent provided prolonged and uniform enhancement of Doppler signals and improved image quality by minimizing saturation artifacts.

Three-dimensional spiral CT angiography in pancreatic surgical planning using non-tailored protocols: comparison with conventional angiography

The aim of this study was to investigate three-dimensional spiral computed tomography (3DCT) as an adjunct to routine pancreatic CT scanning, with particular regard to the identification of surgically important hepatic arterial anomalies, correlated with conventional visceral angiography. 32 patients underwent spiral CT scans prior to pancreatic surgery using established protocols. Oral contrast medium was used throughout. 150 ml of intravenous contrast medium was given at 3 ml s-1 with a 24 s spiral CT sequence starting 35 s after the start of infusion. Two protocols were employed, both with a pitch of 1:3 mm table feed/collimation (n = 17) and 5 mm table feed/collimation (n = 15). Overlapping (1 mm minimum) axial reformats were reconstructed. 3DCT shaded-surface displays of the visceral arteries were assessed for visceral arterial anomalies. Visceral angiography (n = 23) was independently correlated. Satisfactory 3D angiograms were performed in all but one patient, in whom the coeliac axis was missed. (i) 3 mm protocol: 3DCT (n = 17) showed three anomalous right hepatic arteries (ARHA), one trifurcation anomaly and one splenic artery with an aortic origin. Angiography (n = 11) confirmed these findings, although one patient with an ARHA did not have angiography. A left gastric arterial supply to the left liver was not detected. (ii) 5 mm protocol: 3DCT (n = 15) showed two cases of ARHA. While confirming these findings, angiography (n = 12) showed a third case of ARHA, in which the coeliac and superior mesenteric artery had very close origins. A left gastric supply to the left liver was also missed. It is concluded that satisfactory 3DCT is possible without changing existing scanning protocols, although narrow sections are required for the confident assessment of right hepatic arterial anomalies, and any left hepatic supply via the left gastric artery was poorly assessed in this series.

Spiral computed tomography: principles and clinical use

Spiral computed tomography (CT) has been the major advance in CT in the 1990s. Its high speed and the three-dimensional nature of the obtained data sets has considerably improved the clinical performance of CT in many areas. Furthermore it has led to new applications such as CT angiography and virtual endoscopy.

The ureteric jet index: a novel measure of divided renal function

The aim of this study was to evaluate an index of divided renal function based on the quantification of the ureteric jets seen on colour Doppler ultrasound of the bladder. Thirty-one patients attending for scintigraphic renography underwent colour Doppler ultrasound with video recording for 5 min. Divided renal function was calculated as the proportion of jets from the right-sided orifice ('jet index'). This was compared with the corresponding 'scintigraphic index' found using Patlak-Rutland graphical analysis. Absolute discrepancies were calculated. Twenty-eight of thirty-one (90%) of studies were diagnostic for the calculation of jet indices. The mean jet index was 52% (n=28, SEM=5.8%) compared to a mean scintigraphic index of 54% (n = 28, SEM = 4.0%). The two scores were correlated, with a correlation coefficient of 0.72 and the median absolute difference between the two scores was 7.7%. Forty-three per cent (12/28) of subjects had discrepancies in the two scores of 5% or less. The score differences, however, showed a highly skewed distribution with 32% (9/28) subjects showing discrepancies over 20%. This discordant group (> 20% difference) included three patients with functional pelviureteric obstruction, one with a pelvic mass and one with an underfilled bladder. Two patients with very poor quality jets had impaired renal function. In one case, the index improved after angioplasty for renal artery stenosis. This simple test is a useful adjunct to urinary tract ultrasound but should be interpreted alongside evidence of renal obstruction, and complements rather than replaces existing tests.

Pre-operative classification of abdominal aortic aneurysms with spiral CT: the axial source images revisited

OBJECTIVE

The differentiation of supra-, juxta- and high infrarenal abdominal aortic aneurysms (AAA), which is essential for good surgical management, remains problematic. This prospective study assessed the value of highly overlapping vs. contiguous axial spiral computed tomography (CT) reconstructions in the pre-operative assessment of AAA.

PATIENTS AND METHODS

Thirty-five patients with abdominal aortic aneurysms were studied with spiral CT (10 mm collimation, pitch 1). Axial reconstructions were performed at 2 and 10 mm increments and compared with surgical findings. Using each protocol, the aneurysms were classified as infra-, juxta- or suprarenal. Observers also assessed visualization of main and accessory renal artery origins and identification of other surgically relevant vascular anomalies.

