Quantification of hepatic and renal cortical echogenicity in clinically normal cats

Evaluation of renal cortical echogenicity in healthy cats using anisotropic backscatter artifacts and echogenicity differences among internal organs

BACKGROUND

Renal cortical anisotropic backscatter artifact (CABA) is a hyperechoic region of the renal poles where the insonation of sound beams is perpendicular to the renal tubules within the renal cortex.

AIMS

To determine whether renal CABA can be observed in healthy cats and to compare the echogenicity of renal CABA with that of the spleen and liver.

MATERIAL AND METHODS

Images of the spleen, liver, kidneys, and urinary bladder were acquired from 30 clinically healthy cats with renal CABA. Echogenicity differences among organs and echo scores within urine were recorded and analyzed. All ultrasound images were acquired using a 7.2-14-MHz linear transducer. Univariate logistic regression was used to assess the associations between the presence of renal CABA and various variables.

RESULTS

The prevalence of the renal CABA was 86.7% (26/30) and 93.3% (28/30) according to different observers. The reproducibility of renal CABA is substantial to excellent. The renal CABA echogenicity was greater or equal to the spleen and greater than the hepatic echogenicity in 90.0% of cats (27/30). For comparison with the spleen and liver, there were three and six combinations of echogenicity differences using the CABA and non-CABA regions, respectively. The renal cortical echogenicity in the CABA region was higher than the liver in all subjects. Renal CABA was not associated with age, body weight, gender, body condition score, or lipid droplets in the urinary bladder.

CONCLUSION

Renal CABA was present in most healthy cats and could be used for echogenicity comparisons with the liver and spleen.

Preliminary Evaluation of Cortical and Medullary Echogenicity in Normal Canine Fetal Kidneys during the Last 10 Days of Pregnancy

The objective of this study was to assess changes in the echogenicity of the cortex and medulla of canine fetal kidneys in relation to days before parturition (dbp), maternal size and litter size. Monitoring of 10 healthy pregnant bitches (2-8 years old, 8.8-40.3 kg bw) was conducted from -10 to 0 dbp using ultrasound. A single renal sonogram was obtained by scanning in a longitudinal section the three most caudal fetuses. The mean gray level (MGL) and SD of a manually drawn region of interest (ROI) in the renal cortex and medulla were measured using the Fiji Image J software (Image J 1.51h, Java 1.6 0_24 64 bit). A linear mixed model taking into account the maternal size as a fixed effect, dbp and litter size as covariates and the bitch as a random and repeated effect was used. The regression coefficients (b) were estimated. Cortical SD (C-SD) and cortico-medullary SD (C/M-SD) were influenced by dbp, with a significant decrease at the approaching day of parturition (b = 0.23 ± 0.06, p < 0.001 and b = 0.5 ± 0.02, p = 0.038, respectively). Maternal size had a significant impact on C/M-MGL with differences observed in large-sized (1.95 ± 0.13) compared to small- (1.41 ± 0.10, p = 0.027) and medium-sized bitches (1.51 ± 0.09, p = 0.016). The C/M-MGL was influenced by litter size, showing a decrease as the number of pups increased (b = -0.08 ± 0.03, p = 0.018). C-SD and C/M-SD were exclusively affected by dbp, and not by maternal and litter size. This suggests their potential as valuable parameters, warranting further investigations in future studies.

The ultrasonographic appearance of renal medullary striations and their association with renal disease and renal histopathology in domestic cats

Medullary striations (MS) have been anecdotally observed on ultrasound of feline kidneys; however, their significance is unknown. Aims of this retrospective, case control, pilot study were to describe the appearance, prevalence, and clinicopathological correlates of MS in a referral feline population. Still images from 1247 feline abdominal ultrasound studies performed between 2011 and 2021 were reviewed. Cats with MS were identified and compared with age-matched controls. Serum urea, creatinine, calcium, phosphate, and calcium-phosphate-product, plus urine specific gravity, urine protein: creatinine ratio (UPC), prevalence of active sediment (defined as > 5 red (RBC) or white blood cells (WBC) per high-power field) and prevalence of positive urine culture were compared between MS and control groups using the Mann-Whitney U test or Fisher's Exact test. Data are presented as median [range]. 27 cats were identified as having MS, giving a prevalence of 2.2% with a significantly higher proportion being seen in males (P = 0.018). Medullary striation cats had significantly higher UPC values than controls (0.46 [0.16-7.57] vs. 0.16 [0.07-2.27]; P = 0.006). Cats with MS were more likely to have active urinary sediments (39% vs 8%, P = 0.023), but no difference in prevalence of positive urinary cultures was observed between groups. There was no significant difference in other parameters between MS and control cats. Renal histopathology performed in three MS cats revealed focal regions of linear medullary fibrosis. Medullary striations are associated with proteinuria and urinary tract inflammation in cats, which may reflect renal tubular dysfunction and/or inflammation. Hence identification might allow for earlier detection of renal pathology.

