International Journal of Nephrology Ultrasound imaging of the kidneys is very useful in the diagnosis of obstructive uropathy. In fact, a negative kidney US exam for hydronephrosis rules out obstruction as the cause of AKI. When dilatation of calyces and proximal ureter is found, the diagnosis of urinary tract obstruction can be made. However, dilatation of renal calyces alone does not always indicate urinary tract obstruction. In fact, caliceal dilatation can be found during pregnancy and also in cases with diabetes insipidus [26, 27]. Dilatation of the distal ureter may provide clues for presence of obstruction at the level of bladder or urethra. 3. Role of Ultrasound in Management of CRS Patients In patients suspicious of CRS, echocardiogram provides valuable information on cardiac structure and function and should be considered as one of the initial diagnostic studies. Around 27–40% of patients with acute decompensated heart failure (HF) develop acute kidney injury (AKI) [28]. At the same time, 45 to 63% of patients with chronic HF have CKD [29, 30]. Acute decompensated heart failure can occur in the setting of either systolic or diastolic dysfunction. Echocardiogram is the most useful diagnostic test in evaluating the cause of acute HF. In addition to providing information on systolic and diastolic function of the heart, echocardiogram is very useful in assessing regional wall motion abnormalities, condition and function of heart valves, and hemodynamics. Echocardiogram can also be used to rule out pericardial disease. Systolic HF is deﬁned as combination of symptoms of HF and LVEF less than 50%. Heart Failure with normal LVEF, also referred to as diastolic dysfunction, was not recognized as an entity by the cardiology community until about two decades ago. Patients with HF and normal LVEF usually have normal or reduced LV size, but enlarged left atria [31]. Although it is thought that LVH is the cause of HF with normal LVEF, the criteria for its diagnosis are only met in less than 50% of cases with HF and normal EF. Instead, these individuals have increased LV mass-to-volume ratio [32]. Doppler echocardiogram can provide valuable information on LV relaxation, ﬁlling pressures, and stiﬀness. However, this information needs to be interpreted carefully with special attention to clinical presentation (acute versus chronic, presence of symptoms, blood pressure readings, etc.). The 2007 consensus statement of the Heart Failure and Echocardiography Associations of the European Society of Cardiology suggested 3 essential criteria for the diagnosis of diastolic heart failure or heart failure with normal ejection fraction. They are presence of signs and symptoms of HF, normal or mildly abnormal LV size and systolic function (LVEF > 50% and an LV end-diastolic volume < 97 mL/m2), and evidence of LV diastolic dysfunction via invasive or noninvasive methods. Renal ultrasonography is valuable in diﬀerentiating between acute and chronic kidney disease and ruling out obstruction as a cause of worsening renal function. In cases suspicious of type 1 CRS, a normal renal ultrasound 3 examination is expected. This is due to the acute nature of condition and the fact that reduced GFR is resulting from renal hypoperfusion. An exception would be cases in which acute HF results in acute worsening of GFR from an already low baseline level, or acute on chronic KD. In these cases, US features of CKD do not rule out the possibility of CRS type 1. Availability of previous kidney ultrasound images for comparison would be of great value in these cases. A few small single center studies suggest a role for Doppler ultrasound in the diﬀerential diagnosis of AKI. In one study, a normal (<0.71) resistive index [(peak systolic velocity − peak diastolic velocity)/peak diastolic velocity)] measured at the level of segmental renal arteries was seen in all individuals with a low fractional excretion of sodium (FENa), while individuals with high FENa had high resistive indices [33]. Among those with acute tubular necrosis and high FENa at baseline, there was a signiﬁcant reduction in the RI after recovery from AKI episode [33]. 4. Other Imaging Studies 4.1. Imaging of the Heart. Although echocardiogram is considered the imaging modality of choice in the workup of HF patients, in some cases more information on the structure and function of the heart might be necessary. In order to measure LVEF and volumes by echocardiography, a clear deﬁnition of endocardium is needed. This information is lacking in as many as 31% of cases [34]. Other imaging techniques might be needed to obtain more detailed infor- mation in these cases. The most commonly used imaging in nuclear car- diology is single-photon emission computed tomography (SPECT) imaging of myocardial perfusion. After injection of the radiotracer, the isotope is extracted from the blood by viable myocytes and retained within the myocyte for some period of time. The photons are emitted from the myocardium which is in proportion to the magnitude of tracer uptake, and thus relates to perfusion. A gamma camera captures the photons and converts it into digital data which represents the magnitude of uptake and location of emission. Myocardial perfusion scanning using intravenous injection of technetium-99m- (99mTc-) labeled agents such as sestamibi 99mTc-labeled RBCs can be used for assessment of LVEF and regional wall motion abnormalities. Radionuclide imaging can be used to study the structure and function of the heart at rest and after exercise. LVEF, end-systolic, and end-diastolic volumes can be accurately measured by processing three dimensional images on gated SPECT using 99mTc agents [9]. Radionuclide ventriculography can be used to assess the left ventricular function. It can be performed either as ﬁrst pass or equilibrium-gated techniques. Both techniques provide reliable means to asses the left and right ven- tricular function. The equilibrium technique is referred to as multiple-gated acquisition (MUGA) scanning. The RVG technique has advantages over echocardiography as there are no assumptions made about the ventricular geometry. Thus radionuclide imaging can provide accurate data about ventricular function [35].