RESULTS

The 2 mm protocol correctly identified 29/31 infrarenal, 3/3 juxtarenal and 1/1 suprarenal aneurysms; two infrarenal aneurysms were overestimated as suprarenal. The 10 mm protocol correctly classified 25/31 infrarenal, 3/3 juxtarenal and 1/1 suprarenal aneurysms; five infrarenal aneurysms were overestimated as juxtarenal (n = 3) or suprarenal (n = 2) and one case was equivocal. Correct classification was thus 94% using the 2 mm protocol and 83% with the 10 mm protocol (P = 0.063). All 70 main renal artery origins were visualized with the 2 mm protocol, while the 10 mm protocol missed six (P = 0.03) The 2 mm protocol identified 10 accessory renal arteries, four of which were missed by the 10 mm protocol. Both protocols demonstrated five surgically relevant venous anomalies.

CONCLUSION

Spiral CT with highly overlapping axial reconstructions correctly classified 94% of abdominal aortic aneurysms; overlapping reconstructions were particularly useful in differentiating high infrarenal from juxtarenal aneurysms.

Bolus dynamics: theoretical and experimental aspects

This paper analyses the arterial enhancement produced by short intravenous boluses of iodinated contrast medium, with particular attention to the differences between various types of contrast media. A theoretical discussion is presented, followed by a small experimental study. The characteristics of the arterial time-attenuation curve are a function of the rate of contrast medium transit to the extracellular fluid (ECF), osmolality driven transit of water from the ECF into the plasma, direct effects on the heart and pulmonary circulation, the distribution of transit times in the cardiopulmonary circulation and recirculation. Theory predicts that while differences in peak arterial attenuation/peak height (PH) will be small, alterations in the areas under the time-attenuation curve (AUC) will reflect early-phase rate constants in the absence of major inotropic effects. The AUC should be higher for non-ionic than ionic media reflecting these lower rate constants. An experimental study on three healthy dogs confirmed these theoretical observations, with a slightly higher PH (6.5% higher) using a non-ionic medium but a substantially higher AUC (22% higher). (Differences significant at the 5% level, two-tailed paired t-test.) Our theoretical predictions and experimental findings suggest non-ionic media produce superior vascular enhancement, particularly shortly after injection. Possible clinical implications, particularly in dynamic enhanced computed tomography, are discussed.

Contrast media as extracellular fluid space markers: adaptation of the central volume theorem

We present some theoretical observations on the pharmacokinetics of the conventional intravascular radiographic and gadolinium chelate MR contrast agents. These agents may be viewed from a physiological perspective as extracellular fluid (ECF) space markers. It can be shown that the passage of such agents through the body may be described by a variant of the "central volume theorem", if the central volume is taken to be that of the entire extracellular fluid. A consequence is that, in a manner akin to nuclear medicine techniques utilizing technetium-99m diethylene triamine pentacetic acid (DTPA), measures of glomerular filtration rate (GFR) related to total ECF volume rather than to the normal body surface area may be obtained from direct or indirect measurements of iodine or gadolinium plasma levels. Typical measurements are presented. A simple means is also described of generating curves of the fraction of contrast medium excreted from the body, applicable to both patients with normal and with abnormal renal function.

Spontaneous dissections of the internal carotid artery: appearances on colour Doppler ultrasound

Spontaneous dissection of the internal carotid artery (ICA) is an unusual finding. We present an analysis of five patients (aged 40-60 years) with ICA dissections, describing the various flow patterns detected on colour Doppler ultrasound. Particular attention was paid to the presence of a dual lumen, the direction of flow in the false lumen and the velocity/spectral broadening of the Doppler trace obtained from the true and false lumens. Four different patterns were observed. Narrowing of the true lumen by the false lumen thrombus was seen in two cases with a low velocity Doppler waveform; three cases had a patent false lumen ("double lumen" pattern); the direction of flow in the patent false lumen varied from being (i) forward, (ii) reversed and (iii) bidirectional. The flow dynamics in carotid dissections are complex and are primarily dependent upon the presence of thrombus within the false lumen, the entry and exit flaps if the false lumen is patent, the motion of the flap wall and the extent of the dissection. They illustrate the diverse nature of the disease and Doppler ultrasound plays an important role in the imaging of ICA dissections.