Artificial intelligence in veterinary diagnostic imaging: A literature review

Artificial intelligence in veterinary medicine is an emerging field. Machine learning, a subfield of artificial intelligence, allows computer programs to analyze large imaging datasets and learn to perform tasks relevant to veterinary diagnostic imaging. This review summarizes the small, yet growing body of artificial intelligence literature in veterinary imaging, provides necessary background to understand these papers, and provides author commentary on the state of the field. To date, less than 40 peer-reviewed publications have utilized machine learning to perform imaging-associated tasks across multiple anatomic regions in veterinary clinical and biomedical research. Major challenges in this field include collection and cleaning of sufficient image data, selection of high-quality ground truth labels, formation of relationships between veterinary and machine learning professionals, and closure of the gap between academic uses of artificial intelligence and currently available commercial products. Further development of artificial intelligence has the potential to help meet the growing need for radiological services through applications in workflow, quality control, and image interpretation for both general practitioners and radiologists.

ACVR and ECVDI Consensus Statement for the Standardization of the Abdominal Ultrasound Examination

This consensus statement is designed to provide a standard of care document and describes the ACVR and ECVDI definition for performing a standard abdominal ultrasound examination in dogs and cats. The ACVR and ECVDI define a standard abdominal ultrasonographic examination as a complete exam of the abdominal organs which is appropriately documented. The consensus statement intends to provide guidance to veterinary sonographers and veterinarians for the performance and documentation of high-quality diagnostic ultrasound examination. The document may also serve as a teaching aid for veterinary students, veterinarians, and residents in diagnostic imaging who seek proficiency in diagnostic ultrasound. Finally, it may serve an additional role in educating the public as to what a high-quality abdominal ultrasound examination should entail.

Absence of renal cortical anisotropic backscattering artifact in feline chronic kidney disease

Renal cortical anisotropy backscattering artifact (CABA) is a focal hyperechoic region where the tubules are parallel to the incident ultrasound beam, reflecting most of the beams to the transducer. To investigate the association between chronic kidney disease (CKD) and the absence of renal CABA in cats. Ultrasonographic renal images of 40 cats with CKD (stage II-IV) and 36 clinically healthy cats were blindly evaluated by two observers to determine the visibility of renal CABA. Inter- and intraobserver agreements were evaluated using McNemar's test. The association between the absence of renal CABA and CKD was assessed using Fisher's exact test. Excellent intraobserver and substantial interobserver agreements were demonstrated. A significant association (P < .0001) between absent renal CABA and CKD stage was revealed in all cats. Cats with CKD had an increased risk of the absence of renal CABA (Odds ratio, 56.0; 95% CI, 13.8-227.0) compared with the clinically healthy cats. The absence of renal CABA revealed 87.5% sensitivity and 88.9% specificity to detect CKD in all cats, and 91.7% sensitivity and 83.3% specificity in aged cats. Our study demonstrated a correlation between feline CKD and the absence of renal CABA, providing a feasible and alternative method for feline CKD evaluation.

Feline abdominal ultrasonography: what's normal? what's abnormal? The kidneys and perinephric space

PRACTICAL RELEVANCE

Abdominal ultrasound plays a vital role in the diagnostic work-up of many cats presenting to general and specialist practitioners. Ultrasound examination of the kidneys and perinephric space can provide important information on several conditions including chronic renal disease, hydronephrosis and perinephric pseudocyst formation.

CLINICAL CHALLENGES

Despite ultrasonography being a commonly used modality, many practitioners are not comfortable performing an ultrasound examination or interpreting the resulting images. Even for the experienced ultrasonographer, differentiating between incidental findings, such as a medullary rim sign, and pathological changes can be challenging.

AIM

This review, part of an occasional series on feline abdominal ultrasonography, discusses ultrasonographic examination of the normal and diseased kidney and perinephric space. Aimed at general practitioners who wish to improve their knowledge of and confidence in feline abdominal ultrasound, this review is accompanied by high-resolution images and videos available online as supplementary material. A subsequent article will address ultrasonography of the collecting system including the renal pelvis and urinary bladder.

EQUIPMENT

Ultrasound facilities are readily available to most practitioners, although use of ultrasonography as a diagnostic tool is highly dependent on operator experience.

EVIDENCE BASE

Information provided in this article is drawn from the published literature and the author's own clinical experience.

The ultrasonographic medullary "rim sign" versus medullary "band sign" in cats and their association with renal disease

BACKGROUND

Medullary rim sign (MRS) refers to a hyperechoic line in the renal medulla, reported on ultrasound examination (US) in both dogs and cats with and without kidney disease (KD).

OBJECTIVE

To describe the different aspects of MRS in cats and to assess its association with KD.

ANIMALS

Cats that underwent US examination, with MRS (study group) with and without KD and without MRS with and without KD (control groups).

METHODS

Retrospective case-control study: cats with MRS, with or without KD (rim sign groups) and cats without MRS, with or without KD (control groups). Ultrasonographic images were blindly reviewed with attention given to the thickness and margins of the MRS recorded.

RESULTS

Eighty-four cats with MRS were included and 60 cats recruited for each control group. The MRS had 2 distinct aspects: a thin hyperechoic line with well-defined margins (MRS-line) in 50/84 cats (59%) and a thick hyperechoic band with ill-defined margins (MRS-band) in 34/84 cats (41%). Twenty of 50 (40%) cats with MRS-line and 25/34 (74%) of cats with MRS-band had KD. The frequency of MRS-line was higher in cats without KD, whereas the presence of MRS-band was more frequent in cats with KD (P = .003).

CONCLUSIONS AND CLINICAL IMPORTANCE

A thick hyperechoic ill-defined band (for which the term medullary band sign is proposed) was more frequently associated with KD, whereas a thin hyperechoic well-defined line (true MRS) may be seen in cats with or without KD.

