The Virginia Supreme Court ruled Friday that courts cannot rely on a machine that measures sexual arousal of accused sex offenders without evidence to back up the machine's accuracy.

The court ruled in a Tazewell County case in which a teenager was sentenced to two life terms for orally sodomizing a 9-year-old boy.

Circuit Court Judge Henry A. Vanover imposed the sentence based in part on the results of a penile plethysmograph, a controversial device akin to a polygraph. The machine measures blood flow to the penis.

Matthew E. Billips was convicted of two counts of forcible sodomy and one count of soliciting a child to perform sodomy. Billips was living at a relative's house in May 2003 when he exchanged oral sex with the boy and tried to persuade another young boy to commit the same act, according to the trial evidence.

Billips, now 21, maintains his innocence and claims that his relatives set him up over a drug deal gone sour.

A jury found him guilty and sentenced him to 25 years in prison.

Vanover, however, citing Billips' criminal record, the nature of the offense and the harm done to the boys, imposed two life terms plus five years. The judge said he could not

• "imagine any more a heinous offense than what you have committed."

Before imposing sentence, Vanover ordered Billips to undergo a psychosexual evaluation, which included a plethysmograph. Billips became aroused when shown pictures of boys and girls in sexual situations. The report placed him in the highest risk category for re-offending.

Billips' attorney objected to the use of the test results, to no avail. The Virginia Court of Appeals also upheld the circuit judge. The Virginia Supreme Court has now sent the case back to Tazewell County for a new sentencing.

If the circuit judge plans to use the test results, he must find some scientific basis for its accuracy, the court ruled.

Scientists are divided on the reliability of the plethysmograph. Some have found it accurate in determining recidivism among sex offenders. Others have found it unreliable, and some states prohibit its use entirely.

The 4th U.S. Circuit Court of Appeals ruled in a 2002 case that the plethysmograph lacks "scientific validity" and is prone to false positives.

L. Steven Emmert, a Virginia Beach lawyer who tracks Virginia's appellate rulings, wonders what Vanover - having already seen the test result - will do when the case returns.

• "That's the real question," he said.

A spokesman for the attorney general's office, which argued the case, declined to comment.

Billips' appellate attorney, James R. Henderson IV, a Norfolk native and Old Dominion University graduate, said he welcomes the ruling and hopes that Billips' new sentence will not be as harsh.

• "It can't get any worse," he said.