6. STOCKHOLDERS' EQUITY (Details Narrative) - USD ($)	3 Months Ended
	Jul. 31, 2017	Jul. 31, 2016
Commissions and other issuance costs	$ 111,000	$ 55,000
June 2017 [Member]
Liquidation preference	$ 25.00
Stock Incentive Plans [Member]
Shares reserved for future issuance	5,612,106
ESPP [Member]
Shares reserved for future issuance	1,359,736
Warrants [Member]
Shares reserved for future issuance	39,040
Common Stock [Member]
Proceeds from issuance of stock	$ 4,304,000
Common Stock [Member] | August 2015 AMI Sales Agreement [Member]
Remaining Aggregate Gross Proceeds Available Under Agreement	0
Proceeds from issuance of stock	$ 4,304,000
Shares issued, new	1,051,258
Commissions and other issuance costs	$ 111,000
Series E Preferred Stock [Member]
Shares reserved for future issuance	6,826,435
Series E Preferred Stock [Member] | June 2017 [Member]
Declaration Date	Jun. 06, 2017
Dividend per share	$ 0.65625
Annualized percentage rate	10.50%
Accrual period	April 1, 2017 through June 30, 2017
Record date	Jun. 19, 2017
Payment date	Jul. 03, 2017
Dividend paid	$ 1,081,000