Splenic blood flow: evaluation with computed tomography

RATIONALE AND OBJECTIVES

To study splenic perfusion with use of computed tomography (CT).

METHODS

Twenty-six control patients without splenoportal disease, six with cirrhosis, and seven with other splenic disease were examined with electron-beam CT. Twenty-five milliliters of iohexol (300 mg of iodine per milliliter) was given intravenously at 10 mL/sec followed by a saline bolus. Multiple single-level axial sections were acquired 8-90 seconds after injection. Perfusion was calculated by dividing maximal splenic enhancement by the area under the circulation-corrected aortic time-enhancement curve. Subjective assessments of enhancement heterogeneity were made, and regional perfusion was calculated in 10 patients with heterogeneous enhancement. Total splenic volume and blood flow were computed in 21 patients.

RESULTS

Mean perfusion (controls: 1.29 mL/min/mL, miscellaneous group: 1.07 mL/min/mL) was close to predictions. There was a trend toward lower perfusion in cirrhotic patients (0.87 mL/min/mL), but the difference was not statistically significant. Total splenic blood was increased in patients with cirrhosis (P < .01). Marked perfusion heterogeneity was observed in 41% of spleens, but by 2 minutes splenic enhancement was uniform.

CONCLUSION

CT shows promise in the study of splenic blood flow.

Review article: the quantification of renal function with enhanced computed tomography

The changes with time in renal parenchymal and vascular attenuation following injection of an intravascular contrast medium can be exploited to study renal physiology in several ways. Shortly after injection, both contrast medium clearance and fractional vascular volume per unit volume of kidney can be measured on a regional basis by obtaining sequential CT data from one anatomical level and the application of a graphical analysis to the baseline subtracted CT numbers for tissue and vascular regions of interest: c(t) and b(t), respectively. By plotting the ratio c(t)/b(t) against integral of b(t)dt/b(t), both fractional vascular volume and contrast medium clearance can be estimated graphically. At later time points, a semilogarithmic plot against time of the declining attenuation of vascular or parenchymal regions of interest gives information about overall, as opposed to regional, renal function: the gradient estimates the glomerular filtration rate per unit volume of extracellular fluid. Absolute glomerular filtration rates can also be calculated with blood sampling. Although further experimental evaluation is needed, these techniques have a strong theoretical basis, and experimental work performed so far is encouraging. Possible applications of these techniques are discussed.

Differentiating between T1 and T2* changes caused by gadopentetate dimeglumine in the kidney by using a double-echo dynamic MR imaging sequence

Dynamic MR images of the passage of gadopentetate dimeglumine through the kidneys of normal rats are obtained using a dual gradient-echo sequence. The amplitudes of gradient echoes are defined by local T1 and T2* values in the tissue. The ratio of these amplitudes, primarily defined by local T2*, can be used to differentiate between T1 and T2* effects. This is particularly important with regard to renal studies because, due to a highly inhomogeneous distribution of gadopentetate dimeglumine in the kidney, T2* shortening can impede MR data analysis. To study changes in the observed signal caused by gadopentetate dimeglumine, curves of MR renal intensity versus time were obtained in the cortex and medulla after administration of the contrast agent. Using T2* compensation, distinct temporal peaks were observed in the cortex and outer medulla, indicating a high concentration of gadopentetate dimeglumine in the vascular phase. The authors conclude that this technique can be a useful tool for studying renal function noninvasively.

Contrast media as extracellular fluid space markers: adaptation of the central volume theorem

We present some theoretical observations on the pharmacokinetics of the conventional intravascular radiographic and gadolinium chelate MR contrast agents. These agents may be viewed from a physiological perspective as extracellular fluid (ECF) space markers. It can be shown that the passage of such agents through the body may be described by a variant of the "central volume theorem", if the central volume is taken to be that of the entire extracellular fluid. A consequence is that, in a manner akin to nuclear medicine techniques utilizing technetium-99m diethylene triamine pentacetic acid (DTPA), measures of glomerular filtration rate (GFR) related to total ECF volume rather than to the normal body surface area may be obtained from direct or indirect measurements of iodine or gadolinium plasma levels. Typical measurements are presented. A simple means is also described of generating curves of the fraction of contrast medium excreted from the body, applicable to both patients with normal and with abnormal renal function.