Use of deep learning to detect cardiomegaly on thoracic radiographs in dogs

The purpose of this study was to develop a computer-aided detection (CAD) device based on convolutional neural networks (CNNs) to detect cardiomegaly from plain radiographs in dogs. Right lateral chest radiographs (n = 1465) were retrospectively selected from archives. The radiographs were classified as having a normal cardiac silhouette (No-vertebral heart scale [VHS]-Cardiomegaly) or an enlarged cardiac silhouette (VHS-Cardiomegaly) based on the breed-specific VHS. The database was divided into a training set (1153 images) and a test set (315 images). The diagnostic accuracy of four different CNN models in the detection of cardiomegaly was calculated using the test set. All tested models had an area under the curve >0.9, demonstrating high diagnostic accuracy. There was a statistically significant difference between Model C and the remainder models (Model A vs. Model C, P = 0.0298; Model B vs. Model C, P = 0.003; Model C vs. Model D, P = 0.0018), but there were no significant differences between other combinations of models (Model A vs. Model B, P = 0.395; Model A vs. Model D, P = 0.128; Model B vs. Model D, P = 0.373). Convolutional neural networks could therefore assist veterinarians in detecting cardiomegaly in dogs from plain radiographs.

Feline abdominal ultrasonography: what's normal? what's abnormal? The liver

PRACTICAL RELEVANCE

Abdominal ultrasound plays a vital role in the diagnostic work-up of many cats presenting to general and specialist practitioners. Ultrasound examination of the liver can be key in the diagnosis of diseases such as hepatic lipidosis and hepatic neoplasia.

CLINICAL CHALLENGES

Despite ultrasonography being a commonly used modality, many practitioners are not comfortable performing an ultrasound examination or interpreting the resulting images. Even differentiating between normal variation and pathological changes can be challenging for all but the most experienced. When assessing the liver via ultrasound, a diffuse alteration in liver echogenicity may be difficult to detect unless the change is marked and, although comparisons can be made with the spleen and kidneys, this relies on these organs being normal.

EQUIPMENT

Ultrasound facilities are readily available to most practitioners, although use of ultrasonography as a diagnostic tool is highly dependent on operator experience.

AIM

This review, the first in an occasional series on feline abdominal ultrasonography, discusses ultrasonographic examination of the normal and diseased liver, with focus on the liver parenchyma. It is aimed at general practitioners who wish to improve their knowledge of and confidence in feline abdominal ultrasound and is accompanied by high-resolution images. Ultrasound-guided sampling of the liver is also covered. Future articles will discuss the biliary tree and hepatic vascular anomalies.

EVIDENCE BASE

Information provided in this article is drawn from the published literature and the author's own clinical experience.

Non-invasive quantification of hepatic fat content in healthy dogs by using proton magnetic resonance spectroscopy and dual gradient echo magnetic resonance imaging

The objective of the present study was to describe two non-invasive methods for fat quantification in normal canine liver by using magnetic resonance imaging (MRI) and spectroscopy. Eleven adult beagle dogs were anesthetized and underwent magnetic resonance examination of the cranial abdomen by performing morphologic, modified Dixon (mDixon) dual gradient echo sequence, and proton magnetic resonance spectroscopy (¹H MRS) imaging. In addition, ultrasonographic liver examination was performed, fine-needle liver aspirates and liver biopsies were obtained, and hepatic triglyceride content was assayed. Ultrasonographic, cytologic, and histologic examination results were unremarkable in all cases. The median hepatic fat fraction calculated was 2.1% (range, 1.3%-5.5%) using mDixon, 0.3% (range, 0.1%-1.0%) using ¹H MRS, and 1.6% (range 1.0%-2.5%) based on triglyceride content. The hepatic fat fractions calculated using mDixon and ¹H MRS imaging were highly correlated to that based on triglyceride content. A weak correlation between mDixon and ¹H MRS imaging was detected. The results show that hepatic fat content can be estimated using non-invasive techniques (mDixon or ¹H MRS) in healthy dogs. Further studies are warranted to evaluate the use of these techniques in dogs with varying hepatic fat content and different hepatic disorders.

Qualitative and quantitative ultrasound attributes of maternal-foetal structures in pregnant ewes

The aim of this study was to examine foetal organs and placental tissue to establish a correlation between the changes in the composition of these structures associated with their maturation and the ultrasonographic characteristics of the images. Twenty-four pregnant ewes were included in the study. Ultrasonography assessments were performed in B-mode, from the ninth gestational week until parturition. The lungs, liver and kidneys of foetuses and placentomes were located in transverse and longitudinal sections to evaluate the echogenicity (hypoechoic, isoechoic, hyperechoic or mixed) and echotexture (homogeneous and heterogeneous) of the tissues of interest. For quantitative evaluation of the ultrasonographic characteristics, it was performed a computerized image analysis using a commercial software (Image ProPlus^® ). Mean numerical pixel values (NPVs), pixel heterogeneity (standard deviation of NPVs) and minimum and maximum pixel values were measured by selecting five circular regions of interest in each assessed tissue. All evaluated tissues presented significant variations in the NPVs, except for the liver. Pulmonary NPVmean, NPVmin and NPVmax decreased gradually through gestational weeks. The renal parameters gradually decreased with the advancement of the gestational weeks until the 17th week and later stabilized. The placentome NPVmean, NPVmin and NPVmax decreased gradually over the course of weeks. The hepatic tissue did not show echogenicity and echotexture variations and presented medium echogenicity and homogeneous echotexture throughout the experimental period. It was concluded that pixels numerical evaluation of maternal-foetal tissues was applicable and allowed the identification of quantitative ultrasonographic characteristics showing changes in echogenicity related to gestational age.

