2 tissue penetration, high frequency transducers are used for imaging of superﬁcial structures. Imaging of the heart and the kidneys requires frequencies in the range of 2–5 MHz (lower frequencies) to guarantee deeper penetration into the body. Imaging using ultrasound is limited in presence of gas and boney structures. High degree of reﬂection of US waves at the junction of soft tissue and gas or bone results in loss of signal from tissues beyond that point. 2.1. Echocardiography. Echocardiography is considered the preferred diagnostic method in cases suspicious of having heart failure [9]. It is a safe, noninvasive, and reproducible test applicable at bedside that provides valuable information on the anatomy and function of the heart. Using echocar- diography, one can assess the structure of the myocardium and pericardium, global and regional LV function, and wall motion at rest and during pharmacologic stress. Two- dimensional (2D), gray-scale, or B (for brightness) mode echocardiography provides real-time images of heart struc- tures and their motion. By imaging the heart in diﬀerent planes, information on the dimensions, surface area, and volume of diﬀerent chambers of the heart and valves can be obtained. M (for motion) mode echocardiography image is the graphic representation of the movement of cardiac structures based on the 2D image. Doppler echocardiogra- phy and color ﬂow imaging provides information on the blood ﬂow velocities and the pattern of blood ﬂow within the heart. Pulsed and continuous wave Doppler US provide information on the velocity of blood ﬂow in a speciﬁc location or the whole area within the path of ultrasound, respectively. Color ﬂow Doppler provides information on velocity, turbulence, and direction of blood ﬂow in the form of a colorful image superimposed on a 2D image. Echocardiography provides useful information on left ventricular (LV) function. These include LV ejection fraction (LVEF), stroke volume, cardiac index, fractional shortening and regional wall motion analysis, among others. LVEF is the fraction of the left ventricular volume at the end of diastole that is ejected at the end of each contraction. Although there are objective ways to measure LVEF by plugging in accurate measurements of LV dimensions or volumes into a formula, in most cases, LVEF is a visual estimation of LV function and its accuracy depends on the experience of the interpreter. In one study of individuals with heart failure and reduced LVEF 6 months after a myocardial infarction [10], the overall accuracy of echocardiography in correctly assessing radionuclide ventriculography LVEF was 86%. In only one of 86 patients studied, there was a clinically signiﬁcant diﬀerence between LVEFs estimated by the two methods (low LVEF by echocardiogram and normal LVEF by radionuclide technique) [10]. In another study, LVEF estimated by either echocardiography or electrocardiogram-gated single photon emission computed tomography (SPECT) were lower than those obtained by angiography. But they both did similarly well in accurately assessing LVEF of less than 40% or 35% in comparison to angiography [11]. Despite its limitations [12], determination of LVEF by 2-dimensional echocardiography is well accepted as the preferred measure of global LV function. International Journal of Nephrology Certain echocardiographic parameters such as LV end- diastolic volume index, mitral deceleration time, and severity of mitral valve regurgitation are strong predictors of out- comes in individuals with advanced heart failure and reduced LVEF [13]. As many as 50% of all cases with clinical symptoms of heart failure have preserved LV function. Therefore, assessment of diastolic function in these cases is criti- cal. Echocardiography is the noninvasive way of assessing diastolic function. Since almost 80% of LV ﬁlling during diastole (relaxation of the LV) occurs passively, abnormal relaxation of myocardium would result in impaired LV ﬁlling and diastolic dysfunction. M-mode, 2D, and Doppler echocardiogram are all useful in making the diagnosis of diastolic dysfunction and predicting outcomes [14]. Diastolic dysfunction can be graded based on the ﬁlling pressures and mitral inﬂow patterns obtained by echocardiography. Spectral tissue Doppler-derived index E/E appears to be a valuable tool in assessing left atrial pressure [15]. E and E represent peak early diastolic mitral ﬂow and mitral annulus velocities, respectively. This index has shown a linear relationship with LV diastolic pressure irrespective of LVEF, heart rhythm, and rate [15]. The diagnostic accuracy of E/E is similar to that of B-type natriuretic peptide (BNP) in diagnosis of patients presenting with symptoms of heart failure with a wide range of LVEF [16]. Septal E/E at a cut-oﬀ value of 13 in patients presenting with acute dyspnea and preserved systolic function has a sensitivity of 76%–82% and speciﬁcity of 88%–91% for diagnosis of heart failure [17, 18]. 2.2. Renal Ultrasonography. Kidney size and the echogenecity of the renal parenchyma provide useful information in the workup of kidney diseases. Normal kidney measures 9–13 cm in long axis. Length of the kidney correlates with height of the person while kidney volume correlates with weight, body surface area, and height [19]. Small kidney size is consistent with chronic kidney disease (CKD). However, not all CKD cases are associated with small kidneys. Normal or enlarged kidneys are seen in cases with HIV-associated nephropa- thy (HIVAN) [20], diabetic nephropathy, and monoclonal gammapathies. Within the renal cortex the back scatter of the US waves occurs mainly from the glomeruli and blood. In general, normal renal cortex generates an US image that is less echogenic or darker than the adjacent liver tissue at the same depth. Increased echogenecity of renal cortex, that is, same or brighter than the liver, indicates renal disease. This ﬁnding on the gray-scale US has a speciﬁcity of 96% and positive predictive value of 67% for diagnosis of kidney disease [21]. Since glomeruli occupy only 8% of the cortical volume, isolated glomerular disease will not produce increased echogenecity [22]. Increased cortical echogenecity is usually indicative of CKD. However, echogenic kidneys can also be seen in cases with acute kidney injury (AKI). As an example, large and swollen kidneys with increased echogenecity are reported in cases with acute tubular necrosis (ATN) or lupus nephritis [23–25].