The CT has generally been used for localization of the kidney prior to kidney biopsy in situations in which localization is unsatisfactory by ultrasound, e.g. very large patient girth, and often when optimal localization is particularly critical, e.g., in a patient with a solitary kidney.

    More recently elective use of the CT has been employed by increasing numbers of nephrologists, and an increasing proportion of kidney biopsies are being performed by radiologists with extensive interventionalist skills.

    It is my impression that either ultrasound or CT is equally suitable as a technique for satisfactorily imaging the kidney for percutaneous biopsy, and the decision is largely a matter of personal preference by the operating physician, in the absence of some specific factor making one or the other of the techniques more suitable.

    I have no information on the comparative costs of these two techniques.

    Following positioning and prepping of the patient, a preliminary localization of the kidneys is obtained, and a point on the skin overlying the lower pole of the kidney is marked for reference

A point over the lower pole of the selected kidney is marked, and the distance from the point to the capsule is determined.	The selected needle is inserted partway to the kidney, and an image is taken to guide positioning of the needle.
An additional measurement is made from the tip of the needle to the capsule of the kidney, and the needle is repositioned.	When the tip of the biopsy needle has been positioned at the capsule of the kidney, the biopsy may be performed.

CT-directed kidney biopsies are now usually performed using one the several automatic or semi-automatic disposable needles, but the Silverman reusable stainless steel needle may also be employed, as illustrated in the above photographs.

An occasional disadvantage of using CT to direct the kidney biopsy may occur when multiple biopsy passes are required to obtain an adequate sample.  If the operating physician is required to rely heavily on the CT image to position the needle, multiple series of sequential needle repositioning and repeat imaging steps may be required, making the procedure time-consuming and more difficult for all involved.  

An at least somewhat novel approach, which I have observed to be remarkably effective, involves the use of two biopsy needles.  In this procedure, the Silverman needle is introduced initially as a guide, positioned with its tip just outside the capsule of the kidney, followed by the performance of the actual biopsy with an automatic "two-button" needle, inserted through the "indwelling" Silverman needle down to the capsule of the kidney, where the definitive biopsy needle is then fired.

Steps in this two-needle biopsy technique are illustrated below.

The outer cylinder of the Silverman needle (left) with the trochar removed (right) is shown.  The inner cutting needle (not shown)  will not be used.	An two-button automatic needle will be used for the definitive biopsies.
With the patient properly positioned and draped, a point overlying the selected kidney is identified, and the length from the selected point to the kidney below is determined.	Using a ruler, the estimated kidney depth is marked on the biopsy needle, using either a marking pen, or other means.

In this case the estimated required needle length has been marked with an adhesive bandage.	The marked Silverman needle has been introduced approximately to the capsule of the kidney.

After the positioning of the Silverman needle is checked by CT, with repositioning as required, the Silverman needle is left in situ, as a needle guide, permitting several biopsies to obtained through the optimally localized Silverman needle.

The cocked needle is inserted through the Silverman guide to the surface of the kidney and the biopsy is obtained.	Since the needle guide remains in place, multiple biopsies may be taken until sufficient material is obtained.

Not illustrated above, the total length of the needle guide may be marked on the shaft of the automatic needle, simplifying positioning the biopsy needle at the tip of the guide needle.

The essence of this procedure is that the larger guide needle remains positioned just outside the capsule of the kidney, permitting multiple biopsies to be taken through this carefully pre-positioned guide needle.

It is my impression that this double needle technique, described above, generally simplifies the process of CT-guided kidney biopsy, allowing the biopsy to be performed in less time, with more definitive localization of the needle, and with the distinct advantage that multiple biopsies can be obtained, as required, with a smaller and possibly safer needle.