Comparison of ultrasonographic findings in cats with and without azotaemia

Objectives

The objective of this study was to identify the renal ultrasonographic (US) findings most strongly associated with azotaemia in cats.

Methods

US findings in 238 cats with (serum creatinine >180 μmol/l) and 270 cats without azotaemia were compared in a retrospective case-control study. Cats with pre-renal azotaemia or urethral obstruction were excluded. Data extracted from the medical records included age, body weight and body condition score (BCS). Quantitative and subjective US findings were extracted from archived ultrasound images and contemporaneous reports.

Results

In non-azotaemic cats, mean ± SD renal length was 40.1 ± 5.5 mm. Male cats had larger kidneys than female cats (mean difference 5.2 mm; P = 0.001) and, on average, the right kidney was slightly larger than the left (mean difference 1.6 mm; P = 0.01). Azotaemic cats had significantly lower mean body weight and BCS, and greater mean age and renal pelvic diameter. Renal pelvic diameter was negatively correlated with urine specific gravity (ρ –0.44, P <0.001). Compared with non-azotaemic cats, there was no difference in mean renal length of azotaemic cats because the numbers with enlarged kidneys and small kidneys were similar. Radiologists’ subjective assessments of renal size differed markedly between azotaemic and non-azotaemic cats, with azotaemic cats more likely to be recorded falsely as having abnormally small or enlarged kidneys. US findings significantly associated with azotaemia were perinephric fluid (odds ratio [OR] 26.4, 95% confidence interval [CI] 3.4–207.7), small kidneys (OR 8.4, 95% CI 4.0–17.4), hyperechoic renal cortex (OR 4.1, 95% CI 2.2–7.6), loss of corticomedullary differentiation (OR 4.1, 95% CI 1.8–9.6), renal calculi (OR 2.7, 95% CI 1.4–4.9), enlarged kidneys (OR 2.5, 95% CI 1.2–5.5) and dilated renal pelvis (OR 1.6, 95% CI 1.3–1.9).

Conclusions and relevance

Perinephric fluid was the US finding most strongly associated with azotaemia in this study and may merit more emphasis than it has received to date. Bias in radiologists’ subjective assessments of renal size suggests that other subjective findings will also be biased.

Diagnostic utility of renal fine-needle aspirate cytology and ultrasound in the cat

Objectives

The primary objective of this study was to retrospectively assess the diagnostic utility of feline renal fine-needle aspiration cytology by assessing diagnostic yield, cytologic characteristics and diagnostic accuracy. The secondary objective was to characterize ultrasonographic features of sampled kidneys to determine if they influenced diagnostic yield.

Methods

Slides, images and patient data were collected from the University of Minnesota Veterinary Medical Center database. Slides were designated as diagnostic or non-diagnostic. Non-diagnostic slides were used in calculating diagnostic yield and excluded from other analysis. Slides were evaluated for cytologic characteristics and assigned a single primary diagnosis. Ultrasound still images were evaluated for descriptive characteristics and characteristics of specific lesions were described. Cases with confirmatory testing were used to determine diagnostic sensitivity, specificity and positive and negative predictive values for detecting neoplasia.

Results

Of 96 cytologic submissions available for review, diagnostic yield was 68%; 48% of samples were at least moderately cellular. Of 87 cases with ultrasound data, kidneys showing subcapsular renal infiltrate, diffuse renal enlargement without pelvic dilation and infiltrative/nodular change were more likely to yield diagnostic samples. Of 12 confirmed cases, cytology was 100% sensitive and specific for the detection of neoplasia (four round-cell tumors and two carcinomas). Three cases with non-neoplastic histologic diagnoses were considered cytologically normal, two incorrectly diagnosed the pathology present, and one correctly diagnosed the pathology. While some imaging characteristics were more commonly seen in neoplastic vs non-neoplastic lesions, the sample size was insufficient for definitive correlation.

Conclusions and relevance

This is the first major analysis of feline ultrasound-guided renal fine-needle aspiration cytology. This technique generates adequate samples for interpretation at rates comparable to other soft tissues and is most useful in the diagnosis of neoplasia. Some imaging characteristics are indicative of the likelihood of obtaining an adequate sample for cytologic interpretation.

Estimation of fetal lung development using quantitative analysis of ultrasonographic images in normal canine pregnancy

We investigated the quantitative analysis of sonographic images to predict fetal lung maturity of the canine foetus in normal pregnancy. Twelve bitches were recruited in the present study. Serial ultrasonographic exams were performed at three pre-determined time periods corresponding to the pseudoglandular (40-48 days of pregnancy), canalicular (49-56 days of pregnancy) and saccular phase (57-63 days of pregnancy) of lung development. Mean grey level (MGL) and the standard deviation of the histogram (SDH) of fetal lung and liver sonographic images were measured with dedicated software. The lung-to-liver ratio (LLR) for both parameters was also calculated. Measurements were taken on the two caudal-most foetuses and then averaged. SDH did not show any statistically significant difference between the three time periods in the lungs or in the liver. MGL measured in the lungs significantly increased in the first period and reached a plateau during the last two periods. Liver echogenicity was constant during the first two periods and significantly increased during the last week of gestation. The LLR of MGL significantly decreased during the last week of pregnancy. The LLR was a very good test to detect fetal lung maturity (area under the receiver operator curve (AUROC) = 0.875); using a cut-off value of LLR < 1.541, sensitivity was 83.33% and specificity was 83.33%, positive likelihood ratio = 5. LLR of MGL is an accurate test to estimate lung development in normal canine pregnancies.