Penetration of the holmium:YAG laser through fluid

PURPOSE

The 2.1-microns pulsed holmium:yttrium-aluminum-garnet (Ho:YAG) laser combines the properties of transmissibility down a flexible silica fiber, enabling percutaneous or endoscopic use, with high water absorption, suggesting good safety characteristics. Laser attenuation in practice, however, is an extremely complex process. The authors studied its effective penetration through blood, bile, urine, saline, and contrast media.

MATERIALS AND METHODS

With use of a fiberoptically directed beam and a laser power meter, penetration was measured in vitro with the fiber tip separated from the medium by 5 cm (noncontact mode) and with the fiber tip immersed (contact mode). Logarithm of energy falloff was measured against fluid thickness. Attenuation coefficients (mu) and half value layer (HVL) distances (estimated thickness of fluid needed to have power) were measured.

RESULTS

In noncontact mode, power falloff was exponential. Non-sanguinous media had similar values for mu and HVL (mu = 2.24-2.70 mm-1 and HVL = 0.26-0.31 mm) close to theoretical predictions. Blood caused significantly (P < .05) more attenuation (mu = 5.15 mm-1, HVL = 0.13 mm). In contact mode, attenuation was much more complex with "plateau" distances of up to 1.2 mm, below which attenuation was negligible. The HVL distances ranged from 0.9 to 1.8 mm and were up to 14 times higher. The main reason is probably the formation of microcavities around the fiber tip.

CONCLUSION

The effective penetration of this laser when immersed may be several times that predicted, with important clinical implications.

Liver perfusion studied with ultrafast CT

OBJECTIVE

Our goal was to quantify absolute hepatic arterial and portal venous perfusion noninvasively in patients with and without liver disease using ultrafast CT.

MATERIALS AND METHODS

A single slice through the porta hepatis was repeatedly scanned after bolus injection of 25 ml of iohexol 300 mg I/ml, followed by a 25 ml saline "chaser" intravenously at 10 ml/s. Thirty-nine controls, 7 cirrhotic patients, and 5 patients with known metastases on the slice plane were studied; hepatic arterial perfusion was determined in 41 patients and portal venous perfusion in 24. Time-attenuation curves from regions of interest drawn over the liver, spleen, aorta, and portal vein were analysed. Hepatic arterial perfusion was calculated by dividing the peak gradient of the liver time-attenuation curve prior to the time of peak splenic attenuation by the peak aortic CT number increase. Splenic perfusion was calculated by dividing the peak gradient of the splenic time-attenuation curve by the peak aortic CT number increase. Portal perfusion was derived by scaling the splenic time-attenuation curve by the ratio of hepatic arterial/splenic perfusion. This scaled curve was subtracted from the liver time-attenuation curve to give a portal curve. The peak up-slope of this curve was divided by the peak rise in splenic or portal vein density.

RESULTS

Hepatic arterial perfusion averaged 0.19 ml/min/ml (n = 31) in controls and was raised in cirrhosis to 0.25 ml/min/ml (n = 6) and metastases 0.43 ml/min/ml (n = 4). Portal venous perfusion was 0.93 ml/min/ml (n = 19) in controls and 0.43 ml/min/ml (n = 4) in cirrhosis. Reproducibility has been confirmed.

CONCLUSION

Dynamic ultrafast CT shows potential in quantifying arterial and portal hepatic perfusion. The technique may be adaptable to dynamic bolus MRI.

Holmium-YAG laser for gall stone fragmentation: an endoscopic tool

A systematic review of the 2.1 mu holmium-YAG laser for gall stone lithotripsy was undertaken. This infrared laser, which can be used endoscopically and percutaneously, has safety advantages over other lasers and has potential as a general purpose vascular and surgical tool. Twenty nine gall stones (mean mass 1.3 g) were fragmented in vitro using pulse energies of 114 to 159 mJ/pulse at 5 Hz with a 0.6 mm fibre, while being held in an endoscopy basket. All stones were successfully fragmented, requiring an average of 566 pulses with a 5 Hz pulse repetition frequency. The number of pulses required increased with gall stone size and mass (p < 0.01), and decreased with both pulse energy (p < 0.01) and operator experience (p < 0.05). The biochemical content of the stone did not significantly affect the number of pulses needed. The potential hazard of the laser to the biliary endothelium was investigated. At the pulse energies used, five pulses at close contact penetrated into the serosa of fresh gall bladder wall. No damage was seen when two pulses were fired. This laser shows considerable promise in gall stone lithotripsy. Until further safety data are available, however, its use with endoscopic vision is advised.

