Urinary stones are a common disease affecting one in 11 people . Their clinical presentation varies from being silent to severe loin pain owing to urinary obstruction. Currently, ESWL is the treatment of choice for most renal calculi ⩽30 mm, with success rates of 60-99%. Although many treatment options exist, ESWL has the advantages of simplicity and non-invasiveness. In contrast, failure of a first ESWL attempt requires a follow-up ESWL procedure, or an alternative procedure, both of which increase medical costs.

Advancements in imaging have significantly contributed to this process. In the mid- 1990s, computed tomography (CT) began to replace intravenous urography (IVU), abdominal films (KUB), and ultrasound (US) in stone diagnosis. Studies demonstrated that CT had superior sensitivity and specificity for stone diagnosis compared to the aforementioned modalities. Now non-contrast multidetector CT (NC-MDCT) is the gold standard for the detection of urinary system calculi. CT is also clinically useful as it can show alternate renal and non-renal pathology if present.

Many factors have been reported to predict ESWL outcome, such as skin-to-stone distance (SSD), stone size, stone location, multiplicity, the energy used, and Hounsfield Unit (HU) values measured by non-contrast computed tomography (NCCT).

Excellent fragmentation results are produced using ESWL. However, the retention of post-ESWL fragments in the kidney continues to be a significant medical issue. Only 32% of calcium stone patients in research were found to remain stone-free for 12 months following ESWL, according to the results. As a result, it appears that fragment growth and persistence are frequent after ESWL [10].

The first ESWL residual that is accessible must undergo a thorough stone analysis to properly carry out the subsequent treatments to prevent relapse or recurrent stone because stone-free rates after ESWL are directly connected to stone placement, size, number, and composition

Inclusion Criteria:

• patients older than 18 years.
• stone size up to 25 mm for renal pelvic stones and up to 15 mm for upper ureteric stones.
• SSD < 11 cm.

Exclusion Criteria:

• any patient with contraindications to ESWL as
• uncontrolled urinary infection.
• clotting alterations.
• aortic or renal artery aneurysm.
• pregnancy.
• serious skeletal malformations.
• serious obesity and or contraindications to CT as pregnancy.

• Firstly All studies were performed by using a CT device.
• the mean Hounsfield unit was calculated. The skin-to-stone distance (SSD) was calculated by measuring three distances from the stone to the skin at 0, 45, and 90°;
• after the first session of ESWL by one to three weeks Low dose NCCT(MA=175)will be done to determine the measurements of the fragments or the stone if not fragmented including their density and size will be taken, For the density, if decreased or not changed continuation versus stop will be evaluated, while for the size the fragmentation will be assessed as 1- complete fragmentation is the fragment size <4 mm, 2- partial fragmentation if size = 4-5 mm and 3- incomplete fragmentation if the size of fragment more than or equal 6 mm.