Relationship of diagnostic accuracy of renal cortical echogenicity with renal histopathology in dogs and cats, a quantitative study

Background

Renal cortical echogenicity is routinely evaluated during ultrasonographic investigation of the kidneys. Both in dog and cat previous ex-vivo studies have revealed a poor correlation between renal echogenicity and corresponding lesions. The aim of this study was to establish the in-vivo relationship between renal cortical echogenicity and renal histopathology.

Results

Thirty-eight dogs and fifteen cats euthanized for critical medical conditions were included in the study. Ultrasonographic images of both kidneys were acquired ante mortem at standardized ultrasonographic settings. The echogenicity was quantified by means of Mean Gray Value (MGV) of the renal cortex measured with ImageJ. A complete histopathological examination of both kidneys was performed. Five kidneys were excluded because histopathology revealed neoplastic lesions. Only samples affected by tubular atrophy showed statistically different values in dog, and histopathology explained 13% of the total variance. MGV was not correlated neither to the degeneration nor to the inflammation scores. However, significant differences were identified between mildly and severely degenerated samples. Overall, the classification efficiency of MGV to detect renal lesions was poor with a sensitivity of 39% and a specificity of 86%.

In cats, samples affected by both tubular vacuolar degeneration and interstitial nephritis were statistically different and histopathology explained 44% of the total variance. A linear correlation was evident between degeneration and MGV, whereas no correlation with inflammation was found. Statistically significant differences were evident only between normal and severely degenerated samples with a sensitivity of 54.17% and a specificity of 83.3% and MGV resulted scarce to discriminate renal lesions in this species.

Conclusions

Renal cortical echogenicity shows low relevance in detecting chronic renal disease in dog whereas it results worth to identify severe renal damage in cat.

Texture analysis of B-mode ultrasound images to stage hepatic lipidosis in the dairy cow: A methodological study

Hepatic lipidosis is the most diffused hepatic disease in the lactating cow. A new methodology to estimate the degree of fatty infiltration of the liver in lactating cows by means of texture analysis of B-mode ultrasound images is proposed. B-mode ultrasonography of the liver was performed in 48 Holstein Friesian cows using standardized ultrasound parameters. Liver biopsies to determine the triacylglycerol content of the liver (TAGqa) were obtained from each animal. A large number of texture parameters were calculated on the ultrasound images by means of a free software. Based on the TAGqa content of the liver, 29 samples were classified as mild (TAGqa<50mg/g), 6 as moderate (50mg/g<TAGqa>100mg/g) and 13 as severe (TAG>100mg/g) in steatosis. Stepwise linear regression analysis was performed to predict the TAGqa content of the liver (TAGpred) from the texture parameters calculated on the ultrasound images. A five-variable model was used to predict the TAG content from the ultrasound images. The regression model explained 83.4% of the variance. An area under the curve (AUC) of 0.949 was calculated for <50mg/g vs >50mg/g of TAGqa; using an optimal cut-off value of 72mg/g TAGpred had a sensitivity of 86.2% and a specificity of 84.2%. An AUC of 0.978 for <100mg/g vs >100mg/g of TAGqa was calculated; using an optimal cut-off value of 89mg/g, TAGpred sensitivity was 92.3% and specificity was 88.6%. Texture analysis of B-mode ultrasound images may therefore be used to accurately predict the TAG content of the liver in lactating cows.

Sonographic Prediction of Pediatric Renal Scarring With Full Parameter Normalization

OBJECTIVES

To predict the chronic kidney disease (CKD) state for pediatric patients based on scaled renal cortical echogenicity.

METHODS

Sonograms from a cohort of 26 patients, half of whom had stage 4 or 5 CKD, whereas the other half had normal renal function, were analyzed. For each patient image, a region of interest (ROI) was drawn around the renal cortex for comparison with an ROI drawn around the hepatic parenchyma. The latter ROI was shifted spatially to normalize the signal attenuations and time-gain compensations of the two organs' ROIs. Then the average pixel intensity of the renal ROI was divided by the corresponding hepatic value, resulting in scaled renal cortical echogenicity.

RESULTS

The average scaled renal cortical echogenicity was higher for diseased than healthy kidneys by roughly a factor of 2 (2.01 [95% confidence interval, 1.62-2.40] versus 1.05 [95% confidence interval, 0.88-1.23] for normal kidneys). This difference was statistically significant (P < .001).

CONCLUSIONS

Our results show that the pediatric CKD state correlates with rigorously calculated scaled renal cortical echogenicity.