Case report: a gastroduodenal artery pseudoaneurysm presenting with obstructive jaundice and treated by arterial embolization

A case of obstructive jaundice due to a pseudoaneurysm of the gastroduodenal artery is reported. This was successfully embolized, with relief of the jaundice. Relief of biliary obstruction by aneurysm embolization has not, to our knowledge, been previously described.

Contrast bolus dynamic computed tomography for the measurement of solid organ perfusion

RATIONALE AND OBJECTIVES

The authors have investigated the aortic responses to various intravenous bolus injections of nonionic and ionic contrast media and have presented data illustrating the potential of ultrafast computed tomography (CT) to quantify perfusion in the kidney, liver, and spleen.

METHODS

Bolus Dynamics Study: Performed in 3 healthy dogs (weight: 35 kg to 36 kg). In 2 dogs, 15 mL of the nonionic agent iohexol and the ionic agent sodium-meglumine diatrizoate were injected at 5, 10 and 20 mL/sec via a venous catheter placed in the superior vena cava; the order of injection was alternated between the 2 dogs. In the third dog, 25 mL of iohexol 300 mg I/mL was compared with diatrizoate 370 mg I/mL with injection rates of 10 and 20 mL/sec. Computed tomography scanning at the level of the midabdominal aorta was performed using an ultrafast CT scanner. Time-density curves were drawn for regions of interest over the aorta, and gamma-variate fits performed. Perfusion Studies: Dynamic perfusion scans of the upper abdomen were performed in more than 50 patients. A dose of 25 mL of iohexol 300 mg I/mL was injected at 10 mL/sec via an intravenous cannula in the antecubital fossa, followed immediately by 25 mL of saline, at the same rate. Scanning was performed at a single level using an ultrafast CT scanner. Regions of interest were drawn and gamma-variate fits were applied to the vascular time-density curves.

RESULTS

Bolus Dynamics: Excellent curve fits for aortic time-density curves were obtained. A 10-mL/sec versus a 5-mL/sec bolus produced an 8% higher peak density. Nonionic contrast increased the peak density by a mean of 6%, increased the area under the corrected time-density curve by a mean of 22%, and lengthened the increase time by a mean of 21%. Perfusion Studies: Values obtained were reproducible and correlated well with values predicted from inert gas washout techniques.

CONCLUSIONS

Changes in the CT number in a region after an intravenous injection of contrast medium may be used to calculate blood flow per unit volume of tissue. Ultrafast CT offers sufficient data points for accurate calculation. The quality of the aortic bolus is of great importance. Nonionic media offer several important advantages: hemodynamic perturbation is minimized, and they are better tolerated at the high injection rates needed. Low-osmolality nonionic agents produce "better" curves than conventional high-osmolality ionic agents, all other factors being equal. The resulting data are relevant to intravenous digital subtraction angiography and indirect portography as well as to perfusion measurement. The technique of quantitative dynamic CT is theoretically applicable to any cross-sectional modality, notably magnetic resonance.

Percutaneous renal biopsy in the district general hospital

This paper reports a retrospective study of the clinical value of percutaneous renal biopsy in secondary referral centres. Between 1984-90, 205 patients over the age of 16 had 218 biopsies at three district general hospitals. Adequate tissue was obtained in 194 patients (95%, 89% of the biopsies). Significant complications occurred in only four patients. In 170 patients (83%) the biopsy yielded information of diagnostic and prognostic value and influenced management. The main indications for biopsy were nephrotic syndrome, in 63 patients, and chronic renal failure, in 58 patients. The most frequent findings were minimal change disease, focal segmental glomerulosclerosis, IgA nephropathy, membranous glomerulonephritis and mesangiocapillary glomerulonephritis. The most obvious association between indication and histology was between haematuria and IgA nephropathy. Percutaneous renal biopsy in the district general hospital in patients selected by a nephrologist and performed by experienced or supervised operators is a safe procedure. There is a high yield of renal tissue which is of clinical value in patient care.