Perfusion- and diffusion-weighted magnetic resonance imaging of the liver of healthy dogs

OBJECTIVE To describe the perfusion and diffusion characteristics of the liver in healthy dogs as determined by morphological, perfusion-weighted, and diffusion-weighted MRI. ANIMALS 11 healthy adult Beagles. PROCEDURES Each dog was anesthetized and underwent morphological, perfusion-weighted, and diffusion-weighted MRI of the cranial aspect of the abdomen. On the MRI images, a region of interest (ROI) was established for each of 6 structures (aorta, caudal vena cava, portal vein, hepatic parenchyma, splenic parenchyma, and skeletal [epaxial] muscle). The signal intensity was determined, and a time-intensity curve was generated for each ROI. The apparent diffusion coefficient (ADC) was calculated for the hepatic and splenic parenchyma in diffusion-weighted MRI images, and the normalized ADC for the liver was calculated as the ratio of the ADC for the hepatic parenchyma to the ADC for the splenic parenchyma. Dogs also underwent abdominal ultrasonography, and ultrasound-guided fine-needle aspirate samples and biopsy specimens were obtained from the liver for cytologic and histologic examination. RESULTS Cytologic and histologic results suggested that the liver was clinically normal in all dogs. Perfusion-weighted MRI parameters varied among the 6 ROIs. The mean ± SD ADC of the hepatic parenchyma was 0.84 × 10(-3) mm(2)/s ± 0.17 × 10(-3) mm(2)/s, and the mean normalized ADC for the liver was 1.8 ± 0.4. CONCLUSIONS AND CLINICAL RELEVANCE Results provided preliminary baseline information about the diffusion and perfusion characteristics of the liver in healthy dogs. Additional studies on dogs of various breeds with and without hepatopathies are necessary to validate and refine these findings.

Correlation of renal histopathology with renal echogenicity in dogs and cats: an ex-vivo quantitative study

Background

Increased cortical or cortical and medullary echogenicity is one of the most common signs of chronic or acute kidney disease in dogs and cats. Subjective evaluation of the echogenicity is reported to be unreliable. Patient and technical-related factors affect in-vivo quantitative evaluation of the echogenicity of parenchymal organs. The aim of the present study is to investigate the relationship between histopathology and ex-vivo renal cortical echogenicity in dogs and cats devoid of any patient and technical-related biases.

Results

Kidney samples were collected from 68 dog and 32 cat cadavers donated by the owners to the Veterinary Teaching Hospital of the University of Padua and standardized ultrasonographic images of each sample were collected. The echogenicity of the renal cortex was quantitatively assessed by means of mean gray value (MGV), and then histopathological analysis was performed. Statistical analysis to evaluate the influence of histological lesions on MGV was performed. The differentiation efficiency of MGV to detect pathological changes in the kidneys was calculated for dogs and cats. Statistical analysis revealed that only glomerulosclerosis was an independent determinant of echogenicity in dogs whereas interstitial nephritis, interstitial necrosis and fibrosis were independent determinants of echogenicity in cats. The global influence of histological lesions on renal echogenicity was higher in cats (23%) than in dogs (12%).

Conclusions

Different histopathological lesions influence the echogenicity of the kidneys in dogs and cats. Moreover, MGV is a poor test for distinguishing between normal and pathological kidneys in the dog with a sensitivity of 58.3% and specificity of 59.8%. Instead, it seems to perform globally better in the cat, resulting in a fair test, with a sensitivity of 80.6% and a specificity of 56%.

Ultrasonographic quantification of hepatic-renal echogenicity difference in hepatic steatosis diagnosis

BACKGROUND AND AIM

Ultrasound (US) is recommended for hepatic steatosis screening. The purpose of this study was to determine the usefulness of US hepatic-renal echo-intensity (HR) difference in the quantitative assessment of hepatic steatosis.

METHODS

Consecutive patients undergoing liver biopsy were prospectively enrolled. Using US histogram technique, the mean gray level of hepatic parenchyma and right renal parenchyma at selected regions of interest were evaluated on the same day of biopsy. With steatosis assessed by histology as the reference, the diagnostic performances of HR difference in predicting the degree of steatosis was analyzed. The optimal cut-off level, diagnostic validity and post-test probability were assessed.

RESULTS

A total of 175 patients were enrolled (M/F, 103/72; mean age, 48.6 ± 11.7). There were 64 (36.5 %), 42 (24 %), 29 (16.6 %), 12 (6.9 %) and 28 (16 %) patients with steatosis of <5, 5-9, 10-19, 20-29 and ≥ 30 %, respectively. Multivariate analysis showed HR difference correlated with the severity of steatosis (R (2) = 0.425, p < 0.001) with positive correlation between HR difference and the severity of steatosis (r = 0.60, p < 0.001). The diagnostic performances were 0.927, 0.890, 0.816 and 0.760 for steatosis ≥ 30, ≥ 20, ≥ 10 and ≥ 5 %, respectively. The cut-off is 7 for diagnosing steatosis ≥ 30 %, with a negative predictive value of 97.6 %. The cut-off is 4 in predicting steatosis ≥ 5 %, with a positive predictive value of 79 %. The prevalence of steatosis influenced the post-test probability.

CONCLUSIONS

Quantitative assessment of HR difference with US histogram technique is useful in excluding moderate to severe hepatic steatosis.

Effect of anisotropy and spatial compound imaging on renal cortical echogenicity in dogs

The echogenicity of the renal cortex is an important parameter to consider in dogs that are suspected to have renal dysfunction. Focal increases in echogenicity have been attributed to neoplasia, infection, calcification, fibrosis, gas, and infarction. Anisotropic backscatter has been described as a source of focally increased renal cortical echogenicity in several species. The source of anisotropy appears to be the medullary rays, which are oriented perpendicular to the renal capsule. Spatial compound imaging (SCI) is an ultrasound setting that uses beam steering to acquire and average several overlapping scans of an object from different view angles, creating a compound image that is updated in real time. The impact of insonation angle and SCI on renal cortical echogenicity was evaluated ex vivo in eight kidneys from four dogs. Significant angle-dependent differences in cortical echogenicity were detected with both microconvex and linear transducers (P < 0.0001). Furthermore, the angle-dependent echogenicity differences persisted when SCI mode was used. Our finding that echogenicity was increased using a perpendicular insonation angle (90°) relative to the tubules, compared to a parallel insonation angle (0°) should assist in the interpretation of ultrasonographic images of the dog kidney.

Renal dimensions at ultrasonography in healthy Ragdoll cats with normal kidney morphology: correlation with age, gender and bodyweight

Fifty-six healthy Ragdoll cats underwent an ultrasonographical examination of the urinary tract to evaluate if gender, age, bodyweight and presence of a medullary rim sign had a significant influence on renal length and corticomedullary ratio (CM). Individual variation percentage was much more pronounced for renal length in comparison with CM ratio. Mean renal length measured 3.83 ± 0.45 cm (range 2.98–5.09 cm), mean cortical thickness 0.73 ± 0.15 cm (range 0.36–1.18 cm), mean medullary thickness 0.87 ± 0.19 cm (range 0.46–1.39 cm) and mean CM ratio 0.88 ± 0.29 (range 0.29–1.78). Renal length showed a significant positive correlation with bodyweight ( P <0.0001), age ( P = 0.0073) and male gender ( P <0.0001). Therefore, these parameters have to be kept in mind when evaluating renal length on ultrasound. The CM ratio was solely influenced by the presence of a medullary rim sign ( P <0.0001). Further research, however, is needed to investigate the usefulness of the CM ratio for the detection of kidney disease by ultrasonography.

Ultrasonography of the feline kidney: Technique, anatomy and changes associated with disease

PRACTICAL RELEVANCE

Ultrasonography is an important tool for the detection of kidney disorders, which are among the most common health problems suffered by cats. It is more accurate than radiography for this purpose and is considered to be the reference modality for imaging the feline kidney, providing excellent visualisation of renal size, shape and internal architecture. Compared with more advanced imaging modalities, such as computed tomography or magnetic resonance imaging, ultrasonography is more accessible, less expensive, does not require general anaesthesia and allows real-time procedures to be performed.

CLINICAL CHALLENGES

On ultrasound examination, focal or multifocal disorders may be readily identified, but diffuse changes are more challenging. B-mode ultrasonography is of limited use for differentiating between benign and malignant focal lesions. However, based on the presence and pattern of vascularity as an indicator of malignancy, contrast-enhanced ultrasonography allows distinction between benign and malignant focal renal lesions.

AUDIENCE

This review provides a framework for the ultrasonographic approach to feline renal and perirenal disorders for the general practitioner.

EVIDENCE BASE

Drawing on current literature relating to ultrasonographic examination of feline kidneys, the aim is to summarise ultrasonographic technique, anatomy and changes associated with renal and perirenal diseases.

Ultrasound imaging in an experimental model of fatty liver disease and cirrhosis in rats

BACKGROUND

Domestic dogs and cats are very well known to develop chronic hepatic diseases, including hepatic lipidosis and cirrhosis. Ultrasonographic examination is extensively used to detect them. However, there are still few reports on the use of the ultrasound B-mode scan in correlation with histological findings to evaluate diffuse hepatic changes in rodents, which represent the most important animal group used in experimental models of liver diseases. The purpose of this study was to determine the reliability of ultrasound findings in the assessment of fatty liver disease and cirrhosis when compared to histological results in Wistar rats by following up a murine model of chronic hepatic disease.

RESULTS

Forty Wistar rats (30 treated, 10 controls) were included. Liver injury was induced by dual exposure to CCl4 and ethanol for 4, 8 and 15 weeks. Liver echogenicity, its correlation to the right renal cortex echogenicity, measurement of portal vein diameter (PVD) and the presence of ascites were evaluated and compared to histological findings of hepatic steatosis and cirrhosis. Liver echogenicity correlated to hepatic steatosis when it was greater or equal to the right renal cortex echogenicity, with a sensitivity of 90%, specificity of 100%, positive and negative predictive values of 100% and 76.9% respectively, and accuracy of 92.5%. Findings of heterogeneous liver echogenicity and irregular surface correlated to liver cirrhosis with a sensitivity of 70.6%, specificity of 100%, positive and negative predictive values of 100% and 82.1% respectively, and accuracy of 87.5%. PVD was significantly increased in both steatotic and cirrhotic rats; however, the later had greater diameters. PVD cut-off point separating steatosis from cirrhosis was 2.1 mm (sensitivity of 100% and specificity of 90.5%). One third of cirrhotic rats presented with ascites.

CONCLUSION

The use of ultrasound imaging in the follow-up of murine diffuse liver disease models is feasible and efficient, especially when the studied parameters are used in combination. The potential implication of this study is to provide a non-invasive method that allows follow-up studies of fatty liver disease and cirrhosis of individual rats for pre-clinical drug or cell based therapies.

Quantitative assessment of renal cortical echogenicity in clinically normal cats

In this study, we assessed the renal cortical echogenicity of clinically normal adult cats by histogram analysis to obtain basic ultrasonographic data. Ultrasound images were taken under the following sets of conditions: (1) high contrast and low gain setting using a convex probe, (2) low contrast and high gain setting using a convex probe, (3) high contrast and low gain setting using a linear probe and (4) low contrast and high gain setting using a linear probe. Echogenicity of the region of interest (ROI) in the right and left renal cortices, liver and spleen was determined by histogram analysis; kidney/spleen (Kid/Sp) and kidney/liver (Kid/Liv) echogenicity ratios were calculated. Kid/Sp and Kid/Liv values varied among different ROI sites in the kidney when obtained using the convex probe, but were constant when obtained using the linear probe. Kid/Sp measured in the middle sites of the kidney showed similar values for the different settings; however, Kid/Liv differed between probes. The present findings suggest that determination of Kid/Sp using a linear probe is a feasible method for quantitative evaluation of renal cortical echogenicity in cats.

Statistical relevance of ultrasonographic criteria in the assessment of diffuse liver disease in dogs and cats

OBJECTIVE

To determine whether objectively applied ultrasonographic interpretive criteria are statistically useful in differentiating among 7 defined categories of diffuse liver disease in dogs and cats.

SAMPLE POPULATION

Ultrasonographic images of 229 dogs and 104 cats.

PROCEDURES

Liver parenchymal or related sonographic criteria established by the authors were retrospectively and independently applied by 3 radiologists who were not aware of patient status or patient laboratory data. Seven histologic or cytologic categories of diffuse (infiltrative but not nodular) liver diseases were jointly established by the authors and included normal liver; inflammation; round-cell neoplasia; non-round-cell infiltrative, prenodular (early) metastatic neoplasia; lipidosis; vacuolar hepatopathy; and other. Liver parenchymal sonographic criteria included parenchymal sound attenuation with increasing depth, comparative organ echogenicity (liver, spleen, and kidneys), diffuse or patchy hyperechoic or hypoechoic echotexture, uniform or coarse echotexture, portal venous clarity, and liver lobe geometry. Related extrahepatic criteria included gallbladder wall thickness, bile duct diameter, amount and character of gallbladder precipitate, nondependent shadowing in the gallbladder, hepatic vein diameter versus caudal vena cava diameter, peritoneal fluid, spleen echotexture (normal vs abnormal [characterized]), and kidney echotexture. Ultrasonographic criteria were statistically compared to the 7 categories of diffuse liver disease in search of clinically exploitable relationships.

RESULTS

Statistical evaluation of the applied ultrasonographic criteria did not yield clinically acceptable accuracy for discrimination among the 7 categories of diffuse liver diseases (including normal liver) in either species.

CONCLUSIONS AND CLINICAL RELEVANCE

Criterion-based ultrasonographic appearance was insufficient to discriminate among canine and feline diffuse infiltrative liver diseases.

Development, advances and applications of diagnostic ultrasound in animals

Ultrasound has many industrial applications but it was first introduced as a medical diagnostic aid in the 1940s with its first veterinary application, the detection of ovine pregnancy, being reported in 1966. Since then, improvements in equipment quality combined with an increased awareness of the benefits of ultrasound as an imaging technique have led to its widespread use in the veterinary field. Recent advances in computer technology have significantly influenced equipment design and the miniaturization of transducers allows intra-operative and intra-vascular applications. Software advances have improved the ability to manipulate and process data, leading to an increased amount of information being obtained from each examination and the advent of 'remote diagnosis'. Ultrasound guided interventional techniques can now be used for diagnostic or therapeutic purposes. Many of these developments have been introduced by equipment manufacturers but have found specific applications in the veterinary field. Ultrasound is currently employed in a very diverse range of situations, not just as a diagnostic tool in the routine clinical workup of a range of species, but also for disease screening, conservation projects, commercial services, herd management and clinical research.

Increased Echogenicity as a Predictor of Poor Renal Function in Children With Grade 3 to 4 Hydronephrosis

PURPOSE

Prenatally diagnosed hydronephrosis is a common finding that often requires further radiological evaluation to determine whether it is associated with compromised renal function. We hypothesize that findings on postnatal renal sonography may help determine which patients require more extensive evaluation of renal function in the assessment for prenatal hydronephrosis. We show that increased renal parenchymal echogenicity on postnatal US is a strong predictor of compromised renal function.

MATERIALS AND METHODS

A total of 97 patients diagnosed with prenatal hydronephrosis presented to our institution for furosemide (99m)technetium MAG3 renogram evaluation of renal function between January 2000 and December 2001. All patients had SFU grade 3 to 4 hydronephrosis noted on postnatal US before age 6 months. For these 97 patients (178 renal units) we correlated the degree of renal parenchymal echogenicity and parenchymal thinning on the first postnatal sonogram with the differential renal function as determined by furosemide MAG3 renography.

RESULTS

Among 97 patients diagnosed with prenatal hydronephrosis 10 of 20 renal units (50%) with markedly increased echogenicity had severely decreased relative renal function of less than 10%, while 136 of 151 (90%) with normal echogenicity exhibited normal relative renal function of 40% or greater. Increased echogenicity on US yielded a sensitivity of 100% and specificity of 99% for predicting relative renal function of 20% or greater. In predicting relative renal function of 40% or less sensitivity and specificity were 48% and 100%, respectively.

CONCLUSIONS

Increased renal parenchymal echogenicity found on the first postnatal ultrasound can be used as a predictor of impaired relative renal function as measured on furosemide MAG3 renogram.